Investigating\nthe Water-Induced Stiffening Mechanism\nin a Novel Polyurethane through Simulation and Experimental Analysis

Much attention has been drawn to our previously reported\npolyurethane\nfeaturing a hard backbone and dangling poly(ethylene glycol) (PEG)\nsoft segment. It is endowed with a unique self-stiffening property\nwhen exposed to water. Yet the mechanism from a molecular perspective\nis still not quite clear. Herein, coarse-grained (CG) and all-atom\n(AA) molecular dynamics (MD) simulations, alongside experimental approaches,\nhave been employed to unravel the mechanism behind the phenomenon.\nIt is confirmed that water could induce the polyurethane to achieve\na higher degree of phase separation. When being stretched, hard domains\nof aqueous side chain PEG polyurethane (SPPU) have a stronger tendency\nto orient in the direction of tensile stress and facilitate the effective\ntransfer of stress. This enhancement effect of water-stiffening cannot\nbe achieved at an insufficient side chain density. The ratio of hydrogen\nbonds in the SPPU exhibited a higher degree of enhancement with water\ncontent, which is in accordance with experimental results. The unique\ntopology of SPPU was considered to be the most important factor to\nthe Young’s modulus determined by the gradient boosting regression\n(GBR) model. This research helps to advance our comprehension of the\ninterplay between the structure and performance of polyurethane, providing\na theoretical foundation for the design of a novel material.