Reversible photo-/thermoresponsive structured polymer surfaces modified with a spirobenzopyran-containing copolymer for tunable wettability

Photo-/thermoresponsive surfaces that consist of thin layers of crosslinked poly(N-isopropyl acrylamide) functionalized with photochromic spirobenzopyran grafted from the cyclic olefin copolymer substrates are reported. These films act as intelligent hybrid films whose wettability can be reversibly manipulated by simple incandescent light irradiation or temperature changes. Such reversible wettability was augmented by the introduction of surface microstructures, and even further enhanced by the incorporation of nanorods with the static contact angle change being 5 degrees to 123.1 degrees. A simple and effective method was developed to construct polymeric surface microstructures via solvent vapor induced crazings. The light-induced wettability change can be attributed to the synergistic effect between photoisomerization of the spirobenzopyran chromophore and the dehydration of the poly(N-isopropyl acrylamide) main chain. The long-term stability of the reversible surface wettability switch was realized by using incandescent light illumination instead of laser irradiation. An intriguing phenomenon known as the Cassie-Wenzel wetting transition occurred on the nanorod-structured surface modified with the photo-/thermoresponsive copolymer films at ambient conditions without external triggers.