Dehydration and Rehydration of Polymeric Porous Media Studied by Molecular Dynamics Modeling and Simulations

Abstract

The dehydration and rehydration phenomena of amylose-based polymeric porous media have been modeled and investigated using molecular dynamics modeling and simulations. As dehydration lowers the water level continuously, surface tension coupled with strong water-polymer interactions exert downward stresses on the polymer chains and the pore structures and eventually cause them to result in reduced pore structures due to lack of sufficient steric support resulting from low polymer chain densities. Dehydration may also cause an exterior solvent phase to develop when the pore structures are formed by sufficiently flexible polymers and sufficiently low polymer densities. Strong water-polymer interactions also make the magnitude of the energy requirement for dehydrating polymeric porous media not only substantially higher than pure water vaporization but the strength of the water-polymer interactions also increases as dehydration-induced pore structural reduction advances to greater extents and the pore sizes become smaller. Furthermore, it causes the interaction energetics of the water molecules in the porous media to be highly nonuniform in the three spatial dimensions before and during dehydration. These results indicate that a single thermodynamic parameter like water activity determined from bulk experimental data is inadequate to represent the diverse energetic states of water in polymeric porous media and to capture the actual mechanisms underlying various phenomena and processes that are occurring in such media. Rehydration is found to expand slightly the dehydration-induced reduced structures of the porous media formed by flexible polymer chains and sufficiently low chain densities (low mutual steric support). The stability of the dehydrated polymeric porous media is provided mainly by the water molecules remaining in the pore structures and whose strong water-polymer interactions "bind" the polymer chains together. Thus, the results of this work indicate that the behavior of the polymeric porous structure during rehydration depends on the dynamic evolution and final state of the dehydrated porous structure. The approach presented here could form a basis for the systematic evaluation of porous polymeric media and their stability from the extent of solvent-polymer, solvent-solvent, and polymer-polymer interactions during wetting, dewetting, and rewetting.

Department(s)

Chemical and Biochemical Engineering

Keywords and Phrases

Chains; Dehydration; Molecular Dynamics; Molecules; Pore Size; Pore Structure; Porosity; Porous Materials; Solvents; Water Levels; Energy Requirements; Flexible Polymer Chains; Molecular Dynamics Modeling; Polymer Interactions; Polymer-Polymer Interaction; Structural Reduction; Systematic Evaluation; Thermodynamic Parameter; Polymers

International Standard Serial Number (ISSN)

0888-5885

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2015 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Nov 2015

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