Temperature-sensitive surfaces prepared by UV photografting reaction of photosensitizer and N-isopropylacrylamide

A thermal-sensitive surface was prepared on the surface of a silicone wafer (substrate) by an ultraviolet photografting reaction between a photosensitizer, (N,N'-diethylamino)ditkiocarbamoylpropyl(trimethoxy)silane, and N-isopropylacrylamide. Ellipsometery measurement revealed a thin grafting layer (similar to 44 Angstrom) consisting of a single terminal poly(N-isopropylacrylamide) (PNIPAAm) chain on the surface of the silicone wafers. X-ray photoelectron spectroscopy confirmed that the grafting layer was composed of the PNIPAAm structure. The properties of the grafting layer can be adjusted and manipulated by varying the photopolymerization time and the concentration of the monomer. Increasing the photopolymerization time and the concentration of the monomer increases both the thickness of the grafting layer and the wettability of the surface. The characteristics of the temperature-sensitive surface were investigated by dynamic contact angle as a function of temperature. The remarkable change on advancing contact angle can be observed around 32 degreesC. Compared with the substrate grafted by PNIPAAm gel, the substrate with a signal-terminal PNIPAAm chain exhibited a lower transition temperature and a narrower change range of transition temperature. This can be attributed to the mobile PNIPAAm chain with a single-terminal mode, which increases the characteristics of faster response to the temperature change.