Manipulate fluid in microchannels with thermo-responsive film Original Research Article

The improvement of thermo-responsive wettability change on the glass surfaces poly(N-isopropylacrylamide) [PNIPAAm]-modified was investigated by the cooperative modification with hydrophobic octadecylsilane (ODS) or by the polymer modification on frosted surfaces. The water contact angle of PNIPAAm-modified glass surface was ca. 32° below the lower critical solution temperature (LCST, ca. 32 °C) of PNIPAAm, while it was ca. 68° above LCST. In PNIPAAm–ODS system, the water contact angle above LCST increased to ca. 84°, but was still lower than 90° being the measure of water-repellency. On the other hand, higher wettability (water contact angle; ca. 24°) below LCST and water-repellency (water contact angle; ca. 104°) above LCST were obtained on the PINIPAAm-modifed frosted glass surfaces. When an optional portion beside the channel on a glass plate was warmed, the capillarity-based liquid flow in the channel was temporary stemmed at the prescribed portion. Furthermore, the flow switching at a T-junction in the channel was successfully achieved, when the opposite side of the channel that stream had to be directed was warmed.