Influence of crosslink on the formation of hydrophobic hydrogels

Abstract

Recently invented hydrophobic hydrogel is a specific type of soft matter, which is composed of purely hydrophobic networks while maintaining ultra-high water content. Owing to their unique structures, hydrophobic hydrogels manifest various particularities for versatile applications. Therefore, it is essential to reveal the factors that determine the gels’ formation. Until now, the role played by the chemical crosslinks (e.g. crosslink ratio, structure) stays unclear. To figure out the mystery, herein we prepare a series of polyacrylate gels with different crosslinks at diverse crosslinker concentrations. Upon being soaked in water, the gels behave divergently in terms of dynamic swelling behavior. Unlike conventional gels, the maximum swelling degrees of three different hydrophobic hydrogels initially increase and then decrease with raising in crosslink ratio. Similarly, the swelling kinetics significantly vary with the crosslink ratio. From the data, a moderate crosslink ratio is required for the formation of hydrophobic hydrogels as it endows the polymer chain with high mobility and density. In addition, the chemical structure of crosslinks plays a less significant role in the formation of hydrophobic hydrogels but an important role in determining their swelling equilibrium states in water, which ultimately affects their mechanical performance. All these results may help us to uncover the formation mechanism of the hydrophobic hydrogels and establish a general standard for the preparation of such soft matter.