Photoplasticization Behavior and Photoinduced Pressure-Sensitive Adhesion Properties of Various Polymers Containing an Azobenzene-Doped Liquid Crystal

Abstract Photochemical control of the hardness and fluidity of polymeric materials is applicable to the development of photoreversible adhesives. Here, we report that common polymers show photoplasticization behavior, which is the photoinduced reduction of the glass transition temperature, just by adding an azobenzene-doped liquid crystal (azo-doped LC). We found that the photoplasticization effect that occurred in amorphous polymers with an azo-doped LC was due to a microscopic phase separation of the azo-doped LC from the polymers. In contrast, we did not observe any photoplasticization behavior in crystalline polymers because of the macroscopic segregation of the azo-doped LC from the polymers and high rigidity of the crystalline regions of the polymers. Based on the photoplasticization effect, we successfully achieved photochemical induction of tackiness, which is a pressure-sensitive adhesion property. Furthermore, the maximum tack strength was enhanced upon photoirradiation of the polymers. We inferred that this behavior originated from an increase in the interaction between the samples and the test probe based on the change in polarity of the samples by the photoisomerization of azobenzene. We conclude that “photoplastic” polymers composed of common materials can be used for photoresponsive pressure-sensitive adhesives.