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  • 1. Arleth, L.
    et al.
    Bergström, Lars Magnus
    KTH, Tidigare Institutioner                               , Kemi.
    Pedersen, J. S.
    Small-angle neutron scattering study of the growth behavior, flexibility, and intermicellar interactions of wormlike SDS micelles in NaBr aqueous solutions2002Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 18, nr 14, s. 5343-5353Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    SDS wormlike micelles in water with NaBr are studied using small-angle neutron scattering. SDS concentrations ranging from 0.08 to 8.6 % vol in NaBr aqueous solutions at salinities from 0.6 to 1.0 M are covered. The scattering data are analyzed using a novel approach based on polymer theory and the results of Monte Carlo simulations. The method makes it possible to give a full interpretation of the scattering data, even for the entangled micellar solutions occurring at high concentrations and high salinities. Analysis of the scattering data at zero scattering angle demonstrates that the length of the micelles increases according to a power law as a function of concentration in the studied interval. The analysis furthermore shows that the length of the micelles increases exponentially with increasing salinity. The scattering data in the full range of scattering angles are analyzed using a model for polydisperse wormlike micelles where excluded volume effects are taken into account via an expression based on the polymer reference interaction site model (PRISM). This part of the analysis show that the micelles become more flexible as the salinity increases, which is due to an increased screening of the ionic micelles.

  • 2.
    Bastardo Zambrano, Luis Alejandro
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    Garamus, V. M.
    GKSS Research Centre, Geesthacht.
    Bergström, Lars Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    Claesson, Per M.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    The structures of complexes between polyethylene imine and sodium dodecyl sulfate in D2O: a scattering study2005Inngår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 109, nr 1, s. 167-174Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The association between a highly branched polyelectrolyte with ionizable groups, polyethylene imine (PEI), and an anionic surfactant, sodium dodecyl sulfate (SDS), has been investigated at two pH values, using small-angle neutron and light scattering. The scattering data allow us to obtain a detailed picture of the association structures formed. Small-angle neutron scattering (SANS) measurements in solutions containing highly charged PEI at low pH and low SDS concentrations indicate the presence of disklike aggregates. The aggregates change to a more complex three-dimensional structure with increasing surfactant concentration. One pronounced feature in the scattering curves is the presence of a Bragg-like peak at high q-values observed at a surfactant concentration of 4.2 mM and above. This scattering feature is attributed to the formation of a common well-ordered PEI/SDS structure, in analogue to what has been reported for other polyelectrolyte-surfactant systems. Precipitation occurred at the charge neutralization point, and X-ray diffraction measurements on the precipitate confirmed the existence of an ordered structure within the PEI/SDS aggregates, which was identified as a lamellar internal organization. Polyethylene imine has a low charge density in alkaline solutions. At pH 10.1 and under conditions where the surfactant was contrast matched, the SANS scattering curves showed only small changes with increasing surfactant concentration. This suggests that the polymer acts as a template onto which the surfactant molecules aggregate. Data from both static light scattering and SANS recorded under conditions where SDS and to a lower degree PEI contribute to the scattering were found to be consistent with a structure of stacked elliptic bilayers. These structures increased in size and became more compact as the surfactant concentration was increased up to the charge neutralization point.

  • 3.
    Bergström, L. Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Explaining the growth behavior of surfactant micelles2015Inngår i: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 440, s. 109-118Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The growth behavior of surfactant micelles has been investigated from a theoretical point of view. It is demonstrated that predictions deduced from the spherocylindrical micelle model, which considers micelles that are only able to grow in the length direction, are inconsistent with experimental measurements. Accordingly, the rise in aggregation numbers above a certain concentration, roughly corresponding to the second critical micelle concentration, appears to be much stronger than predicted by the spherocylindrical micelle model. On the other hand, predictions deduced from the general micelle model, which considers micelles that are able to grow with respect to both width and length, show excellent agreement with experimental observations. The latter theory is based on bending elasticity and it is demonstrated that the associated three parameters spontaneous curvature, bending rigidity and saddle-splay constant may all be determined for a micellar system from experimental measurements of the aggregation number as a function of surfactant concentration. The three parameters turn out to influence the appearance of a micellar growth curve rather differently. In accordance, the location of the second cmc is mainly determined by the saddle-splay constant and the bending rigidity. The shape of the growth curve, when going from the region of weakly growing micelles at low surfactant concentrations to strongly growing micelles above the second cmc, is mainly influenced by the bending rigidity.

  • 4.
    Bergström, L. Magnus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Aratono, Makoto
    Synergistic effects in mixtures of two identically charged ionic surfactants with different critical micelle concentrations2011Inngår i: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 7, nr 19, s. 8870-8879Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Expressions for the critical micelle concentration (cmc) and activity coefficients as functions of surfactant composition in mixtures of two identically charged monovalent ionic surfactants are derived from the nonlinear Poisson-Boltzmann (PB) theory. For the special case of no added salt, the simple expression cmc(alpha) = xcmc(1)(alpha) + (1 - x)cmc(2)(alpha) is deduced, where the exponential parameter alpha > 1 depends on the number of ionic species in a surfactant molecule as well as the curvature of the self-assembled interface. Theoretical predictions are compared with cmc values obtained with some different experimental techniques for mixtures of the two cationic surfactants didodecyldimethylammonium bromide (DDAB) and dodecyltrimethylammonium bromide (DTAB) in water and in the absence of added salt. It is demonstrated that the PB theory generates significantly better agreement with experimental data than predicted by ideal behaviour or the regular mixture theory. We find that maximum synergistic effects occur at a DDAB mole fraction in solution y = 0.005. According to the PB theory, this very low value of y corresponds to a mole fraction of DDAB in the self-assembled interfacial aggregates equal to x = 0.995. Moreover, our calculations of the surfactant composition in the self-assembled interfacial aggregates above cmc demonstrate that the transition from small micelles to large bilayer aggregates is found to consistently occur at a mole fraction of DDAB equal to about x = 0.41-0.42, irrespective of the surfactant molar ratio in solution. Experimental observations strongly support the fact that concentrations of free surfactant, as well as the surfactant composition in the self-assembled interfacial aggregates, may be accurately calculated from the non-linear Poison-Boltzmann theory. On the other hand, a micelle-to-bilayer transition induced by changes in surfactant mole fraction in the self-assembled interfacial aggregates is consistent with neither ideal surfactant behaviour nor synergistic behaviour according to the regular mixture theory.

  • 5.
    Bergström, L. Magnus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Garamus, Vasil M.
    Geometrical Shape of Micelles Formed by Cationic Dimeric Surfactants Determined with Small-Angle Neutron Scattering2012Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, nr 25, s. 9311-9321Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of spacer group on the geometrical shape of micelles formed by quaternary-bis dimeric (Gemini) surfactants C12H25N(CH3)(2)(CH2)(5)N(CH3)(2)C12H25 (12-s-12) has been investigated with small-angle neutron scattering (SANS). Dimeric surfactants with a short spacer unit (12-3-12 and 124-12) are observed to form elongated general ellipsoidal micelles with half axes a < b < c, whereas SANS data demonstrate that 12-s-12 surfactants with 6 <= s <= 12 form rather small spheroidal micelles rather than strictly spherical micelles. By means of comparing our present SANS results with previously determined growth rates using time-resolved fluorescence quenching, we are able to conclude that micelles formed by 12-6-12, 12-8-12, 12-10-12, and 12-12-12 are shaped as oblate rather than prolate spheroids. As a result, our present investigation suggests a never before reported structural behavior of Gemini surfactant micelles, according to which micelles transform from elongated ellipsoids to nonelongated oblate spheroids as the length of the spacer group is increased. The aggregation number of oblate micelles is observed to monotonously decrease with an increasing length of the surfactant spacer group, mainly as a result of a decreasing minor half axis (a), whereas the major half axis (b) is rather constant with respect to s. We argue that geometrically heterogeneous elongated micelles are formed by dimeric surfactants with a short spacer group mainly as a result of the surface charges becoming less uniformly distributed over the micelle interface. As the length of the spacer group increases, the distance between intramolecular charges become approximately equal to the average distance between charges on the micelle interface, and as a result, rather small oblate spheroidal micelles with a more uniform distribution of surface charges are formed by dimeric 12-s-12 surfactants with 6 <= s <= 12.

  • 6.
    Bergström, L. Magnus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Skoglund, Sara
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Danerlöv, Katrin
    Garamus, Vasil M.
    Pedersen, Jan Skov
    The growth of micelles, and the transition to bilayers, in mixtures of a single-chain and a double-chain cationic surfactant investigated with small-angle neutron scattering2011Inngår i: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 7, nr 22, s. 10935-10944Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Self-assembly in aqueous mixtures of a single-chain (DTAB) and a double-chain cationic surfactant (DDAB) has been investigated with small-angle neutron scattering (SANS). Small oblate spheroidal micelles formed by DTAB grow with respect to width and length to form mixed ellipsoidal tablet-shaped micelles as an increasing fraction of DDAB is admixed into the micelles. The growth behaviour of the micelles is rationalized from the general micelle model in terms of three bending elasticity constants spontaneous curvature (H(0)), bending rigidity (k(c)) and saddle-splay constant ((k(c)) over bar kc). It is found that micelles grow with respect to width, mainly as a result of decreasing k(c)H(0), and in the length direction as a result of decreasing k(c). The micelles are still rather small, i.e. about 140 angstrom in length, as an abrupt transition to large bilayer aggregates is observed. The micelle-to-bilayer transition is induced by changes in aggregate composition and is observed to occur at a mole fraction of DDAB equal to about x = 0.48 in D(2)O, which is a significantly higher value than previously observed for the same system in H(2)O (x = 0.41). An abrupt micelle-to-bilayer transition is in agreement with predictions from the general micelle model, according to which an abrupt transition from micelles to bilayers is expected to occur at xi H(0) = 1/4, where x is the thickness of the self-assembled interface, and we may conclude that H(0)(D(2)O) > H(0)(H(2)O) for the system DDAB/DTAB in absence of added salt. Samples with bilayers are found to be composed of bilayer disks coexisting with vesicles. Disks are found to always predominate over vesicles with mass fractions about 70-90% disks and 10-30% vesicles. Micelles, disks and vesicles are observed to coexist in a few samples close to the micelle-to-bilayer transition.

  • 7.
    Bergström, L. Magnus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Skoglund, Sara
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Edwards, K.
    Eriksson, J.
    Grillo, I.
    Self-assembly in mixtures of an anionic and a cationic surfactant: A comparison between small-angle neutron scattering and cryo-transmission electron microscopy2013Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, nr 38, s. 11834-11848Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The self-assembly in SOS-rich mixtures of the anionic surfactant sodium octyl sulfate (SOS) and the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) has been investigated with the complementary techniques small-angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM). Both techniques confirm the simultaneous presence of open and closed bilayer structures in highly diluted samples as well as the existence of small globular and large elongated micelles at higher concentrations. However, the two techniques sometimes differ with respect to which type of aggregates is present in a particular sample. In particular, globular or wormlike micelles are sometimes observed with cryo-TEM in the vicinity of the micelle-to-bilayer transition, although only bilayers are present according to SANS and the samples appear bluish to the eye. A similar discrepancy has previously been reported but could not be satisfactorily rationalized. On the basis of our comparison between in situ (SANS) and ex situ (cryo-TEM) experimental techniques, we suggest that this discrepancy appears mainly as a result of the non-negligible amount of surfactant adsorbed at interfaces of the thin sample film created during the cryo-TEM specimen preparation. Moreover, from our detailed SANS data analysis, we are able to observe the unusually high amount of free surfactant monomers present in SOS-rich mixtures of SOS and CTAB, and the experimental results give excellent agreement with model calculations based on the Poisson-Boltzmann mean field theory. Our careful comparison between model calculations and experiments has enabled us to rationalize the dramatic microstructural transformations frequently observed upon simply diluting mixtures of an anionic and a cationic surfactant.

  • 8.
    Bergström, L. Magnus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Skoglund, Sara
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Edwards, Katarina
    Eriksson, Jonny
    Grillo, Isabelle
    Spontaneous Transformations between Surfactant Bilayers of Different Topologies Observed in Mixtures of Sodium Octyl Sulfate and Hexadecyltrimethylammonium Bromide2014Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, nr 14, s. 3928-3938Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of adding salt on the self-assembly in sodium octyl sulfate (SOS)-rich mixtures of the anionic surfactant SOS and the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) have been investigated with the two complementary techniques, small-angle neutron scattering (SANS) and cryo-transmission electron microscopy. We are able to conclude that addition of a substantial amount of inert salt, NaBr, mainly has three effects on the structural behaviors: (i) the micelles become much larger at the transition from micelles to bilayers, (ii) the fraction of bilayer disks increases at the expense of vesicles, and (iii) bilayer aggregates perforated with holes are formed in the most diluted samples. A novel form factor valid for perforated bilayer vesicles and disks is introduced for the first time and, as a result, we are able to directly observe the presence of perforated bilayers by means of fitting SANS data with an appropriate model. Moreover, we are able to conclude that the morphology of bilayer aggregates changes according to the following sequence of different bilayer topologies, vesicles --> disks --> perforated bilayers, as the electrolyte concentration is increased and surfactant mole fraction in the bilayer aggregates approaches equimolarity. We are able to rationalize this sequence of transitions as a result of a monotonous increase of the bilayer saddle-splay constant ((k) over bar (bi)(c)) with decreasing influence from electrostatics, in agreement with theoretical predictions as deduced from the Poisson-Boltzmann theory.

  • 9. Bergström, Lars Magnus
    Bending elasticity of charged surfactant layers: The effect of layer thickness2006Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, nr 8, s. 3678-3691Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The bending properties of charged one-component surfactant films of finite thickness have been theoretically investigated. It is demonstrated that finite thickness effects are of crucial importance for layers formed by an ionic surfactant with a flexible hydrophobic tail, whereas the influence on layers formed by a surfactant with a rigid tail is less pronounced. As a matter of fact, in the former case, the spontaneous curvature and mean and Gaussian bending constants all become significantly modified as compared to an infinitely thin surface and assume identical values as if the surfactant layer were bent at constant layer thickness. As a result, the spontaneous curvature is found to decrease, whereas the magnitudes of the mean and Gaussian bending constants both increase with increasing layer thickness as well as with increasing hydrophobic-hydrophilic interfacial tension. All of these trends are consistent with experimental observations. In addition, it is demonstrated that separating the hydrophilic-hydrophobic interface and the surface of charge a certain distance from each other tends to increase the spontaneous curvature and the mean bending constant, whereas the Gaussian bending constant becomes increasingly negative. It is also found that the work of bending a bilayer into a geometrically closed vesicle is substantially raised to large positive values for surfactants with flexible aliphatic chains, whereas the corresponding quantity is negative for surfactants with rigid tails, indicating that stable bilayer structures may only be formed by the former surfactant. Furthermore, each of the bending elasticity constants for monolayers formed by a double-chain ionic surfactant are found to assume lower values as compared with layers formed by the corresponding single-chain surfactant.

  • 10. Bergström, Lars Magnus
    Bending elasticity of charged surfactant layers: The effect of mixing2006Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, nr 16, s. 6796-6813Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Expressions have been derived from which the spontaneous curvature (H-0), bending rigidity (k(c)), and saddle-splay constant ((k) over bar (c)) of mixed monolayers and bilayers may be calculated from molecular and solution properties as well as experimentally available quantities such as the macroscopic hydrophobic-hydrophilic interfacial tension. Three different cases of binary surfactant mixtures have been treated in detail: (i) mixtures of an ionic and a nonionic surfactant, (ii) mixtures of two oppositely charged surfactants, and (iii) mixtures of two ionic surfactants with identical headgroups but different tail volumes. It is demonstrated that k(c)H(0), k(c), and (k) over bar

  • 11.
    Bergström, Lars Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    Bending Elasticity of Nonionic Surfactant Layers2009Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, nr 4, s. 1949-1960Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A novel approach to evaluate the bending elasticity of monolayers formed by nonionic surfactants with a rigid head group is introduced by means of considering head group repulsion as derived from the free energy of mixing rigid hydrophilic head groups with surrounding solvent molecules as well as contributions related to the hydrophobic tails. Explicit expressions for the spontaneous curvature (H-0), bending rigidity (k(c)) and saddle-splay constant ((k) over bar (c)) have been derived for the constraint of constant chemical potential of free surfactant (thermodynamically open layers) as well as the constraint of constant aggregation number (thermodynamically closed layers). Most interestingly, it is demonstrated that k(c) for thermodynamically open layers formed by a nonionic surfactant with rigid tail and head group always must be zero. However, k(c) for surfactants with a flexible tail as a function of the head group-to-tail volume ratio is found to go through a maximum at some large, positive value of k(c) and H-0 approximate to 0. Eventually, k(c) falls below zero as the head group volume increases above a certain value. Hence, we may conclude that nonionic surfactants with a rigid head group may form thermodynamically stable fluid layers or aggregates only insofar the hydrophobic part is flexible with respect to chain conformational. degrees of freedom and the head group is not too voluminous. It is found that the head group repulsion contribution to k(c)H(0) is always positive whereas the corresponding contribution to (k) over bar

  • 12. Bergström, Lars Magnus
    Bending energetics of tablet-shaped micelles: A novel approach to rationalize micellar systems2007Inngår i: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 8, nr 3, s. 462-472Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A novel approach to rationalize micellar systems is expounded in which the structural behaviour of tablet-shaped micelles is theoretically investigated as a function of the three bending elasticity constants: spontaneous curvature (H-0), bending rigidity (k(c)), and saddle-splay constant (k(c)). As a result, experimentally accessible micellar properties, such as aggregation number, length-to-width ratio, and polydispersity, may be relation to the different bending elasticity constants. Is it demonstrated that discrete micelles or connected cylinders form when H-0 > 1/4 xi where xi is the thickness of a surfacant monolayer, whereas various bilayer structures are expected to predominate when H-0 > 1/4 xi. Our theory predicts, in agreement with experiments, a transition from discrete globular (tablet-shaped) micelles to a phase of ordered, or disordered, connected cylinders above a critital surfactant concentration. Moreover, a novel explanation for the mechanism of growth, from small globular to long rodlike or wormlike micelles, follows as a consequence from the theory. In accordance, polydiperse elongated micelles (large length-to-width ratio) for as the bending rigidity is lowered, approaching the critical point at k(c) - 0, whereas monodisperse globular micelles (small length-to-width ratio) are expected to be present at larg k(c) values. The spontaneous curvature mainly determines the width of tablet-shaped or ribbonlike micelles, or the radius of dislike micelles, whereas the saddle-splay constant primarily influences the size but not the shape of the micelles.

  • 13.
    Bergström, Lars Magnus
    KTH, Tidigare Institutioner                               , Kemi.
    Derivation of expressions for the spontaneous curvature, mean and Gaussian bending constants of thermodynamically open surfactant monolayers and bilayers2003Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 118, nr 3, s. 1440-1452Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have derived expressions for the spontaneous curvature H-0, the mean and Gaussian bending constants, k(c) and (k) over bar (c), respectively, for a surfactant film of finite thickness that is open in a thermodynamic sense. Geometrical packing constraints are taken into account and give rise to explicit large and important contributions to k(c), (k) over bar (c), and k(c)H(0). From its contribution to the latter quantity we may deduce that surfactant aggregates (micelles, vesicles, microemulsion droplets) are expected to dramatically increase their size with increasing surfactant tail length. Moreover, the coupling between free energy contributions related to surfactant head group and tail with geometrical packing constraints give rise to dominant terms on the form 2xi(p)H(0), where xi(p) is the thickness of a planar film, in the expressions for k(c). In the case of repulsive head group effects that favor a large spontaneous curvature, such as electrostatics, these terms raise k(c) and thus increase the rigidity of the film. Due to the constraint of constant free monomer chemical potentials, the composition of the film becomes a function of curvature. As a result, the ability of a surfactant film to have different surfactant compositions in differently curved parts (e.g., inner and outer layer of a vesicle, central parts and end caps of rod or threadlike micelles, etc.) may considerably reduce k(c), whereas (k) over bar

  • 14.
    Bergström, Lars Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Influence of bending energetics on the size, shapeand polydispersity of droplet microemulsions2008Inngår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 316, s. 15-26Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A theory for ellipsoidal shape fluctuating droplet microemulsions in the presence of excess discrete phase (Winsor I and II) is expounded that combines bending energetics of the amphiphilic monolayer at the droplet interface with thermodynamics of self-assembling solute and amphiphilic molecules. The theory relates the three bending elasticity constants spontaneous curvature (H0), bending rigidity (kc) and saddle-splay constant () with interfacial tension, average size and shape and polydispersity of microemulsion droplets. It is demonstrated that the well-known conventional relations become modified as the entropy of self-assembling amphiphilic as well as solute molecules are taken into account, in particular at low values of the effective bending constant . As a result, the average droplet radius 〈R〉 as well as the droplet polydispersity σR/〈R〉 behave consistently in the limit whereas the conventional expressions are recovered in the limit . It is demonstrated that association entropy effects may be quantified by a parameter kS with same dimension and order of magnitude as kc and . kS is found to be always negative and tends to decrease 〈R〉 and to increase σR/〈R〉. Moreover, the average axial ratio of an oblate/prolate fluctuating droplet is found to be a strong function of the bending rigidity (the droplets become increasingly non-spherical with decreasing kc) but is independent of , in contrast to previous investigations where association entropy effects were neglected.

  • 15. Bergström, Lars Magnus
    Model calculations of the spontaneous curvature, mean and Gaussian bending constants for a thermodynamically open surfactant film2006Inngår i: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 293, nr 1, s. 181-193Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The spontaneous curvature (H-0), mean and Gaussian bending constants (k(c) and $(k) over bar $ (c)), as defined in the well-known Helfrich expression, have been calculated from a detailed model for a thermodynamically open surfactant layer. The effect of head group cross-section area, surfactant tail length and electrolyte concentration for monovalent ionic surfactants have been investigated. Geometrical packing constraints subjected to the aggregated hydrocarbon tails and electrostatics are found to be the dominant contributions to H-0, k(c) and (k) over bar (c). In addition, the transition from spherocylindrical micelles to vesicles were investigated in terms of the three parameters and the following simple expressions were derived as criteria for coexistence between micelles and vesicles H-0 = 1/4 xi and < N >(ves)/< N >(mic) = exp[4 pi(k(c) + (k) over bar (c))/kT], where xi is the thickness of the hydrocarbon part of the film and < N >(mic) and < N >(ves) the average aggregation numbers of micelles and vesicles, respectively. However, it is found that the ratio < N >(ves)/< N >(mic) is order of magnitudes too large for vesicles to form at all in charged single-surfactant systems where the surfactant head is of moderate size.

  • 16.
    Bergström, Lars Magnus
    KTH, Tidigare Institutioner                               , Kemi.
    Molecular interpretation of the mean bending constant for a thermodynamically open vesicle bilayer2001Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, nr 24, s. 7675-7686Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Expressions for the various molecular contributions to the mean bending constant k(c) of a thermodynamically open vesicle bilayer have been derived, from which k(c) maybe calculated from an appropriate molecular-thermodynamic model as a function of the structure of the surfactants making up the aggregates as well as the solution state. It is demonstrated that k(c) determines the shape of a vesicle bilayer insofar as spherical vesicles form when k(c) is large and positive! whereas nonspherical. vesicles predominate at values of k(c) close to or below zero. It is found that contributions due to electrostatics and residual headgroup effects, which are present for one-component as well as mixed aggregates, mainly give rise to a positive value of k(c) whereas geometrical packing constraints are less important. However, the mixing of two or more surfactants can significantly reduce k(c) to values where nonspherical vesicles may begin to form. The magnitude of the reduction of k(c) due to mixing increases with increasing asymmetry with respect to headgroup cross-section area, charge number, and hydrocarbon tail volume between two surfactants in a binary surfactant mixture. The asymmetry is most pronounced for a binary mixture where the surfactant that carries the charge has the larger headgroup and the smaller tail. The reduction of k(c) due to mixing is, however, expected to be less than the corresponding effect for the bilayer bending constant of a spherical vesicle as a result of an additional positive contribution in the expression for the compositional contribution to k(c).

  • 17.
    Bergström, Lars Magnus
    KTH, Tidigare Institutioner                               , Kemi.
    Synergistic effects in mixtures of an anionic and a cationic surfactant2001Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, nr 4, s. 993-998Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Synergistic effects in mixtures of an anionic and a cationic surfactant have been theoretically investigated. We derive an explicit expression far the critical micelle concentration (cmc) as a function of the aggregate composition from the Poisson-Boltzmann mean field theory and, thus, demonstrate that the conspicuously large synergistic effects that have been experimentally observed can be rationalized without the need of invoking any specific interactions between the surfactant headgroups. The simple relation beta = -4 epsilon (el/kTelNzT) is derived, i.e.,the interaction parameter beta is directly related to the electrostatic free energy contribution epsilon (el) for the pure surfactant, implying, among other things, that the magnitude of beta decreases vith increasing cmc for the pure surfactant in agreement with experimental observations. We furthermore demonstrate that the aggregate composition is close to equimolar composition (x(1) = 0.5) at cmc in almost the entire regime of overall surfactant compositions and that the free monomer concentration of the surfactant in excess is generally much larger than the corresponding quantity for the surfactant in deficit.

  • 18.
    Bergström, Lars Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    Thermodynamics and bending energetics of toruslike micelles2008Inngår i: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 327, nr 1, s. 191-197Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The self-assembly of surfactants forming toruslike or toroidal micelles has been investigated from a theoretical point of view, in particular the structural behaviour and stability of tori in terms of the three bending elasticity constants spontaneous curvature (H-0), bending rigidity (k(c)) and saddle-splay constant (kc). It is demonstrated that the size of toruslike micelles increases with an increasing bending rigidity, but is independent of both spontaneous Curvature and saddle-splay constant. Similar to conventional micelles, toruslike micelles are found to be stable over bilayers as the spontaneous curvature times the surfactant layer thickness exceeds 1/4. Moreover, it is shown that toruslike micelles, in general, are favoured at the expense of long spherocylindrical micelles as a result of elimination of the unfavourable end-caps. However, conventional micelles that are able to grow with respect to both width and length (tablets) may be stable over tori as well as spheres in much wider regimes of different bending elasticity constants. As a result, toruslike micelles are predicted to be stable over conventional micelles, including rods, at large values of the effective bending constant k(eff) equivalent to 2k(c) +(k) over bar (c), i.e. in the same region where infinite cylinders are expected to be observed. This result is consistent with the fact that toruslike micelles have usually been observed to coexist with large networks of branched cylinders.

  • 19.
    Bergström, Lars Magnus
    KTH, Tidigare Institutioner                               , Kemi.
    Thermodynamics of anisotropic surfactant micelles. I. The influence of curvature free energy on the micellar size and shape2000Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 113, nr 13, s. 5559-5568Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A novel theory for the structural behavior of surfactant micelles is expounded. The micelles are considered to be generally shaped as triaxial tablets with distinct thickness width and length, respectively, and may become spherical, spherocylindrical or disk-shaped in the special cases where two or more of the dimensions are equal. It is demonstrated that the average width and length of a tablet-shaped micelle with a fixed thickness is mainly determined by two constants, k(1) and k(2), related to the first and second order correction in curvature of the micellar end caps. The size of the micelles is found to be mainly determined by k(1), whereas k(2) influences the shape, i.e., the length-to-width ratio, of the micelles so that the micellar size increases with increasing k(1) and the length-to-width ratio decreases with increasing k(2). Hence, large positive values of k(2) promote the formation of tablets rather than very long spherocylinders. An additional parameter related to the curvature of the straight cylindrical rims may influence the structure of the tablet-shaped micelles insofar k(2) is close to or below zero.

  • 20.
    Bergström, Lars Magnus
    KTH, Tidigare Institutioner                               , Kemi.
    Thermodynamics of anisotropic surfactant micelles. II. A molecular interpretation of the micellar curvature free energy2000Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 113, nr 13, s. 5569-+Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Explicit expressions have been derived for the two curvature constants k(1) and k(2) that mainly influence the size and shape, respectively, of generally shaped micelles (triaxial tablets with a thickness < width < length). It is found that geometrical packing constraints, together with an unfavorable hydrocarbon/water interfacial tension gamma(hc/w), give rise to a large and positive contribution to both k(1) and k(2) that increases with the micellar thickness (equivalent to surfactant tail length) as well as with gamma(hc/w). The constant k(1) that mainly influence the size of the micelles may be brought down by electrostatics to values where rather small micelles are able to form. However, electrostatics also have a tendency to increase the constant k(2) that mainly affects the length-to-width ratio of the micelles so that the smaller micelles are predicted to be rather disklike, i.e., with a low length-to-width ratio. In addition, residual head group effects as well as the free energy contribution due to the hydrocarbon chains may influence the micellar size and shape. In particular, it is demonstrated that mixing of two surfactants reduces k(2) and promotes the formation of elongated micelles with a large length-to-width ratio whereas k(1), and thus the overall size of the micelles, is only slightly influenced. The effect of mixing is predicted to increase with increasing asymmetry between the surfactants mixed in the micelles with respect to head group size and charge number as well as hydrophobic tail volume.

  • 21.
    Bergström, Lars Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Thermodynamics of Self-Assembly2011Inngår i: Application of Thermodynamics to Biological and Materials Science: Chapter 11, InTech, 2011, s. 289-314Kapittel i bok, del av antologi (Annet vitenskapelig)
  • 22.
    Bergström, Lars Magnus
    KTH, Tidigare Institutioner                               , Kemi.
    Thermodynamics of unilamellar vesicles: Influence of mixing on the curvature free energy of a vesicle bilayer2001Inngår i: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 240, nr 1, s. 294-306Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of mixing on the curvature free energy of a thermodynamically open, reversibly formed vesicle bilayer is investigated by deriving expressions for the various contributions to the Mayer bending constant k(bi) as functions of the structure of aggregated surfactants as well as the solution state (electrolyte concentration, average composition in the bilayers, etc). k(bi) is shown to be lowered in surfactant mixtures as a result of the fact that a mixed vesicle bilayer that is open in the thermodynamic sense may assume different compositions in the inner and outer monolayers. The net contribution of all terms related to surfactant mixing is to lower k(bi). The magnitude of this reduction increases with increasing asymmetry between the two surfactants with respect to charge number, head group size, and tail length. The reduction of k(bi) due to mixing is most pronounced for mixtures where the surfactant that carries charge or has the highest charge number has the larger head group and the smaller tail.

  • 23.
    Bergström, Lars Magnus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    Bramer, Tobias
    Synergistic effects in mixtures of oppositely charged surfactants as calculated from the Poisson-Boltzmann theory: A comparison between theoretical predictions and experiments2008Inngår i: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 322, nr 2, s. 589-595Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Critical micelle concentrations in mixtures of an anionic surfactant and a cationic amphiphilic drug have been investigated using a model-independent procedure to quantify observed synergistic effects. Experimental results were compared with a theory based on the Poisson-Boltzmann mean field approximation of a charged interface with a diffuse layer of counterions. Explicit expressions for the activity coefficients from which the critical micelle concentration can be calculated and quantitatively predicted have been derived and excellent agreement between experimental data and theory was obtained. As a result, we demonstrate that it is possible to rationalize and predict the magnitude of synergism in mixtures of oppositely charged surfactants in the presence of added salt.

  • 24.
    Bergström, Lars Magnus
    et al.
    KTH, Tidigare Institutioner                               , Kemi.
    Eriksson, J. C.
    A theoretical analysis of synergistic effects in mixed surfactant systems2000Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, nr 18, s. 7173-7181Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Synergistic effects in mixed binary surfactant systems have been investigated by analyzing the main contributions to the free energy of forming a mixed surfactant aggregate. We show that a nonlinear behavior of the critical micelle concentration (cmc) with respect to the surfactant composition of the aggregates is determined by a nonlinear behavior of the free energy per aggregated surfactant. It appears that synergistic effects are due mainly to entropic free energy contributions related with the surfactant headgroups. For a mixture of a monovalent ionic and a nonionic surfactant in the absence of added salt we obtain, entirely because of electrostatic reasons, a negative deviation from ideal behavior of the cmc vs the aggregate composition corresponding to an interaction parameter beta approximate to -1, whereas beta values on the order of -5 or even less can arise for mixtures of two ionic surfactants with the same charge number but with different hydrocarbon moieties. Moreover, we introduce a novel expression for the free energy of mixing aggregated surfactant headgroups with surrounding solvent molecules. Accordingly, synergistic effects arise as a result of different headgroup cross-section areas in mixtures of two nonionic surfactants with rigid headgroups. These effects are found to be rather small, with 0 > beta > -1, when the difference in headgroup size is modest but can become more significant when the size difference is larger. In mixtures of an ionic and a nonionic surfactant with different headgroup cross-section areas the two contributions to synergistic effects always enhance one another and, hence, beta values below -1 are obtained. Generally, the synergistic effects tend to increase with increasing asymmetry between the two surfactants.

  • 25.
    Bergström, Lars Magnus
    et al.
    KTH, Tidigare Institutioner, Kemi. YKI, Institute for Surface Chemistry, Sweden .
    Eriksson, Jan Christer
    KTH, Tidigare Institutioner, Kemi. YKI, Institute for Surface Chemistry, Sweden .
    Synergistic effects in binary surfactant mixtures2004Inngår i: Progress in Colloid and Polymer Science, ISSN 0340-255X, E-ISSN 1437-8027, Vol. 123, s. 16-22Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    By considering the main contributions to the micellar free energy we have analysed the synergistic effect often seen on the CMC of a binary surfactant mixture. The synergistic effects are due mainly to the entropic free energy contributions related with the surfactant head groups. Several cases have been treated: (i) For a mixture of a monovalent ionic and a non-ionic surfactant in the absence of added salt we obtain, entirely because of electrostatic reasons, a negative deviation from the ideal behaviour corresponding to an interaction parameter β≈-1. Upon adding an inert salt we found that the magnitude of the synergistic effect first increases, reaches a maximum and eventually decreases. (ii) For mixtures of two ionic surfactants with the same charge number but with different hydrocarbon moieties β-values as low as -10 may arise. (iii) For mixtures of an anionic and a cationic surfactant enormous effects are anticipated yielding β≤-20 depending on the CMCs of respective pure surfactant. (iv) Synergistic effects due to different cross-section areas of the head groups are found to be rather small, with 0 > β > -1, provided the difference in head group size is modest but can become more significant when the size difference is larger.

  • 26.
    Bergström, Lars Magnus
    et al.
    KTH, Tidigare Institutioner                               , Kemi.
    Jonsson, P.
    Persson, M.
    Eriksson, J. C.
    A model-independent evaluation of experimental data, and comparison with theory, of synergistic effects in mixtures of an ionic and a nonionic surfactant2003Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 19, nr 26, s. 10719-10725Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Critical micelle concentrations for mixtures of an anionic (sodium dodecyl sulfate) and a nonionic (decyl beta-glucoside) surfactant was obtained from surface tension measurements at different concentrations of added NaCl. The observed synergistic effects were analyzed by means of introducing a novel model-independent synergy parameter. The model-independent evaluation has enabled the comparison of experimental results with a theoretical model based on the Poisson-Boltzmann (PB) mean field theory for spherical, cylindrical, and planar geometries, respectively. We found that best agreement with experimental data was obtained for largely curved structures (spherical and cylindrical micelles) at all [NaCl], which is consistent with the fact that rather small micelles, as a rule, form at the critical micelle concentration. Moreover, the PB theory was found to better describe synergistic behavior of the experimental data than the more conventional regular mixture theory, in particular at low electrolyte concentrations. The magnitude of the observed synergistic effects was found to increase as a small amount of NaCl was added and reach a maximum at [NaCl] = 10 mM, in agreement with the PB theory. As expected, synergism was observed to decrease in magnitude upon further addition of NaCl.

  • 27.
    Bergström, Lars Magnus
    et al.
    KTH, Tidigare Institutioner, Kemi.
    Kjellin, Mikael
    KTH, Tidigare Institutioner, Kemi.
    Claesson, Per M.
    KTH, Tidigare Institutioner, Kemi.
    Grillo, I.
    Small-angle neutron scattering study of mixtures of cationic polyelectrolyte and anionic surfactant: Effect of polyelectrolyte charge density2004Inngår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 108, nr 6, s. 1874-1881Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have studied mixtures of an anionic surfactant (deuterated sodium dodecyl sulfate, SDS-d) and cationic polyelectrolytes with different charge densities (10%, 30%, 60%, and 100%) using small-angle neutron scattering (SANS). Near compositions corresponding to charge neutralization, the solutions phase separate into a complex phase (precipitate) consisting of, in the cases of 30%, 60%, and 100% charge density, a two-dimensional (213) hexagonal lattice of close-packed cylindrical micelles and a clear liquid. When either polyelectrolyte with charge density less than 100% or SDS-d is present in sufficient excess, the solution becomes clear and isotropic, and from the scattering data we may conclude that prolate or rod-shaped micelles are present. The micelles are seen to grow in length with increasing SDS-d concentration and polyelectrolyte charge density from about 80 Angstrom to 550 Angstrom, whereas the cross-sectional radius is 15 Angstrom and approximately constant. The number of micelles per polyelectrolyte chain is found to be slightly larger than unity (1-6). In some of the (turbid) samples rod-shaped micelles are found to coexist with larger polyelectrolyte-surfactant complexes. Solutions consisting of 10% charged polyelectrolyte and SDS-d are very viscous and gellike, and the complex phase is much less defined with a much larger distance between adjacent aggregates in the complex phase.

  • 28.
    Bergström, Lars Magnus
    et al.
    KTH, Tidigare Institutioner                               , Kemi.
    Kjellin, U. R. M.
    Claesson, Per M
    KTH, Tidigare Institutioner                               , Kemi.
    Pedersen, J. S.
    Nielsen, M. M.
    A small-angle X-ray scattering study of complexes formed in mixtures of a cationic polyelectrolyte and an anionic surfactant2002Inngår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 106, nr 44, s. 11412-11419Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The internal structure of the solid phase formed in mixtures of the anionic surfactant sodium dodecyl sulfate (SDS) and a range of oppositely charged polyelectrolytes with different side chains and charge density has been investigated using small-angle X-ray scattering. Polyelectrolytes with short side chains ([3-(2-methylpropionamido)propyl]trimethylammonium chloride, MAPTAC, and poly{[(2-propionyloxy)ethyl]-trimethylammonium chloride}, PCMA) form a 2-dimensional hexagonal structure with SDS, whereas a polyelectrolyte without side chains (poly(vinlyamine), PVAm) forms a lamellar structure. The hexagonal structure of MAPTAC is retained either when a neutral monomer (acrylamide, AM) is included in the polymer backbone to reduce the charge density or when a nonionic surfactant is admixed to the SDS/polyelctrolyte complex.. The unit cell length of AM-MAPTAC increases with decreasing charge density from a=47.7 Angstrom (MAPTAC, 100% charge density) to 58.5 Angstrom (AM-MAPTAC, 30% charge density). The unit cell length in the lamellar SDS/PVAm complex (a=36.1 Angstrom) is significantly smaller than for the different hexagonal structures. It is conjectured that the cylinders in the hexagonal structure and the bilayers in the lamellar structure are based on self-assembled surfactant aggregates with the polyelectrolyte mainly located in the aqueous region adjacent to the charged surfactant headgroups.

  • 29.
    Bergström, Lars Magnus
    et al.
    KTH, Tidigare Institutioner                               , Kemi.
    Pedersen, J. S.
    A small-angle neutron scattering study of surfactant aggregates formed in aqueous mixtures of sodium dodecyl sulfate and didodecyldimethylammonium bromide2000Inngår i: Journal of Physical Chemistry B, ISSN 1089-5647, Vol. 104, nr 17, s. 4155-4163Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The structure of aggregates formed in aqueous mixtures of a single-chain anionic surfactant, sodium dodecyl sulfate (SDS), and a double-chain cationic surfactant, didodecyldimethylammonium bromide (DDAB), has been investigated at 38 degrees C using small-angle neutron scattering (SANS). Several overall surfactant concentrations [SDS] + [DDAB] between 0.1 and 5 wt % were measured at the two SDS-rich compositions [SDS]:[DDAB] = 90:10 and 95:5. Samples with a concentration above about [SDS] + [DDAB] = 1 wt % at [SDS]:[DDAB] = 95:5 contained only somewhat elongated tablet-shaped micelles (triaxial ellipsoids) with typical values of the half-axes a (related to the thickness) = 14 Angstrom, b (related to the width) = 23 Angstrom, and c (related to the length) = 27 Angstrom. When a sample at [SDS]:[DDAB] = 95:5 is diluted below about [SDS] + [DDAB] = 1 wt %, an increasing amount of small unilamellar vesicles forms, and in the samples below about 0.2 wt %, only vesicles are observed. The average radius of the vesicles [R] increases from about 90 Angstrom at 0.3 wt % to 110 Angstrom at 0.1 wt %. The transition from micelles to vesicles with decreasing surfactant concentration was also observed in the samples at [SDS]:[DDAB] = 90:10 in which, however, an additional amount of bilayer sheets was seen to be always present. Compared with the micelles at [SDS]:[DDAB] = 95:5, the micelles formed at [SDS]:[DDAB] = 90:10 were considerably longer (c approximate to 40 Angstrom), but with similar cross section dimensions, and the vesicles formed were seen to be somewhat larger than the corresponding aggregates at 95:5. The relative standard deviation sigma(R)/[R] of the (number-weighted) vesicle size distributions was in the range 0.2 < sigma(R)/[R] < 0.3.

  • 30.
    Bergström, Lennart Magnus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Grillo, I.
    Correlation between the geometrical shape and growth behaviour of surfactant micelles investigated with small-angle neutron scattering2014Inngår i: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 10, nr 46, s. 9362-9372Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The correlation between the growth behaviour and geometrical shape for CTAB-rich mixed micelles formed by the cationic surfactant hexadecyl trimethyl ammonium bromide (CTAB) and the anionic surfactant sodium octyl sulphate (SOS) has been investigated with small-angle neutron scattering (SANS). Small tablet-shaped micelles formed by CTAB are found to grow only weakly in size with increasing surfactant concentration. The extent of growth becomes increasingly stronger as the fraction of SOS is increased. At higher fractions of SOS, a rather weak growth at low surfactant concentrations is followed by a sharp increase in aggregation numbers beyond a certain surfactant concentration. Such an abrupt transition from weakly to strongly growing micelles has been observed in the past for several micellar systems and is usually referred to as the second critical micelle concentration. The growth behaviour has been rationalized from a theoretical point of view by means of employing the recently developed general micelle model. The theory excellently predicts micellar growth behaviours as well as the observed correlation between the geometrical shape and micellar growth. In accordance, both width and length are found to slightly increase for weakly growing tablet-shaped micelles. On the other hand, strongly growing micelles that are observed above the second cmc display a completely different behaviour, according to which the length increases considerably while the width of the micelles decreases. Most interestingly, by means of optimizing the agreement between the general micelle model and experimentally determined aggregation numbers, we are able to determine the three bending elasticity constants: spontaneous curvature, bending rigidity and saddle-splay constant.

  • 31.
    Bergström, Lennart Magnus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Tehrani-Bagha, A.
    Nagy, G.
    Growth behavior, geometrical shape, and second CMC of micelles formed by cationic gemini esterquat surfactants2015Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, nr 16, s. 4644-4653Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Micelles formed by novel gemini esterquat surfactants have been investigated with small-angle neutron scattering (SANS). The growth behavior of the micelles is found to differ conspicuously depending on the length of the gemini surfactant spacer group. The gemini surfactant with a long spacer form rather small triaxial ellipsoidal tablet-shaped micelles that grow weakly with surfactant concentration in the entire range of measured concentrations. Geminis with a short spacer, on the other hand, form weakly growing oblates or tablets at low concentrations that start to grow much more strongly into polydisperse rodlike or wormlike micelles at higher concentrations. The latter behavior is consistent with the presence of a second CMC that marks the transition from the weakly to the strongly growing regime. It is found that the growth behavior in terms of aggregation number as a function of surfactant concentration always appear concave in weakly growing regimes, while switching to convex behavior in strongly growing regimes. As a result, we are able to determine the second CMC of the geminis with short spacer by means of suggesting a rather precise definition of it, located at the point of inflection of the growth curve that corresponds to the transition from concave to convex growth behavior. Our SANS results are rationalized by comparison with the recently developed general micelle model. In particular, this theory is able to explain and reproduce the characteristic appearances of the experimental growth curves, including the presence of a second CMC and the convex strongly growing regime beyond. By means of optimizing the agreement between predictions from the general micelle model and results from SANS experiments, we are able to determine the three bending elasticity constants spontaneous curvature, bending rigidity, and saddle-splay constant for each surfactant.

  • 32.
    Bergström, Magnus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Garamus, V. M.
    Structural behaviour of mixed cationic surfactant micelles: A small-angle neutron scattering study2012Inngår i: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 381, nr 1, s. 89-99Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Self-assembly in mixtures of two single-chain cationic surfactants, with different tail lengths (CTAB and DTAB) as well as of a single-chain (DTAB) and a double-chain (DDAB) cationic surfactant, with identical tail lengths, have been investigated with small-angle neutron scattering (SANS) and rationalised in terms of bending elasticity properties. The growth behaviour of micelles with respect to surfactant composition appears completely different in the two surfactant mixtures. DTAB form small oblate spheroidal micelles in presence of [NaBr]. =. 0.1. M that transform into prolate spheroidal mixed CTAB/DTAB micelles upon adding moderate amounts of CTAB, so as to give a mole fraction . y=. 0.20 in solution. Most unexpectedly, upon further addition of CTAB the mixed CTAB/DTAB micelles grow with an almost equal rate in both length and width directions to form tablets. In contrast to this behaviour, mixed DDAB/DTAB micelles grow virtually exclusively in the length direction, in presence of [NaBr]. =. 0.1. M, to form elongated ellipsoidal (tablet-shaped) and subsequently long wormlike micelles as the fraction of DDAB in the micelles increases. Mixed DDAB/DTAB micelles grow to become as long as 2000. å before an abrupt transition to large bilayer structures occurs. This means that the micelles are much longer at the micelle-to-bilayer transition as compared to the same mixture in absence of added salt. It is found that the point of transition from micelles to bilayers is significantly shifted towards higher fractions of aggregated DTAB as an appreciable amount of salt is added to DDAB/DTAB mixtures, indicating a considerable reduction of the spontaneous curvature with an increasing [NaBr]. By means of deducing the various bending elasticity constants from our experimental results, according to a novel approach by ours, we are able to conclude that the different growth behaviours appear as a consequence of a considerably lower bending rigidity, as well as higher saddle-splay constant, for DDAB/DTAB surfactant mixtures in presence of [NaBr]. =. 0.1. M, as compared to mixtures of CTAB/DTAB in [NaBr]. =. 0.1. M and DDAB/DTAB in absence of added salt.

  • 33.
    Bodvik, Rasmus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Dédinaité, Andra
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Karlson, Leif
    Bergström, Lars Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Baverback, Petra
    Pedersen, Jan Skov
    Edward, Katarina
    Karlsson, Göran
    Varga, Imre
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Claesson, Per M.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Aggregation and network formation of aqueous methylcellulose and hydroxypropylmethylcellulose solutions2010Inngår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 354, nr 1-3, s. 162-171Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Solution properties of methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) have been investigated as a function of temperature and concentration using a broad range of experimental techniques. Novelties include the extensive comparison between MC and HPMC solutions as well as the combination of techniques, and the use of Cryo transmission electron microscopy (Cryo-TEM). The correlation between rheology and light scattering results clearly demonstrates the relation between viscosity change and aggregation. Cryo-TEM images show the network structures formed. Viscosity measurements show that for both MC and HPMC solutions sudden changes in viscosity occur as the temperature is increased. The onset temperature for these changes depends on polymer concentration and heating rate. For both MC and HPMC solutions the viscosity on cooling is very different compared to on heating, demonstrating the slow equilibration time. The viscosity changes in MC and HPMC solutions are dramatically different; for MC solutions the viscosity increases by several orders of magnitude when a critical temperature is reached, whereas for HPMC solutions the viscosity decreases abruptly at a given temperature, followed by an increase upon further heating. Light and (SAXS) small-angle X-ray scattering shows that the increase in viscosity, for MC as well as for HPMC solutions, is due to extensive aggregation of the polymers. Light scattering also provides information on aggregation kinetics. The SAXS measurements allow us to correlate aggregation hysteresis to the viscosity hysteresis, as well as to extract some structural information. Cryo-TEM images give novel information that a fibrillar network is formed in MC solutions, and the strong viscosity increase occurs when this network spans the whole solution volume. For HPMC solutions the behaviour is more complex. The decrease in viscosity can be related to the formation of compact objects, and the subsequent increase to formation of fibrillar structures, which are more linear and less entangled than for MC.

  • 34.
    Claesson, Per M.
    et al.
    KTH, Tidigare Institutioner                               , Kemi.
    Bergström, Lars Magnus
    KTH, Tidigare Institutioner                               , Kemi.
    Dedinaite, Andra
    KTH, Tidigare Institutioner                               , Kemi.
    Kjellin, M.
    Legrand, J. F.
    Grillo, I.
    Mixtures of cationic polyelectrolyte and anionic surfactant studied with small-angle neutron scattering2000Inngår i: Journal of Physical Chemistry B, ISSN 1089-5647, Vol. 104, nr 49, s. 11689-11694Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Small-angle neutron scattering (SANS) data for solutions containing a highly charged cationic polyelectrolyte and an anionic surfactant are presented. The scattering data were obtained in pure D2O, emphasizing the scattering from the polyelectrolyte, and in a H2O/D2O mixture that contrast matches the polyelectrolyte. In the absence of surfactant, a broad scattering peak due to the mesh size of the polyelectrolyte solution is the most characteristic feature. This peak moves to larger q-values (smaller distances) as the polyelectrolyte concentration is increased, as expected for a semidilute polyelectrolyte solution. Addition of a small amount of surfactant reduces and finally removes this peak. Instead a sharp diffraction peak appears at high q-values. This Bragg peak corresponds to a characteristic distance of 37-39 Angstrom, and it is observed when either the polyelectrolyte or the surfactant is contrast matched by the solvent. Once this peak has appeared, its position does not change when the surfactant concentration is increased. The intensity of the peak grows, however, until a stoichiometric polyelectrolyte-surfactant complex has been formed. The Bragg peak remains in excess surfactant solution. These results are discussed in relation to the structure of the polyelectrolyte-surfactant aggregates and in connection with recent results from surface force and turbidity measurements using the same polyelectrolyte-surfactant pair.

  • 35.
    Dedinaite, Andra
    et al.
    KTH, Tidigare Institutioner                               , Kemi.
    Claesson, Per M
    KTH, Tidigare Institutioner                               , Kemi.
    Bergström, Lars Magnus
    KTH, Tidigare Institutioner                               , Kemi.
    Polyelectrolyte-surfactant layers: Adsorption of preformed aggregates versus adsorption of surfactant to preadsorbed polyelectrolyte2000Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, nr 12, s. 5257-5266Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The character of adsorbed layers containing both polyelectrolyte and surfactant depends on the type of polyelectrolyte used and the surfactant concentrations, as demonstrated by several recent studies. However, the layer properties also depend on the experimental pathway. This shows that the adsorbed layers can be trapped in quasi-equilibrium states and that the true equilibrium is reached only after experimentally inaccessible time scales. This has to be kept in mind when comparing different results reported in the literature. The present article highlights these effects using a system consisting of a highly charged cationic polyelectrolyte, poly{(propionyloxy)ethyl}trimethylammonium chloride (PCMA), and an anionic surfactant, sodium dodecyl sulfate (SDS). The adsorbed layer properties were determined using mainly surface force measurements and atomic force microscope (AFM) imaging. We also present some small-angle neutron scattering data for bulk PCMA-SDS complexes formed between the polyelectrolyte and the surfactant. They demonstrate the presence of a characteristic correlation length of about 37-39 Angstrom. A similar characteristic length scale is also observed in some of the adsorbed layers, both employing the AFM and the surface force apparatus. It may be interpreted as the distance between surfactant loaded polyelectrolyte chains.

  • 36. Ericsson, C. A.
    et al.
    Soderman, O.
    Garamus, V. M.
    Bergström, Lars Magnus
    Ulvenlund, S.
    Effects of temperature, salt, and deuterium oxide on the self-aggregation of alkylglycosides in dilute solution. 2. n-Tetradecyl-beta-D-maltoside2005Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 21, nr 4, s. 1507-1515Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effects of salt, temperature, and deuterium oxide on the self-aggregation of n-tetradecyl-beta-D-maltoside (C(14)G(2)) in dilute solution have been investigated by static light scattering, dynamic light scattering (DLS), small-angle neutron scattering (SANS), tensiometry, and capillary viscometry. SANS data show that the micelles can be described as relatively flexible polymer-like micelles with an elliptical cross section, at least at temperatures between 35 and 50 degreesC. The micelles grow in one dimension with increasing temperature and concentration. DLS and viscometry data suggest that the micelle size reaches a maximum at 60-70 degreesC. Comparison of DLS data in D2O and H2O shows that the micelles are larger in the former case. The effect of salt on the micelle size was found to follow the Hofmeister series. Thus, at constant salt concentration, the micelle size decreases according to the sequence SO42- > Cl (-)> NO3 > I- > SCN-, where I- and SCN- act as salting-in anions. From tensiometric data, it can be concluded that the temperature effects on micelle morphology do not correlate directly with those on unimer solubility. Rather, the temperature effect on the hydrocarbon chain conformation seems to be decisive for the micelle morphology. At constant temperature, on the other hand, the effect of salt and deuterium isotope is attributable to changes in effective headgroup area, including intermolecular interactions and water of hydration.

  • 37. Ericsson, C. A.
    et al.
    Söderman, O.
    Garamus, V. M.
    Bergström, Lars Magnus
    KTH, Tidigare Institutioner, Kemi.
    Ulvenlud, S.
    Effects of temperature, salt, and deuterium oxide on the self-aggregation of alkylglycosides in dilute solution. 1. n-nonyl-beta-D-glucoside2004Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 20, nr 4, s. 1401-1408Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of salt, temperature, and deuterium oxide on the self-aggregation of n-nonyl-beta-D-glucoside (beta-C(9)G(1)) in dilute solution has been investigated by static and dynamic light scattering, neutron scattering, and tensiometry. Scattering data show that the micelles can be described as relatively stiff, elongated structures with a circular cross section. With a decrease of temperature, the micelles grow in one dimension, which makes it surprising that the critical micelle concentration (cmc) shows a concomitant increase. On the other hand, substitution of D2O for H2O causes a large increase in micelle size at low temperatures, without any appreciable effect on cmc. With increasing temperature, the deuterium effect on the micelle size diminishes. The effects of salt on the micelle size and cmc were found to follow the Hofmeister series. Thus, at constant salt concentration, the micelle size decreased according to the sequence SO42- > Cl- > Br- > NO3- > I- > SCN-, whereas the effect on cmc displays the opposite trend. Here, I- and SCN- are salting-in anions. Similarly, the effects of cations decrease with increasing polarizability in the sequence Li-divided by > Na-divided by > K-divided by > Cs-divided by. At high ionic strength, the systems separate into two micellar phases. The results imply that the size of beta-C(9)G(1) micelles is extremely sensitive to changes in the headgroup size. More specifically, temperature and salt effects on effective headgroup size, including intermolecular interactions and water of hydration, are suggested to be more decisive for the micelle morphology than the corresponding effects on unimer solubility.

  • 38. Eriksson, J. C.
    et al.
    Bergström, Lars Magnus
    KTH, Tidigare Institutioner                               , Kemi.
    Persson, M.
    Solution thermodynamics of mixed nonionic/ionic and ionic/ionic surfactant micelles2003Inngår i: Russian Journal of Physical Chemistry, ISSN 0036-0244, E-ISSN 1531-863X, Vol. 77, s. S87-S94Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    By considering the main contributions to the composition-dependent free energy of mixed micelles and relying on the pseudophase approximation, we have devised new schemes for analyzing the synergistic effects often observed for the CMCs of binary surfactant mixtures. It turns out that merely free energy contributions (other than the one due to ideal mixing) which are nonlinear with respect to the surfactant composition in the micelles can give rise to synergism. Contrary to what is commonly presumed, the synergistic effects are to a large extent caused by entropic rather than energetic contributions to the head group free energy. Specifically, the following cases have been treated: (i) a mixture of a nonionic and an ionic surfactant with and without an excess of added salt and (ii) a mixture of two ionic surfactants, in all instances whilst making use of the standard Poisson-Boltzmann theory to account for the electrostatic free energies. The agreement with experimental CMC data for systems of this kind is satisfactory.

  • 39.
    Johansson, Emma
    et al.
    Department of Physical and Analytical Chemistry, Physical Chemistry, Uppsala University.
    Sandström, Maria C
    Department of Physical and Analytical Chemistry, Physical Chemistry, Uppsala University.
    Bergström, Lars Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Edwards, Katarina
    Department of Physical and Analytical Chemistry, Physical Chemistry, Uppsala University.
    On the Formation of Discoidal versus Threadlike Micelles in Dilute Aqueous Surfactant/Lipid Systems2008Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, nr 5, s. 1731-1739Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In a recent study, we showed that the surfactant 1,2-distearoyl-sn-glycero-3-phosphatidylethanolamine-N-[methoxy(polyethylene glycol)-2000 (DSPE-PEG2000) induced mixed micelles of either threadlike or discoidal shape when mixed with different types of lipids. In this study, we have exchanged the PEG−lipid for the more conventional surfactants octaethylene glycol monododecyl ether (C12E8), hexadecyltrimethylammonium bromide (CTAB), and sodium dodecyl sulfate (SDS). Cryo-TEM investigations show that also these surfactants are able to induce the formation of long-lived discoidal micelles. Generally, the preference for either discoidal or threadlike micelles can be tuned by the choice of lipids and environmental conditions in much the same way as observed for the lipid/PEG−lipid system. Our investigation showed, furthermore, that the choice of surfactant may influence the type of mixed micelles formed. It is argued that the formation of discoidal rather than threadlike micelles may be rationalized as an effect of increasing bending rigidity. Our detailed theoretical model calculations show that the bending rigidity becomes significantly raised for aggregates formed by an ionic rather than a nonionic surfactant.

  • 40. Kadi, M.
    et al.
    Hansson, P.
    Almgren, M.
    Bergström, Lars Magnus
    Garamus, V. M.
    Mixed micelles of fluorocarbon and hydrocarbon surfactants. A small angle neutron scattering study2004Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 20, nr 10, s. 3933-3939Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mixtures of the partly fluorinated cationic surfactant HFDePC (N-(1, 1,2,2-tetrahydroperfluorodecanyl)pyridinium chloride and deuterated headgroup) with C(16)TAC, hexadecyl-trimethylammonium chloride, have been investigated using small angle neutron scattering with contrast matching. Earlier results from this system suggested that a demixing occurred, into two coexisting populations of micelles, hydrocarbon-rich and fluorocarbon-rich, respectively. The present results could be explained by one type of mixed micelles with an inhomogeneous distribution of fluorinated and hydrogenated surfactants within the micelles although a demixing cannot be definitely excluded.

  • 41.
    Naderi, Ali
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    Claesson, Per Martin
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Bergström, Lars Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Dedinaite, Andra
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    Trapped non-equilibrium states in aqueous solutions of oppositelycharged polyelectrolytes and surfactants: effects of mixing protocoland salt concentration2005Inngår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 253, nr 1-3, s. 83-93Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The very slow equilibration time in oppositely charged systems makes it necessary to control not only the concentration of the species but also the details of the mixing process. This has been demonstrated for processes occurring at interfaces where order of addition effects can be of great importance. In this investigation we set out to study the bulk properties of aqueous mixtures of a highly charged cationic polyelectrolyte mixed with an anionic surfactant with the aim to learn if long-lived non-equilibrium states were formed also in this case, and thus if the details of the mixing procedure would affect the structure of the aggregates formed. For simplicity we chose two mixing protocols, denoted “PTS” and “STP”. In the PTS-method the polyelectrolyte is added to the surfactant solution whereas in the STP-method the surfactant is added into the polyelectrolyte solution. The properties of the mixtures in aqueous solutions, with different NaCl concentrations and as a function of time, were followed by conducting turbidity, electrophoretic mobility and dynamic light scattering measurements. The results demonstrate that the mixing protocol indeed has a great impact on the size of the aggregates initially formed and that this size difference persists for long times. Hence, trapped non-equilibrium states do play an important role also in the bulk solution. We found that in excess surfactant solutions the smaller aggregates formed by the STP-method are more resistant than the larger ones formed by the PTS-method to colloidal instability induced by electrolytes (NaCl). Based on our results we suggest that for producing small and stable polyelectrolyte–surfactant aggregates in systems with excess surfactant, the surfactant should be added last, while the opposite should be applied for systems with excess polyelectrolyte.

  • 42. Persson, C. M.
    et al.
    Jonsson, A. P.
    Bergström, Lars Magnus
    KTH, Tidigare Institutioner                               , Kemi.
    Eriksson, J. C.
    Testing the Gouy-Chapman theory by means of surface tension measurements for SDS-NaCl-H2O mixtures2003Inngår i: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 267, nr 1, s. 151-154Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Surface tension isotherms were measured for sodium dodecyl sulfate (SDS) at different concentrations of added salt (NaCl). The free energy of the surfactant monolayer was assessed by invoking the Gouy-Chapman theory for the charged head groups, the hydrophobic (Tanford) free energy of transfer of the hydrocarbon chain, and the hydrocarbon chain configurational free energy according to Gruen's calculations and finally macroscopic contact terms. In particular, the effect of an increased salt concentration in bulk was examined. Theoretical predictions compare well with the experimental findings, and good agreement was found with respect to both the variation of free energy of the monolayer and the surface pressure behavior. Thus, at least for a liquid-expanded monolayer of SDS, the Gouy-Chapman model yields a satisfactory account of the electrostatic contribution to the thermodynamic properties at different salt concentrations of NaCl.

  • 43.
    Pettersson, Torbjörn
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi.
    Utsel, Simon
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi.
    Carlmark, Anna
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Ytbehandlingsteknik.
    Bergström, Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Malmström, Eva
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Ytbehandlingsteknik.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi.
    Adhesive and adsorption properties of a cationic amphiphilic block copolymer for use as compatibilizer in (bio)-composites2011Inngår i: EUPOC 2011, Biobased Polymers and Related Biomaterials, 2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The awareness of our need for a sustainable society has encouraged the search for renewable, high quality materials that can replace oil-based products. This has stimulated a lot of research where cellulosic fibres are combined with different types of polymer matrices to obtain more environmentally friendly composite materials. However, the compatibility between the different components in a composite, which is of decisive importance for its final properties, is a large problem in many systems today. In this work, the objective was to create a novel type of compatibilizer that can physically adsorb onto fibres to enhance the interaction between fibres and non-polar polymer matrices in fibre-reinforced composites, both by addressing surface energies and by introducing polymer entanglements at the interface. This physical route is much more convenient compared to covalent attachment since it can be performed in water under mild conditions and therefore does not require any use of organic solvents for the attachment of the compatibilizer. To achieve this, an amphiphilic block copolymer with one high molecular weight hydrophobic block (polystyrene, PS) and one cationic block (poly(dimethylamino)ethyl methacrylate, PDMAEMA) was synthesized. Due to the cationic charges, the polymers adsorb to oppositely charged surfaces resulting in a measured contact angle close to that of many non-polar polymer matrices. The adhesion, (measured with atomic force microscopy, AFM, using the colloidal probe technique), of the surface with compatibilizer towards a non-polar PS-probe increased with increasing contact time, most probably due to polymer entanglements between the non-polar blocks at the treated surface and the probe. This demonstrates that the use of this type of novel amphiphilic block copolymer is a promising route to improve the compatibility between charged reinforcing materials such as cellulose-based fibres but also glass-fibres, nanoclay, nanofibrillated cellulose and other charged reinforcing materials, and hydrophobic matrices in composite materials. Limitations when designing new materials due to a lack in compatibility could in this way be addressed in an easy but effective way resulting in more environmentally friendly materials with improved mechanical properties.

  • 44.
    Utsel, Simon
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Carlmark, Anna
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Pettersson, Torbjörn
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Bergström, Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Malmström, Eva E.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Synthesis, adsorption and adhesive properties of a cationic amphiphilic block copolymer for use as compatibilizer in composites2012Inngår i: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 48, nr 7, s. 1195-1204Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, the objective was to synthesize a compatibilizer that can electrostatically adsorb onto cellulose fibers, in fiber-based composites, to enhance the interaction between the fibers and non-polar polymer matrices. This physical route to attach the compatibilizer onto and thereby modify a fiber surface is convenient since it can be performed in water under mild conditions. Polystyrene (PS) was used for the high molecular weight, non-polar, block and poly(dimethylamino)ethyl methacrylate (PDMAEMA) was used as the polar block, which was subsequently quaternized to obtain cationic charges. The block copolymer self-assembles in water into cationic micelles and the adsorption to both silicon oxide surfaces and cellulose model surfaces was studied. The micelles spread out on the surface after heat treatment and contact angle measurements showed that the contact angles against water increased significantly after this treatment. AFM force measurements were performed with a PS probe to study the adhesive properties. The adhesion increased with increasing contact time for the treated surfaces, probably due to entanglements between the polystyrene blocks at the treated surface and the probe. This demonstrates that the use of this type of amphiphilic block copolymer is a promising route to improve the compatibility between charged reinforcing materials, such as cellulose-based fibers/fibrils, and hydrophobic matrices in composite materials.

  • 45.
    Utsel, Simon
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Carlmark, Anna
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Pettersson, Torbjörn
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Bergström, Magnus
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Malmström, Eva
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Synthesis, adsorption and adhesive properties of a cationic amphiphilic block copolymer for use as compatibilizer in composites2011Inngår i: ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY: volume 241, 2011, Vol. 241Konferansepaper (Annet vitenskapelig)
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