Dynamic light scattering study of poly(N-isopropylacrylamide-co-acrylic acid) gels

Spatial inhomogeneities of poly(N-isopropylacrylamide-co-acrylic acid) (NIPA/AAc) gels were investigated by dynamic light scattering as a function of AAc comonomer concentration and temperature. The results showed the following: (1) The ensemble average scattered intensity, [I](E), decreased with increasing AAc comonomer concentration and increased with temperature. (2) Dynamic fluctuations increased with temperature and diverged at the transition temperature, T-c. (3) Above the Theta temperature of NIPA homopolymer in an aqueous solution, the intensity-intensity time correlation function did not fit a single-exponential function, but fit a double exponential or a stretched exponential, indicating a heterogeneous structure, i.e., polymer-rich and polymer-poor phases at temperatures above Theta.