Spiropyran-based photo- and thermal-responsive smart polymer with controllable wettability

Abstract

and thermal-responsive smart polymer, enabling controllable wettability according to different temperature and light conditions, was developed in this paper. The 3-(3′,3′-dimethyl-6-nitrospiro-[chromene-2,2′-indolin]-1′-yl) propyl methacrylate (SPMA) and N -isopropylacrylamide (NIPAAm) by 2,2′-azobis(isobutyronitrile) (AIBN) were grafted on the surface of polydimethylsiloxane (PDMS) to induce free radical polymerization. The SPMA isomerizes from a colorless, hydrophobic spiropyran (SP) form to a deep purple, hydrophilic merocyanine form (MCMA) upon UV-light. The wettability of poly( N -isopropylacrylamide) (PNIPAAm) is sensitive to temperature, showing hydrophobicity above the low critical solution temperature (LCST) and hydrophilicity below LCST. Furthermore, the addition of SPMA has realized the significant reversible wettability synergistic with PNIPAAm. The reversible wettability can be controlled by selectively applying single or both factors of light and temperature. Thus, practical application of the above controllable wettability can be greatly expanded. When the polymer is transferred from 40 °C (>LCST)-visible light to 10 °C (<LCST)-ultraviolet light, the water contact angle (WCA) decreases rapidly from 142.4 ° to 18.1 ° . Such excellent hydrophobic-hydrophilic transition can be achieved by UV-light excitation for only 15 s and maintains good repeatability over 10 hot-cold cycles and 20 light cycles without performance loss. • Light and heat are both clean energy available in nature. • The light response time greatly shortened, the reversible wettability switching effect enhanced. • Photothermal dual response membrane, wide response range, strong reversibility, good repeatability.