Tuneable swelling of thermo- and pH-responsive copolymer films

Abstract

We report on thermo- and pH-responsive copolymer films consisting of N-isopropylacrylamide (NIPAAm) and different carboxyalkylacrylamides exhibiting switchable swelling states over a wide range of temperatures and pH-values. The copolymers were covalently grafted as brush-like films onto solid substrates. Analysis by quartz crystal microbalance with dissipation monitoring revealed the phase transition behaviour to be sensitively controlled by the balance of polar and non-polar interactions, which could be dissected into the local level of comonomer structure as well as the more global level of copolymer chain composition. Remarkably, the phase transition was determined to be in general lower than in solution, which originated from the higher local polymer concentration of the swollen surface-grafted copolymer layer as explained by the general phase behaviour based on classical theory of polymers in solutions. The different swelling profiles of the environmentally responsive copolymer films are expected to offer valuable options for the design of switchable interfaces as, for instance, applicable for the modulation of model biosystems.