Mechanical Properties and Moisture Transport Behavior of Acid-Sensitive Hydrogels

Thin hydrogel films containing the acid sensitive cross-linker 2,5-dimethyl-2,5-hexanediol dimethacrylate (DHDMA) were synthesized as part of a larger project to create protective layers against chemical and biological (CB) threats. In order to operate efficiently as fabric coatings, the mechanical and moisture vapor transport properties of these materials must be understood. The hydrogels were composed primarily of poly(ethylene glycol) dimethacrylate (PEGDMA) and 2-hydroxyethyl methacrylate (HEMA) and were prepared by free radical cross-linking polymerization. The influence of different compositions of DHDMA, PEGDMA, and HEMA on the moisture vapor transmission rate (MVTR), mechanical properties, and swelling properties of PEGDMA/DHDMA/HEMA copolymer hydrogels has been investigated. The characterization by Fourier transform infrared (FTIR) spectroscopy confirmed the presence of all monomers used in the gel structure. The hydrogels showed high MVTR, which are comparable to the widely accepted breathable membrane of Gore-Tex fabric and expanded polytetrafluoroethylene (ePTFE). The swelling data indicated that the equilibrium water content depends on the composition of hydrogels. It was found that addition of HEMA into the PEGDMA-based hydrogels was very helpful to improve the swelling properties but decrease in water contact angle. Rheological study of hydrogels showed that the hydrogels are very stiff and their stiffness increases with increasing PEGDMA content in the hydrogels.