Swelling and Exchange Behavior of Poly(sulfobetaine)-Based Block Copolymer Thin Films

The humidity induced swelling and exchange behavior of a block copolymer thin film, which consists of a zwitterionic poly(sulfobetaine) (PSPP) block and a nonionic poly(N-isopropylacrylamide) (PNIPAM) block, is investigated by time-of-flight neutron reflectometry (TOF-NR). We monitor in-situ the swelling in H2O vapor followed by an exchange with D2O. In the reverse experiment, swelling in D2O vapor and the subsequent exchange with H2O is investigated. Both, static and kinetic TOF-NR measurements indicate significant differences in the interactions between the PSPP-b-PNIPAM thin film and H2O or D2O, which we attribute to the different H- and D-bonds between water and the polymer. Changes in chain conformation and hydrogen bonding are probed with Fourier transform infrared (FTIR) spectroscop y during the kinetic processes and reveal the major role of the ionic SO3- group in the PSPP block and the polar amide groups of both blocks during water uptake and exchange