Thermoresponsive Behavior of Poly(N-isopropylacrylamide) Solid Ultrathin Film under Ordinary Atmospheric Conditions

Significant changes in the thickness of poly(N-isopropylacrylamide) solid ultrathin films have been observed by X-ray reflectivity as a result of changing the temperature between 15 and 60 °C in an uncontrolled atmosphere. As the property of the film switches between hydrophobic and hydrophilic nature at around 33 °C, the present letter reports that an ultrathin film of around 200 Å exhibits nearly a 7% change in thickness even in an ordinary atmosphere and that cooling and heating exhibit different dependence; i.e., one can confirm the switching point in the cooling run, but the dependence is linear in the heating run. The phenomena are reproducible and repeatable.