title: Poroelastic model for adsorption-induced deformation of biopolymers obtained from molecular simulations.
abstract: Molecular simulation of adsorption of water molecules in nanoporous amorphous biopolymers, e.g., cellulose, reveals nonlinear swelling and nonlinear mechanical response with the increase in fluid content. These nonlinearities result from hydrogen bond breakage by water molecules. Classical poroelastic models, employing porosity and pore pressure as basic variables for describing the "pore fluid," are not adequate for the description of these systems. There is neither a static geometric structure to which porosity can sensibly be assigned nor arrangements of water molecules that are adequately described by giving them a pressure. We employ molar concentration of water and chemical potential to describe the state of the "pore fluid" and stress-strain as mechanical variables. A thermodynamic description is developed using a model energy function having mechanical, fluid, and fluid-mechanical coupling contributions. The parameters in this model energy are fixed by the output of the initial simulation and validated with the results of further simulation. The poroelastic properties, e.g., swelling and mechanical response, are found to be functions both of the molar concentration of water and the stress. The basic fluid-mechanical coupling coefficient, the swelling coefficient, depends on the molar concentration of water and stress and is interpreted in terms of porosity change and solid matrix deformation. The difference between drained and undrained bulk stiffness is explained as is the dependence of these moduli on concentration and stress.
authors.affiliation: Chair of Building Physics, Swiss Federal University of Technology ETH Zurich, Stefano-Franscini-Platz 5, 8093 Zürich, Switzerland.|Laboratory of Multiscale Studies in Building Physics, Swiss Federal Laboratories for Materials Science and Technology Empa, Überlandstrasse 129, 8600 Dübendorf, Switzerland.
authors.forename: Karol
authors.initials: K
authors.lastname: Kulasinski
authors.affiliation: Solid Earth Geophysics Group, Los Alamos National Laboratory, MS D446, Los Alamos, New Mexico 87545, USA.|Department of Physics, University of Nevada, Reno, Nevada 89557, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Guyer
authors.affiliation: Laboratory of Multiscale Studies in Building Physics, Swiss Federal Laboratories for Materials Science and Technology Empa, Überlandstrasse 129, 8600 Dübendorf, Switzerland.
authors.forename: Dominique
authors.initials: D
authors.lastname: Derome
authors.affiliation: Chair of Building Physics, Swiss Federal University of Technology ETH Zurich, Stefano-Franscini-Platz 5, 8093 Zürich, Switzerland.|Laboratory of Multiscale Studies in Building Physics, Swiss Federal Laboratories for Materials Science and Technology Empa, Überlandstrasse 129, 8600 Dübendorf, Switzerland.
authors.forename: Jan
authors.initials: J
authors.lastname: Carmeliet
mesh_terms: D000327:Adsorption; D001704:Biopolymers / Q000737:chemistry*; D002482:Cellulose / Q000737:chemistry; D004548:Elasticity; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D056004:Molecular Dynamics Simulation; D017711:Nonlinear Dynamics; D016062:Porosity; D013314:Stress, Mechanical; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D001704:Biopolymers; D014867:Water; D002482:Cellulose