Flow control in microfluidics using photo-sensitive polymer

提出了一种在微流体中切换液体流动的新方法。该方法是基于通过对壁面润湿性的刺激响应控制来显著改变水进入狭窄液路的程度。水溶性聚合物聚（at -异丙基丙烯酰胺）[PNIPAAm]脱水，加热超过其较低临界溶解温度后变为水不溶性；ca。32℃。当PNIPAAm被涂覆在玻璃表面时，这种独特的性质被成功地用于制造具有不可逆润湿特性的表面。通过甲基丙烯氧基丙基三甲氧基硅烷（粘结硅烷）的偶联，再用过硫酸铵和N，N，N，N -四亚甲基乙二胺进行N-异丙基丙烯酰胺和双丙烯酰胺的氧化还原聚合，制备聚合物涂层。傅里叶变换红外光谱显示在玻璃表面成功地涂覆了聚合物。在室温下，聚合物涂层玻璃表面的水接触角约为30度。另一方面，在40℃时，角大于70度，与聚苯乙烯相对应。在40℃下，抑制了30 mm的200'mm玻璃毛细管的毛细。这一事实表明，困难在于水引入到pnipaam涂层毛细管。用加热元件加热或激光照射可使温度升高。通过将涂膜玻璃毛细管的加热部分改变到分支下游，成功地实现了分支毛细管中液体流动的切换。

A novel method for switching liquid flow in microfluidics was developed. The method was based on significant change in the extent of water introduction into narrow liquid path by the stimuli-responsive controle of wettability of the wall surface. Water-soluble polymer, poly(AT-isopropylacrylamide) [PNIPAAm] , was dehydrated and thus becomes water-insoluble on heating above its lower critical solution temperature ; ca. 32℃. Such unique natures of PNIPAAm was successfully used for the manufacturing the surface having irrevesible wetting properties, when the polymer was coated onto a glass surface. The polymer coating was performed by the coupling of methacryloxypropyltrimethoxysilane (Bind-silane) and the subsequent redox polymerization of N-isopropylacrylamide and bisacrylamide using ammonium persulfate and N,N,N,N -tetramethylethylenediamine. An FT-IR spectrum showed successful polymer coating on glass surfaces. A water contact angle of polymer coated glass surface was approximately 30 degree at room temperature. On the other hand, the angle become more than 70 degree at 40℃, being corresponding to that for polystyrene. The capillarity of 200'mm glass capillary, 30 mm, was depressed at 40℃. This fact suggests that the difficulties lie in the water introduction into the PNIPAAm-coated capillary. The temperature could be risen by warming with heating elements or irradiation of laser light. The switching of liquid flow in branched capillary was successfully performed by change the heating portion of the polymer-coated glass capillary downstream a bifurcation.