Volume-Phase Transitions in Photo-Crosslinked, Surface-Tethered LCST Polymer Networks

Volume-phase transitions and thermoshrinking properties have been studied for a series of N-alkylacrylamide polymers. The surface-tethered networks were prepared by photo-crosslinking thin films of co-polymers that contain photoactive benzophenone-pendant segments. The structure of alkyl group was found to have a pronounced effect on both the lower critical solution temperature (LCST) and thermoshrinking properties. Quartz-crystal microbalance with dissipation monitoring (QCM-D) and ellipsometry were used to investigate the volume-phase transitions. We show how thickness, shear elastic modulus, and shear viscosity of the polymer films can be obtained by the QCM-D technique, even beyond the so-called Sauerbrey regime. QCM-D was also employed to examine the effect of temperature and the influence of the Hoffmeister salt series on the LCST of N-alkylacrylamides polymers.