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  • 1.
    Liu, Yingxin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, Sweden.
    Nanocellulose-based materials: from colloidal assembly to functional films2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The assembly of nature-based nanomaterials into complex architectures is both a design principle of biological composites, e.g., wood and nacre with outstanding properties and a promising route for developing functional macroscopic materials. This thesis aims to investigate and understand the colloidal and self-assembly behaviour of nanocellulose in aqueous dispersions. Moreover, composite films of nanocellulose and nanoclay/lignin with diverse functionalities, e.g., mechanical and optical properties, are fabricated by tailoring the electrostatic interactions of these building blocks.

    The evaporation induced assembly of sulfonated cellulose nanocrystal (CNC) has been followed in either an aqueous droplet on substrates or a levitated droplet by real-time small angle X-ray scattering. The evolution of structural features, e.g., an isotropic phase, biphasic phase, fully liquid crystalline and contracted helical structures of drying CNC dispersions were related to the power-law scaling of the particle separation distance (d) with concentrations (c, from 1 vol% to 38 vol%). Below 2 vol%, CNC dispersions consolidated isotropically with a scaling of d c-1/3, while the fully cholesteric liquid crystalline phase showed a unidimensional contraction of the nematic structure (d c-1) with increasing concentrations. Competition between gelation and the ordered assembly of CNC was quantitatively evaluated in nanoscale for the first time, which was reflected by a scaling of d c-2/3.

    The rheology of composite dispersions of carboxylated cellulose nanofibril (CNF) and nanoclay was investigated, which was influenced by the surface charge of CNF, the morphology of nanoclays and interactions between CNF and clay particles. Optically transparent films of synthetic aminoclay (50 wt%) and CNF were fabricated, of which tensile strength and strain to failure (205 MPa and 7.5%) were significantly higher than those of nacre and other nacre-mimicking nanocellulose-based materials, e.g., montmorillonite-CNF films, due to the formation of ionic bonding between the cationic clay and anionic CNF.

    Lignin nanoparticles were testified to enhance the colloidal stability and dispersity of carboxylated CNF in dispersions, and showed a remarkable strengthening and stiffening effect on the matrix of CNF. The mechanical properties of lignin-CNF films were superior to previously reported polymer/nanoparticle-CNF composites, such as polyvinyl alcohol-CNF films and even reduced graphene oxide-CNF films.

  • 2.
    Liu, Yingxin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, Sweden.
    Strong and Flexible Nanocomposites of Carboxylated Cellulose Nanofibril Dispersed by Industrial Lignin2018In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 6, no 4, p. 5524-5532Article in journal (Refereed)
    Abstract [en]

    We demonstrated that industrial lignin can be facilely processed with carboxylated cellulose nanofibril (CNF) to obtain strong, flexible, and transparent nanocomposites via film casting of dispersions. The tensile strength and strain to failure of lignin–CNF nanocomposites (245 MPa and 15%, respectively at 7.7 wt % of lignin) are superior to previously reported polymer/nanoparticle–CNF composites with polymer contents below 50 wt %, such as poly(vinyl alcohol)–CNF films and even reduced graphene oxide–CNF films. The excellent mechanical properties of lignin–CNF nanocomposite films are related to the lignin-enhanced colloidal stability and dispersity of CNF in aqueous dispersions supported by measurements of rheology and dynamic light scattering, which accordingly suppresses the excess fibril aggregates during film formation. Moreover, lignin in the nanocomposites benefits an efficient functionalization of gold/iron oxide nanoparticles on the surface of nanocomposites. This study illustrates the great potential of industrial lignin in developing nanocellulose-based materials with advanced properties and functionalities.

  • 3.
    Liu, Yingxin
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). KTH, Sweden.
    Agthe, Michael
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Salajková, Michaela
    Gordeyeva, Korneliya
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Guccini, Valentina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). KTH, Sweden.
    Fall, Andreas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Salazar-Alvarez, Germán
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). KTH, Sweden.
    Schütz, Christina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). KTH, Sweden.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Assembly of cellulose nanocrystals in a levitating drop probed by time-resolved small angle X-ray scattering2018In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 10, no 38, p. 18113-18118Article in journal (Refereed)
    Abstract [en]

    Assembly of bio-based nano-sized particles into complex architectures and morphologies is an area of fundamental interest and technical importance. We have investigated the assembly of sulfonated cellulose nanocrystals (CNC) dispersed in a shrinking levitating aqueous drop using time-resolved small angle X-ray scattering (SAXS). Analysis of the scaling of the particle separation distance (d) with particle concentration (c) was used to follow the transition of CNC dispersions from an isotropic state at 1-2 vol% to a compressed nematic state at particle concentrations above 30 vol%. Comparison with SAXS measurements on CNC dispersions at near equilibrium conditions shows that evaporation-induced assembly of CNC in large levitating drops is comparable to bulk systems. Colloidal states with d vs. c scalings intermediate between isotropic dispersions and unidirectional compression of the nematic structure could be related to the biphasic region and gelation of CNC. Nanoscale structural information of CNC assembly up to very high particle concentrations can help to fabricate nanocellulose-based materials by evaporative methods.

  • 4.
    Liu, Yingxin
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, Sweden.
    Gordeyeva, Korneliya
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Steady-shear and viscoelastic properties of cellulose nanofibril-nanoclay dispersions2017In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 24, no 4, p. 1815-1824Article in journal (Refereed)
    Abstract [en]

    We have investigated the steady-shear and viscoelastic properties of composite dispersions of cellulose nanofibrils (CNFs) with medium or high charge density and two different nanoclays, viz. rodlike sepiolite or plate-like bentonite. Aqueous dispersions of CNFs with medium charge density displayed significantly lower steady-state viscosity and storage modulus but higher gelation threshold compared with CNFs with high charge density. Dynamic light scattering (DLS) results showed that the apparent hydrodynamic radius of bentonite particles increased when CNFs were added, implying that CNFs adsorbed onto the amphoteric edges of the plate-like bentonite particles. The sepiolite network in CNF-sepiolite dispersions was relatively unaffected by addition of small amounts of CNFs, and DLS showed that the hydrodynamic radius of sepiolite did not change when CNFs were added. Addition of CNFs at concentrations above the gelation threshold resulted in drastic decrease of the steady-shear viscosity of the sepiolite dispersion, suggesting that the sepiolite network disintegrates and the rod-like clay particles are aligned also at low shear rate. The relative change in the rheological properties of the clay-based dispersions was always greater on addition of CNFs with high compared with medium charge density. This study provides insight into how the rheology of CNF-nanoclay dispersions depends on both the nanoclay morphology and the interactions between the nanoclay and nanocellulose particles, being of relevance to processing of nanocellulose-clay composites.

  • 5.
    Liu, Yingxin
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, KTH, Sweden.
    Schütz, Christina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, KTH, Sweden.
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, KTH, Sweden.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Assembly, Gelation, and Helicoidal Consolidation of Nanocellulose Dispersions2019In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 35, no 10, p. 3600-3606Article in journal (Refereed)
    Abstract [en]

    The ability to probe the assembly, gelation, and helicoidal consolidation of cellulose nanocrystal (CNC) dispersions at high concentrations can provide unique insight into the assembly and can assist optimized manufacturing of CNC-based photonic and structural materials. In this Feature Article, we review and discuss the concentration dependence of the structural features, characterized by the particle separation distance and the helical pitch, at CNC concentrations (c) that range from the isotropic state, over the biphasic range, to the fully liquid crystalline state. The structure evolution of CNC dispersions probed by time resolved small-angle X-ray scattering during evaporation-induced assembly highlighted the importance of gelation and consolidation at high concentrations. We briefly discuss how the homogeneity of helicoidal nanostructures in dry CNC films can be improved and present an outlook for future work.

  • 6.
    Liu, Yingxin
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, Sweden.
    Stoeckel, Daniela
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gordeyeva, Korneliya
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Agthe, Michael
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Schütz, Christina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Fall, Andreas B.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nanoscale Assembly of Cellulose Nanocrystals during Drying and Redispersion2018In: ACS Macro Letters, E-ISSN 2161-1653, Vol. 7, no 2, p. 172-177Article in journal (Refereed)
    Abstract [en]

    We have followed the structural evolution during evaporation-induced self-assembly of sulfonated cellulose nanocrystal (CNC) in the presence of H+ and Li+ counterions by small-angle X-ray scattering. Drying of CNC-H dispersions results in ordered films that could not be readily redispersed, while the CNC-Li films were disordered and prone to reswelling and redispersion. The scaling of the separation distance (d) between CNC particles and the particle concentration (c) shows that the CNC-H dispersions display a unidimensional contraction of the nematic structure (d alpha c(-1)) during drying, while the CNC-Li dispersions consolidate isotropically (d alpha c(-1/3)), which is characteristic for hydrogels with no preferential orientation. Temporal evolution of the structure factor and complementary dynamic light-scattering measurements show that CNC-Li is more aggregated than CNC-H during evaporation-induced assembly. Insights on the structural evolution during CNC assembly and redispersion can promote development of novel and optimized processing routes of nanocellulose-based materials.

  • 7.
    Liu, Yingxin
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, Sweden.
    Yu, Shu-Hong
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, Sweden.
    Transparent and Flexible Nacre‐Like Hybrid Films of Aminoclays and Carboxylated Cellulose Nanofibrils2018In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 28, no 27, article id 1703277Article in journal (Refereed)
    Abstract [en]

    Nacre and other biological composites are important inspirations for the design and fabrication of multifunctional composite materials. Transparent, strong, and flexible hybrid films of aminoclays (AC) and carboxylated cellulose nanofibrils (CNF) with a nacre‐like microstructure at AC contents up to 60 wt% are prepared. The high transmittance of visible light is attributed to the high homogeneity of the hybrid films and to the relatively small refractive index contrast between the CNF‐based matrix and synthetic AC. The strength and strain to failure of the hybrids are significantly higher than biogenic nacre and other nacre‐mimicking nanocellulose‐based materials, e.g., montmorillonite‐CNF and graphene oxide‐CNF composite films. The excellent mechanical properties are related to the ionic bonds between the negatively charged carboxylic groups on the CNF and the positively charged amine groups on the AC nanoparticles. This work illustrates the significance of tailoring the interactions between small clay particles and biopolymers in multifunctional materials with potential applications as printable barrier coatings and substrates for optoelectronics.

1 - 7 of 7
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