Flow control in microfluidics using photo-sensitive polymer

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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.