Conformational changes at polymer gel interfaces upon saturation with various liquids studied by infrared-visible sum frequency generation vibrational spectroscopy

Molecular restructuring at the free surface of poly(2-hydroxyethyl methacrylate) (PHEMA) films and the buried interface with a sapphire substrate due to submersion into deuterated water (D2O) and acetonitrile (d3ACN) was investigated by infrared-visible sum frequency generation (SFG) vibrational spectroscopy. Film hydration by saturation with D2O and d3ACN resulted in polymer swelling. Because of the amphiphilic nature of PHEMA, direct information about polymer restructuring was obtained due to the existence of hydrophilic and hydrophobic moieties. SFG results provided insight into the restructuring behavior at the PHEMA surface and buried interface upon swelling due to the diffusion of the two different liquids.