Thermal-Responsive Block Copolymers for Surface with Reversible Switchable Wettability

A series of thermal-responsive block copolymers, i.e., poly(methyl methacrylate)-block-poly(N-isopropylacrylamide) (PMMA-b-PNIPAAm), were successfully synthesized via successive copper(0)-mediated reversible-deactivation radical polymerization technology. Thermal properties of block copolymers with different PNIPAAm chain lengths were investigated by differential scanning calorimetery (DSC) and thermogravimetric analysis (TGA). The well-separated glass transition temperature values shown in DSC results indicate that two chemically different blocks, PNIPAAm and PMMA, are incompatible and phase-segregated. The thermal degradation results show that the thermal stability of these copolymers was improved through incorporating the PNIPAAm segments. The PMMA120-b-PNIPAAm86 and PMMA120-b-PNIPAAm130 maintain stability and undergo one-stage degradation when the temperature increases above 360 degrees C. Because of the synergistic effect of copolymer composition and copolymer film roughness, the obtained reversible thermal-responsive wettability for the resulting copolymer-modified surfaces is different, which is enhanced by incorporating more functional NIPAAm units. Specifically, the variations of the static water contact angle for the surfaces fabricated by PMMA120-b-PNIPAAm40, PMMA120-b-PNIPAAm54, PMMA120-b-PNIPAAm86, and PMMA120-b-PNIPAAm130 are 18.7, 20.4, 26.8, and 34.3 degrees, respectively. In addition, all as-prepared surfaces present a stable reversible thermal-responsive wettability, which can be applied to coatings with temperature-controllable wettability as well as manipulation of liquids in microfluidic devices.