Title

Molecular Dynamics Modeling and Simulation Studies of the Effects of Additive Solutes on the Dehydration and Rehydration of Polymeric Porous Media

Abstract

An amylose-based polymeric porous material with an additive solute, potassium sorbate, has been constructed and studied by molecular dynamics modeling and simulations. It was found that the strong interactions of water molecules with the polymer and additive molecules stabilize the porous structure of the polymeric material and require the dehydration energy to be greater than that involved in pure water vaporization. They also cause the water interaction energetics to be highly nonuniform in all three spatial dimensions. As dehydration proceeds, polymer conformational compaction and pore structural reduction occur due to downward stresses resulting from the surface tension of the descending water interface coupled with strong water-polymer and polymer-Additive solute interactions. The stability of the porous structure was found to be enhanced by increased polymer chain density and by the presence of the additive solute which functions as a filler in the pore space and interacts strongly with the polymer chains and water molecules of the porous material. During dehydration, the descending water level tends to accumulate the additive molecules at the vapor-liquid interface, which form dense clusters of polymer chains at the interface, reduce the level of structural reduction, and increase the energy requirement for water removal. This phenomenon suggests that dehydration could be employed as a means to construct porous media with desirable spatial nonuniform density distributions of adsorption sites/ligands or catalyst sites/enzymes as the dissolved solutes. Extensively dehydrated porous structures were found to have substantially improved stability so that the water molecules introduced during the rehydration process expand slightly the dehydrated porous structure of the systems examined here but could not recover the original pore structures that existed before the commencement of dehydration; the findings of this work suggest that the original pore structures could be reduced less during dehydration and could be recovered more effectively during rehydration, if cross-linking reagents or extender molecules with elongated shapes are parts of the original polymeric porous material or incorporated later as additive solutes. The exterior aqueous phase was found to be capable of relaxing the dense interfacial clusters of dehydrated polymer chains and redissolving the additive molecules accumulated at the interface during dehydration. The approach presented here could form a basis for the systematic evaluation of the physicochemical effects of additive components on the polymeric porous structures and their stability from the extent of water-polymer, water-water, water-Additive solute, polymer-polymer, and polymer-Additive solute interactions during dehydration and rehydration, and it could also provide a molecular level design method of chemical engineering science for mechanistically controlling the structure and morphology of polymeric porous media as well as the spatial distribution of additive solutes in such media during dehydration and rehydration.

Department(s)

Chemical and Biochemical Engineering

Keywords and Phrases

Chains; Chemical Stability; Dehydration; Filled Polymers; Molecular Dynamics; Molecules; Phase Interfaces; Pore Structure; Porosity; Porous Materials; Potassium Sorbate; Reduction; Water Levels; Cross-Linking Reagents; Molecular Dynamics Modeling; Physicochemical Effects; Polymeric Porous Materials; Structural Reduction; Structure and Morphology; Systematic Evaluation; Vapor-Liquid Interfaces; Polymers

International Standard Serial Number (ISSN)

0888-5885

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2016 American Chemical Society (ACS), All rights reserved.

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