PNNL

Abstract

Temperature-sensitive surfaces were prepared by grafting polyN-isopropylacrylamide (PNIPAAm) hydrogel on the surface of silicone wafers. The silicone wafers as the substrate were modified by organosilane (vinyltriethoxylsilane). They were further reacted with N-isopropylacrylamide (NIPAAm) using N, N'-methylenebisacrylamide as the crosslinking agent to generate the crosslinked PNIPAAm layer on the surface of the substrate. The surfaces modified by the crosslinked PNIPAAm layer were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and attenuated total reflectance-Fourier transform infrared. The reversible hydrophilic/hydrophobic properties of the surface were evaluated by dynamic contact angle. The morphology of the surface modified by a crosslinked PNIPAAm layer can be turned from "sea-island" to "mountain-valley" by changing the molar ratio of NIPAAm to BisAAm and by varying the polymerization time. The completely hydrophilic surface (advancing contact angle = 0?) was observed below 25?C, and the surface became extremely hydrophobic (advancing contact angle = 92?) above 40?C. The sensitivity of surfaces to temperature change can be improved by increasing the crosslinking density of the polymer layer and varying the polymerization time. The water meniscus height in a capillary tube, whose wall was coated by a crosslinked PNIPAAm layer, went up or down as the temperature changed to below or above the lower critical solution temperature of PNIPAAm. The differences of water meniscus height are 10 and 5 mm for the capillary tube with the diameter of 2 and 3 mm, respectively, corresponding to the change of temperature from 23?C to 50?C. The temperature-sensitive characteristics, which produce remarkable and rapid changes of surface properties, makes this technology applicable as actuators, modulators, sensors, and switches.