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Trapped non-equilibrium states in aqueous solutions of oppositelycharged polyelectrolytes and surfactants: effects of mixing protocoland salt concentration
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.ORCID iD: 0000-0002-2288-819X
2005 (English)In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, Vol. 253, no 1-3, 83-93 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2005. Vol. 253, no 1-3, 83-93 p.
Keyword [en]
Polyelectrolyte, Surfactant, Polyelectrolyte–surfactant complex; Polyelectrolyte–surfactant aggregate; Polyelectrolyte–surfactant association; Turbidity, Electrophoretic mobility; Dynamic light scattering; Colloidal stability; Non-equilibrium state; Trapped state; Polydispersity
National Category
Natural Sciences Chemical Sciences
URN: urn:nbn:se:kth:diva-58941DOI: 10.1016/j.colsurfa.2004.10.123ISI: 000226934900010ScopusID: 2-s2.0-12344329184OAI: diva2:474441
NOTICE: this is the author’s version of a work that was accepted for publication in Colloids and Surfaces A. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in PUBLICATION, VOL 253, ISSUE1-3, 15 December 2004, DOI: 10.1016/j.colsurfa.2004.10.123. QC 20120118Available from: 2012-01-18 Created: 2012-01-09 Last updated: 2012-03-21Bibliographically approved
In thesis
1. Polyelectrolytes: Bottle-Brush Architectures and Association with Surfactants
Open this publication in new window or tab >>Polyelectrolytes: Bottle-Brush Architectures and Association with Surfactants
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis has the dual purpose of raising awareness of the importance of the mixing protocol on the end products of polyelectrolyte-oppositely charged surfactant systems, and to contribute to a better understanding of the properties of bottle-brush polyelectrolytes when adsorbed onto interfaces.

In the first part of this thesis work, the effects of the mixing protocol and the mixing procedure on formed polyelectrolyte-oppositely charged surfactant aggregates were investigated. It was shown that the initial properties of the aggregates were highly dependent on the mixing parameters, and that the difference between the resulting aggregates persisted for long periods of time.

The second part of the studies was devoted to the surface properties of a series of bottle-brush polyelectrolytes made of charged segments and segments bearing poly(ethylene oxide) side chains; particular attention was paid to the effect of side chain to charge density ratio of the polyelectrolytes. It was shown that the adsorbed mass of the polyelectrolytes, and the corresponding number of poly(ethylene oxide) bearing segments at the interface, went through a maximum as the charge density of the polyelectrolyte was increased. Also, it was found that bottle-brush polyelectrolyte layers were desorbed quite easily when subjected to salt solutions. This observation was rationalized by the unfavourable excluded volume interactions between the side chains and the entropic penalty of confining them at an interface, which weaken the strength of the binding of the polyelectrolytes to the interface. However, it was shown that the same side chains effectively protect the adsorbed layer against desorption when the layer is exposed to solutions containing an oppositely charged surfactant. Investigation of the lubrication properties of the bottle-brush polyelectrolytes in an asymmetric (mica-silica) system also related the observed favourable frictional properties to the protective nature of the side chains. The decisive factor for achieving very low coefficients of friction was found to be the concentration of the side chains in the gap between the surfaces. Interestingly, it was shown that a brush-like conformation of the bottle-brush polyelectrolyte at the interface has little effect on achieving favourable lubrication properties. However, a brush-like conformation is vital for the resilience of the adsorbed layer against the competitive adsorption of species with a higher surface affinity.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. 39 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2008:18
Polyelectrolyte, Surfactant, Bottle-Brush Polyelectrolyte, Comb Polyelectrolyte, Non-Equilibrium State, Polymer Architecture, Adsorption, Desorption, Association, Excluded Volume, Light Scattering, SFA, AFM, QCM-D, Turbidimeter, Mica, Silica, Surface Forces
National Category
Physical Chemistry
urn:nbn:se:kth:diva-4683 (URN)978-91-7178-903-7 (ISBN)
Public defence
2008-04-18, F3, Lindstedsvägen 28 100 44, Stockholm, 10:00
QC 20100830Available from: 2008-03-27 Created: 2008-03-27 Last updated: 2012-01-20Bibliographically approved

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