Browsing by Author "Garnier, GFG"

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    Cellulose dissolution in ionic liquid: ion binding revealed by neutron scattering
    (ACS Publications, 2018-09-20) Raghuwanshi, VS; Cohen, Y; Garnier, GFG; Garvey, CJ; Russell, RA; Darwish, TA; Garnier, G
    Dissolution of cellulose in 1-ethyl-3-methylimidazolium acetate (EMIMAc) ionic liquid (IL) was investigated by small-angle neutron scattering (SANS) with contrast variation. Cellulose and EMIMAc of different deuteration levels provide sufficient contrast in revealing the cellulose dissolution processes. Two experiments were performed: hydrogenated microcrystalline cellulose (MCC) was dissolved in deuterated IL (IL-D14), and deuterated bacterial cellulose (DBC) was dissolved in hydrogenated IL (IL-H14). Contrary to the expectation of high contrast between MCC and IL-D14, a dramatic reduction of the measured intensity (scattering cross section) was observed, about 1/3 of the value predicted based on the scattering length density (SLD) difference. This is attributed to the tight binding of acetate ions to the cellulose chains, which reduces the SLD difference. Measurements using small-angle X-ray scattering (SAXS) corroborate this effect by indicating increased contrast due to ion adsorption resulting in enhanced SLD difference. The experiments performed with DBC dissolution in IL-H14 suggest the presence of fractal aggregates of the dissolved cellulose, indicating lower solubility compared to the MCC. Contrast variation SANS measurements highlight tight ion binding of at least one acetate ion per anhydroglucose unit (AGU). EMIMAc is a successful cellulose solvent, as in addition to disrupting intermolecular hydrogen bonding, it imparts effective charge to the cellulose chains hindering their agglomeration in solution. © 2018 American Chemical Society
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    Modulating the isotopic hydrogen-deuterium exchange in functionalized nanocellulose to optimize SANS contrast
    (Elsevier, 2024-12) Raghuwanshi, VS; Mendoza, DJ; Mata, JP; Garnier, GFG
    Contrast matching by isotopic exchange in cellulose allows visualizing functional groups, biomolecules, polymers and nanoparticles embedded in cellulosic composites. This isotopic exchange varies the scattering length density of cellulose to match its contrast with the background network. Here, contrast matching of microcrystalline-cellulose (MCC) and the functionalized nanocellulose-fiber (CNF) and cellulose nanocrystals (CNC) are elucidated by small angle neutron scattering (SANS). Results show no isotopic exchange occurs for the CNF surface functionalized with carboxyl nor for the CNC-High with a high sulfate groups concentration. Both CNC-Low, with low sulfate groups, and MCC exchange 1H with 1D in D2O. This is due to the high exchange probability of the labile C6 position primary -OH group. The structure of thermo-responsive poly-N-isopropylacrylamide (PNIPAM) chains grafted onto CNF (PNIPAM-grafted-CNF) was extracted by CNF contrast matching near the lower critical solution temperature. Contrast matching eradicates the CNF scattering to retain only the scattering from the grafted-PNIPAM chains. The coil to globule thermo-transition of PNIPAM was revealed by the power law variation from q−1.3 to q−4 in SANS. Isotopic exchange in functionalized cellulosic materials reveals the nano- and micro-scale structure of its individual components. This improved visualization by contrast matching can be extended to carbohydrate polymers to engineer biopharmaceutical and food applications. © 2024 The Authors. Published by Elsevier Ltd. - Open Access CC BY 4.0