Effect of hydrophobic substances on the volume-phase transition of N-isopropylacrylamide gels

The effects of the addition of hydrophobic substances on the volume-phase t ransition of N-isopropylacrylamide (NIPA) hydro gels were investigated. The volume transition temperature of NIPA gel was reduced by adding hydrophobi c substances, such as benzoic acid (BA) and phenol (Ph), into the solution surrounding the gel. The degree of binding of BA or Ph to the NIPA gel was found to increase in a transition-like manner simultaneously with discontin uous volume shrinkage. The lowering of the transition temperature relates t o the degree of binding of BA and Ph to the NIPA gel in the collapsed state . Fourier transform infrared (FTIR) spectra of the Ph binding gel suggest t hat the hydrogen bond forms between the amide group of the NIPA and the hyd roxyl group of Ph.