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

A photo 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 degrees C (> LCST)-visible light to 10 degrees C (< LCST)-ultraviolet light, the water contact angle (WCA) decreases rapidly from 142.4 degrees to 18.1 degrees. 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.

Automated summary

A photo and thermal-responsive smart polymer with controllable wettability was developed in this study, which enables reversible transitions between hydrophobic and hydrophilic states through temperature and light manipulation, offering great potential for various applications.