Microfluidic Valves Comprising Nanolayered Thermoresponsive Polymer-Grafted Capillaries

摘要

To control fluid behavior within microchannels for reliable microfluidics processing, simpler, more effective flow-valve designs are required. We describe novel microflow valves produced not by scaling down conventional valve designs, but rather by exploiting thermally induced changes in the surface properties of ultrathin grafted polymers, which lead to changes in the bulk hydration structure. Our microfluidics valve design comprises nanometer-sized surface-grafted ther-moresponsive poly(N-isopropylacrylamide) (PIPAAm) layers within microcapillaries. These surfaces exhibit rapid aqueous wetting alterations over convenient temperature ranges through hydration changes in the PIPAAm grafts. Hydration of PIPAAm-grafted chains at the capillary interfaces increases the microviscosity of the hydration layers at the wall interfaces without physically occluding the capillary lumen, significantly influencing flow frictional resistance, and producing complete and reversible on-off flow valving in microchannels under relevant hydrostatic pressures useful for microfluidics approaches.