Aurélia Charlot

Modification of polysaccharides through controlled/living radical polymerization grafting - Towards the generation of high performance hybrids

This review covers the literature concerning the modification of polysaccharides through controlled radical polymerizations (NMP, ATRP and RAFT). The different routes to well-defined polysaccharide-based macromolecules (block and graft copolymers) and graft-functionalized polysaccharide surfaces as well as the applications of these polysaccharide-based hybrids are extensively discussed.

Green nondegrading approach to alkyne-functionalized cellulose fibers and biohybrids thereof: synthesis and mapping of the derivatization.

Alkyne-functionalized cellulose fibers have been generated through etherification under basic water or hydroalcoholic conditions (NaOH/H(2)O/isopropanol). For a given NaOH content, the medium of reaction and, more particularly, the water/IPA ratio, were shown to be of crucial importance to derivatize the fibers without altering their integrity and their crystalline nature. It was shown that the degree of substitution (DS) of the fibers increases concomitantly with isopropanol weight ratio and that, contrary to water or water-rich conditions, derivatization of fibers under isopropanol-rich conditions induces an alteration of the fibers. Optimization of etherification conditions in aqueous media afforded functionalized cellulose materials with DS up to 0.20. Raman confocal microscopy on derivatized fibers cross sections stressed that alkyne moieties are incorporated all over the fibers. The resulting fibers were postfunctionalized by molecular probes and macromolecules in aqueous or water-rich conditions. The effectiveness of the grafting was strongly impacted by the nature of the coupling agents.

Layer by Layer H-Bonded Assembly of P4VP with Various Hydroxylated PPFS: Impact of the Donor Strength on Growth Mechanism and Surface Features

Hydrogen bond mediated films made by step by step deposition of poly(4-vinylpyridine) (P4VP) and hydroxylated poly(2,3,4,5,6-pentafluorostyrene) (PPFS) copolymers prepared by thiol para-fluoro coupling, bearing either one (PPFSME) or two (PPFSMPD) hydrogenated hydroxyl groups or a (poly)fluorinated hydroxyl (PPFSOH), respectively, were successfully constructed. The influence of the structural parameters, such as the hydroxyl environment (which dictates the H-bond strength) was in-depth investigated in terms of their impact on (i) growth mechanism, (ii) internal organization, and (iii) surface features. The use of the weaker H-bond donor partner (PPFSME) leads to low quality films composed of irregularly distributed aggregates. While [PPFSMPD/P4VP] multilayer films are comparatively thick and composed of stratified layers with smooth topology, the use of PPFSOH with P4VP yields thin films made of mixed and interpenetrated polymer layers. Playing on the interaction strength appears as a powerful tool to elaborate tailored multilayer films with molecularly tunable properties.

Microcrystalline cellulose as reinforcing agent in silicone elastomers

Cellulose is commonly used as filler for the reinforcement of polymer materials but data in the case of silicones remain rare. In this work we report the modification of microcrystalline cellulose (MCC) fibers from cotton linters by propargyl bromide, in aqueous medium without alteration of the crystalline domains. The analysis evidenced the efficient grafting of alkyne functions at the surface of the fibers, the DS being 0.5. The resulting MCC-Alkyne fibers were introduced within a bi-component reactive silicone formulation (up to 20wt%), allowing the formation of network through hydrosilylation reaction in which MCC-Alkyne played the role of a reactive fillers. Comparison between the properties of composites prepared with unmodified MCC and MCC-Alkyne highlighted a densification of the network and an enhancement of mechanical and thermal properties when coupling reactions occurred. Mechanical properties of silicone elastomers were better if the load of MCC-Alkyne remains low.

Dual guar/ionic liquid gels and biohybrid material thereof: rheological investigation.

Polysaccharide-based ion gels were prepared by mixing biosourced guar gums with imidazolium ionic liquid (IL) molecules that act as crosslinking agents. The in-depth investigation of the rheological properties of the guar/IL solutions emphasized that the shear viscoelastic properties can be finely tuned by IL chemical structure, concentration and molecular weight of guar chains as well as by temperature changes. Under suited conditions, highly elastic physical ion gels were formed as a result of multiple guar/IL, guar/guar and IL/IL interactions. Such synergistic associations were usefully exploited to elaborate films dually composed of guar chains and entrapped IL molecules. Their thermomechanical properties, which revealed a solid-state behavior, were closely controlled by the structural parameters of the constituents. This straightforward approach, which requires no chemical derivatization step, provides a facile way to design physical gels with a large applicative potential.

Homogeneously and gradually anchored self-assembled monolayer by tunable vapor phase-assisted silanization

A versatile and straightforward grafting approach in the vapor phase was developed in view of preparing alkyl self-assembled monolayers uniformly or gradually anchored onto silica surfaces, as demonstrated by wettability and XPS measurements. The understanding of the mechanism which dictates the grafting in the vapor phase was investigated through changing the experimental parameters. The control of the propagating front diffusion consisting of silane vapor afforded a concentration gradient, leading to a gradual grafting with features such as hydrophobicity steepness and spatial amplitude which can be tuned by changing the time and/or temperature of exposure. This results in changes to the concentration and diffusion of the vaporized silane molecules as well as changing the silane–substrate’s interfacial chemical reactivity. Such single-component gradient surfaces were utilized as molecular (nano)templates to generate a heterogeneous two-component gradient by simply performing a backfilling with fluorine or amine-functionalized silane derivatives.

Biohybrid cellulose fibers: Toward paper materials with wet strength properties

Herein, we report on the preparation of novel cellulose-PEG biohybrid papers with wet strength properties. The biohybrid paper sheets are obtained using a two-step procedure where ω- or α, ω-azide functionalized PEG chains are anchored onto alkyne-functionalized wood fibers through CuAAC ligation in mild and aqueous conditions. The incorporation of the PEG grafts mostly occurs at the periphery of the cellulose fibers and degrees of substitution up to 0.028 are obtained. The presence of PEG grafts significantly increases the tensile, burst and tear strength properties in the wet state, the reinforcement being more pronounced for fibers grafted with α,ω-azide PEG. This reinforcement is consistent with a relatively sparse hetero-crosslink reaction creating inter-fiber covalent bonds and forming a cellulose network within the cell wall.