Sono-respond on thermosensitive polymer microgels based on cross-linked poly(N-isopropylacrylamide-co-acrylic acid)

Ultrasound (US) exposure strongly influenced thermosensitivity of microgels attracted with both N-isopropylacrylamide (NIPAM) and acrylic acid (AA) segments, due to that hydrogen bonds of carboxylic acid segments in microgels were broken by US and then the hydration with water occurred. US induced critical effects on the volume phase transition temperature of the swelled NIPAM gel (PNAM). It was observed after the US exposure that the particle size was increased and the phase transition of the microgels shifted toward larger temperature regions of the hydrodynamic diameter. FT-IR spectroscopic data of the swelled microgel showed that the free OH stretching band intensity of the COOH segments was enhanced by the exposure, but the band intensity returned to its original level without the US exposure. This meant that the US stimulus broke hydrogen bonding of the microgel and induced hydration of water in the hydrogel environment. Finally, regeneration of the hydrogen bonds in the microgel was occurred after the US exposure.