Browsing by Author "Raghuwanshi, VS"

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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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    Effect of temperature on the conformation and functionality of poly(N-isopropylacrylamide) (PNIPAM)-grafted nanocellulose hydrogels
    (Elsevier, 2023-12-15) Raghuwanshi, VS; Mendoza, DJ; Browne, C; Ayurini, M; Gervinskas, G; Hooper, JF; Mata, JP; Wu, CM; Simon, GP; Garnier, G
    Hypothesis Poly(N-isopropylacrylamide) [PNIPAM]-grafted cellulose nanofibers (CNFs) are new thermo-responsive hydrogels which can be used for a wide range of applications. Currently, there is no clear understanding of the precise mechanism by which CNFs and PNIPAM interact together. Here, we hypothesize that the physical crosslinking of grafted PNIPAM on CNF inhibits the free movement of individual CNF, which increases the gel strength while sustaining its thermo-responsive properties. Experiments The thermo-responsive behaviour of PNIPAM-grafted CNFs (PNIPAM-g-CNFs), synthesized via silver-catalyzed decarboxylative radical polymerization, and PNIPAM-blended CNFs (PNIPAM-b-CNFs) was studied. Small angle neutron scattering (SANS) combined with Ultra-SANS (USANS) revealed the nano to microscale conformation changes of these polymer hybrids as a function of temperature. The effect of temperature on the optical and viscoelastic properties of hydrogels was also investigated. Findings Grafting PNIPAM from CNFs shifted the lower critical solution temperature (LCST) from 32 °C to 36 °C. Below LCST, the PNIPAM chains in PNIPAM-g-CNF sustain an open conformation and poor interaction with CNF, and exhibit water-like behaviour. At and above LCST, the PNIPAM chains change conformation to entangle and aggregate nearby CNFs. Large voids are formed in solution between the aggregated PNIPAM-CNF walls. In comparison, PNIPAM-b-CNF sustains liquid-like behaviour below LCST. At and above LCST, the blended PNIPAM phase separates from CNF to form large aggregates which do not affect CNF network and thus PNIPAM-b-CNF demonstrates low viscosity. Understanding of temperature-dependent conformation of PNIPAM-g-CNFs engineer thermo-responsive hydrogels for biomedical and functional applications. © 2023 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license.
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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
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    A study of the interaction between polyelectrolytes and biomolecules at the solid/solution interface with neutron specular reflectivity
    (International Conference on Neutron Scattering, 2017-07-12) Garvey, CJ; Raghuwanshi, VS; Su, J; Raverty, W; Holt, SA; Holden, PJ; Garnier, G
    Cellulose fibres may be formed into a low cost substrate, paper, for the adsorption of biomolecules to form the basis of cheap robust diagnostic tests. Important issues for the development of this technology are the retention of the biomolecules and maintaining the activity of the absorbed biomolecule. Typically the large internal surface is rough and there are limited experimental techniques to directly examine the structure of the adsorbed layer. In this work we describe our progress in using neutron and x-ray reflectivity to study the interaction between the cellulose surface and various adsorbed biomolecules with the aim to produce a model system to provide fundamental understanding for the production of robust paper based sensors. We have produced flat cellulose films from biodeuterated cellulose of varying degrees of non-exchangeable deuteration using bacterial cellulose produced with deuterated carbon sources. The films are amorphous with the fully hydrated films exhibiting 100% exchangeability of hydroxyl cellulose groups. The enhanced contrast, with respect to protein in particular, will allow visualisation of this class of molecules on the surface. The films are suitable for the visualisation of the diffuseness of a layer of cationic polyelectrolyte adsorbed to a cellulose surface. Giving, in principle,control on the charge sign and density of the cellulose surface for adsorption of biomolecules.