Investigating the Water-Induced Stiffening Mechanism in a Novel Polyurethane through Simulation and Experimental Analysis

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