Ionogel based on biopolymer-silica interpenetrated networks: dynamics of confined ionic liquid with lithium salt.

Obtaining solid-state electrolytes with good electrochemical performances remains challenging. Ionogels, i.e. solid host networks confining an ionic liquid, are promising as they keep the macroscopic properties of the liquid. However, confinement of an ionic liquid can imply important changes in its molecular dynamics, depending on the route of synthesis and on the confining network. We studied this effect on an imidazolium based ionic liquid with its lithium salt confined in a hybrid biopolymer-silica matrix. Dynamics of bulk and confined solution was probed by quasi-elastic neutron scattering (QENS) which revealed a weakly slowed dynamics of imidazolium-based ionic liquid inside the polymer-silica host network.

Discotic columnar liquid crystal studied in the bulk and nanoconfined states by molecular dynamics simulation.

A prototypical Gay Berne discotic liquid crystal was studied by means of molecular dynamics simulations both in the bulk state and under confinement in a nanoporous channel. The phase behavior of the confined system strongly differs from its bulk counterpart: the bulk isotropic-to-columnar transition is replaced by a continuous ordering from a paranematic to a columnar phase. Moreover, a new transition is observed at a lower temperature in the confined state, which corresponds to a reorganization of the intercolumnar order. It reflects the competing effects of pore surface interaction and genuine hexagonal packing of the columns. The translational molecular dynamics in the different phases has been thoroughly studied and discussed in terms of collective relaxation modes, non-Gaussian behavior, and hopping processes.

Thermotropic orientational order of discotic liquid crystals in nanochannels: an optical polarimetry study and a Landau-de Gennes analysis.

Optical polarimetry measurements of the orientational order of a discotic liquid crystal based on a pyrene derivative confined in parallelly aligned nanochannels of monolithic, mesoporous alumina, silica, and silicon as a function of temperature, channel radius (3-22 nm) and surface chemistry reveal a competition of radial and axial columnar orders. The evolution of the orientational order parameter of the confined systems is continuous, in contrast to the discontinuous transition in the bulk. For channel radii larger than 10 nm we suggest several, alternative defect structures, which are compatible both with the optical experiments on the collective molecular orientation presented here and with a translational, radial columnar order reported in previous diffraction studies. For smaller channel radii our observations can semi-quantitatively be described by a Landau-de Gennes model with a nematic shell of radially ordered columns (affected by elastic splay deformations) that coexists with an orientationally disordered, isotropic core. For these structures, the cylindrical phase boundaries are predicted to move from the channel walls to the channel centres upon cooling, and vice-versa upon heating, in accord with the pronounced cooling/heating hystereses observed and the scaling behavior of the transition temperatures with the channel diameter. The absence of experimental hints of a paranematic state is consistent with a biquadratic coupling of the splay deformations to the order parameter.

Xyloglucan-cellulose nanocrystal multilayered films: effect of film architecture on enzymatic hydrolysis.

Understanding the hydrolysis process of lignocellulosic substrates remains a challenge in the biotechnology field. We aimed here at investigating the effect of substrate architecture on the enzymatic degradation process using two different multilayered model films composed of cellulose nanocrystals (CNCs) and xyloglucan (XG) chains. They were built by a spin-assisted layer-by-layer (LbL) approach and consisted either of (i) an alternation of CNC and XG layers or of (ii) layers of mixed (CNC/XG) complexes alternated with polycation layers. Neutron reflectivity (NR) was used to determine the architecture and composition of these films and to characterize their swelling in aqueous solution. The films displayed different [XG]/[CNC] ratios and swelling behavior. Enzymatic degradation of films was then performed and investigated by quartz crystal microbalance with dissipation monitoring (QCM-D). We demonstrated that some architectural features of the substrate, such as polysaccharide accessibility, porosity, and cross-links, influenced the enzymatic degradation.

Coloured semi-reflective thin films for biomass-hydrolyzing enzyme detection.

A new enzymatic activity detection assay based on colour change of the semi-reflective films is presented. The method is based on the preparation of multilayered thin films of controlled thickness obtained by sequential deposition of cellulose nanocrystals and xyloglucan. The hydrolysis of the films leads to a decrease in layer thickness that enables to detect enzyme activity, to the naked eye, from the resulting colour changes in a span of few minutes. The method allows direct, fast, highly sensitive, and easy-to-use characterization of enzymatic activities.

Elaboration of spin-coated cellulose-xyloglucan multilayered thin films.

In the context of developing a biomimetic model of the primary cell wall, our aim was to produce multilayered thin films composed of cellulose nanocrystals (CN) and xyloglucan (XG). We investigated the effect of XG concentrations ranging from 0.5 g/L to 10 g/L. The choice of concentration was based on rheological investigation of the XG solutions which indicated that the two lower concentrations (0.5 and 1 g/L) correspond to a semidilute regime where the polymer chains are not entangled, whereas they are entangled at the highest concentrations (5 and 10 g/L). Several processes of film preparation were tested (dipping or spin-coating, with or without a rinsing step). The film growth profiles obtained for different XG concentrations by mechanical profilometry showed that spin-coating without rinsing was the most efficient process. Results showed that at high XG concentrations (XG = 5 g/L and XG = 10 g/L) plateau values were reached after the formation of 3 or 4 bilayers, whereas growth of the multilayer structure was linear at the lower XG concentrations (XG = 0.5 g/L and XG = 1 g/L). The thickness of one CN/XG bilayer corresponded to a single layer of CN covered by a thin XG layer, despite the absence of a rinsing step between successive coatings. The importance of the XG concentration was confirmed by determining by neutron reflectivity the film architecture obtained from four XG solutions after eight successive paired coatings. The results are discussed in relation to the role of XG in the plant cell wall.

Improved colloidal stability of bacterial cellulose nanocrystal suspensions for the elaboration of spin-coated cellulose-based model surfaces.

Well-dispersed suspensions are a prerequisite when preparing smooth model surfaces based on neutral bacterial cellulose nanocrystals (BCNs). However, neutral nanocrystal suspensions present pronounced particle aggregation. Carboxymethyl cellulose (CMC) or xyloglucan (XG) was therefore added to aggregated BCN suspensions. Turbidity measurements, polysaccharide content, and transmission electron microscopy (TEM) analysis revealed that aggregation of BCNs in CMC/BCN and XG/BCN suspensions is dependent on the concentration of CMC and XG in the suspensions. CMC enhances BCN dispersion above the concentration ratio of 0.05. In the case of XG, a better colloidal stability is observed above the concentration ratio of 0.5. Atomic force microscopy (AFM) investigations demonstrated that cellulose-based model surfaces, spin-coated from CMC/BCN or XG/BCN solutions, exhibited more uniform topography and less roughness than the reference BCN model surface.

Elaboration of extensin-pectin thin film model of primary plant cell wall.

With the aim of mimicking the plant cell wall, a layer by layer approach was used to build a thin film consisting of successive adsorption of pectin and extensin. Elaboration of the thin film was monitored by surface plasmon resonance, quartz crystal microbalance, and ellipsometry. All data indicate that formation of the film was successful and that growth occurred according to a nonuniform growth. It is likely that diffusion of the polymers occurred within the multilayer structure and that the final structure is not constituted by layered individual pectin and extensin films. Polymer rearrangements were also supported by the atomic force microscopy images that show a smoother surface after extensin adsorption than after pectin deposition.