Abstract
Hysteresis is observed in sorption-induced swelling in various soft nanoporous polymers. The associated coupling mechanism responsible for the observed sorption-induced swelling and associated hysteresis needs to be unraveled. Here we report a microscopic scenario for the molecular mechanism responsible for hysteresis in sorption-induced swelling in natural polymers such as cellulose using atom-scale simulation; moisture content and swelling exhibit hysteresis upon ad- and desorption but not swelling versus moisture content. Different hydrogen bond networks are examined; cellulose swells to form water–cellulose bonds upon adsorption but these bonds do not break upon desorption at the same chemical potential. These findings, which are supported by mechanical testing and cellulose textural assessment upon sorption, shed light on experimental observations for wood and other related materials.
Highlights
Hysteresis is observed in sorption-induced swelling in various soft nanoporous polymers
Altogether, our results show that hysteresis observed in sorptioninduced swelling of amorphous cellulose stems from different coupled microscopic hydrogen bond network/cellulose energy landscapes upon adsorption and desorption
This means that the hysteresis is not due to hydrogen bonding itself but to a complex coupling between the fluid grand free energy and the cellulose free energy
Summary
Hysteresis is observed in sorption-induced swelling in various soft nanoporous polymers. 1234567890():,; Soft nanoporous matter is an important field which encompasses anthropic materials such as compliant porous solids, foams, intrinsically porous polymers, organic membranes, etc[1,2,3], as well as natural materials such as wood, bamboo, plants, linen, kerogen in gas shale, etc[4,5,6,7,8] Owing to their large internal surface area and compliant skeleton, strong coupling between fluid configurations and deformation of these materials leads to sorption-induced swelling that can be accompanied with large hysteresis. By using a hybrid strategy combining GCMC and MD, the atomic simulations reported here probe adsorption phenomena while allowing for deformations and internal stress relaxation of the host porous polymer Such microscopic simulations can explicitly account for the coupling between deformation of the porous material and water sorption. The intercellulose hydrogen bonds, broken upon water adsorption, reform at a much lower relative humidity leading to a large hysteresis
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