Department of Chemical Engineering

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Subject: search.filters.subject.Nanocellulose

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    Ion Diffusion through Nanocellulose Membranes: Molecular Dynamics Study
    (ACS, 2021-12) Garg, Mohit
    One of the most promising applications of nanocellulose is for membranes for energy storage devices including supercapacitors, batteries, and fuel cells. Several recent studies reported the fabrication of cellulose-based membranes where ionic conductivity was confined to channels. So far, theoretical understanding of the effect of the nanoconfinement and surface charged groups on the diffusion coefficient of ions in cellulose nanochannels is missing. In the present study, we perform atomistic molecular dynamics simulations to provide this theoretical understanding and unravel mechanisms affecting the ionic diffusion in nanochannels. We demonstrate that the diffusion coefficient of ions in cellulose nanochannels is reduced in comparison to its bulk value. The change of the diffusion coefficient depends on the density of charged surface groups in nanochannels and the channel height, and it is primarily caused by the Coulomb interaction between the ions and the surface. We believe that our results reveal an important structure/property relationship in cellulose nanochannels, and they show that accounting for the dependence of the diffusion coefficient on the charge of the surface groups and channel height can be important for the Nernst–Plank–Poisson modeling of the ion conductivity in nanomembranes as well as for accurate fitting the experimental data to extract the material parameters.
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    Humidity-Dependent Thermal Boundary Conductance Controls Heat Transport of Super-Insulating Nanofibrillar Foams
    (Elsevier, 2021-01) Garg, Mohit
    Cellulose nanomaterial (CNM)-based foams and aerogels with thermal conductivities substantially below the value for air attract significant interest as super-insulating materials in energy-efficient green buildings. However, the moisture dependence of the thermal conductivity of hygroscopic CNM-based materials is poorly understood, and the importance of phonon scattering in nanofibrillar foams remains unexplored. Here, we show that the thermal conductivity perpendicular to the aligned nanofibrils in super-insulating ice-templated nanocellulose foams is lower for thinner fibrils and depends strongly on relative humidity (RH), with the lowest thermal conductivity (14 mW m−1 K−1) attained at 35% RH. Molecular simulations show that the thermal boundary conductance is reduced by the moisture-uptake-controlled increase of the fibril-fibril separation distance and increased by the replacement of air with water in the foam walls. Controlling the heat transport of hygroscopic super-insulating nanofibrillar foams by moisture uptake and release is of potential interest in packaging and building applications.