Effects of infrared irradiation on polymer gels

An infrared laser has been used as an external stimulus to trigger phase transitions in neutral and ionic N-isopropylacrylamide (NIPA) gels. It is found that the infrared laser can cause the gels to undergo changes in volume, shape and transparency, with response times of the order of hours, minutes and seconds, respectively. All of the changes observed are completely reversible. The experimental results can be explained by considering the infrared laser as a point heating source which raises the sample temperature locally above its volume phase transition value. The above effects raise the possibility of gel devices and sensors whose properties are controlled by infrared lasers.