SURFACE-PROPERTIES OF TEMPERATURE-SENSITIVE N-ISOPROPYLACRYLAMIDE-COPOLYMER GELS

N-isopropylacrylamide-copolymer gels were synthesized with the monomers acrylamide (AcAm), N-isopropylacrylamide (NIPA) and N-acryloylpiperidine (APP) having different hydrophobicities. These gels showed hydration and dehydration according to thermal stimulus, namely a temperature change across the phase transition temperature (T(p)). The surface properties of gels were found to depend on both the molecular structure of the copolymer and the thermal stimulus through adsorption of benzoic acid and phthalic acid. These adsorbates were adsorbed at high temperature aboue T(p) and desorbed at low temperature below T(p) due to the change in hydrophobicity of the gel surface. The amount of adsorption increased linearly with the concentration of adsorbates, giving an isotherm of Henry type. The phase transition temperature (T(p)) of gel could be controlled by incorporation of AcAm or APP into NIPA. T(p) increased with incorporation of hydrophilic monomer (AcAm), while it decreased with incorporation of hydrophobic monomer (APP). The adsorption and desorption occurred quickly and reversibly in response to step-wise temperature change.