Aqueous elution control in wettability modulated microchannels grafted with thermoresponsive polymers

Temperature-dependent aqueous wettability of poly(N-isopropylacrylamide) (PIPAAm)-grafted surfaces was regulated by grafted polymer layer thickness and basic hydrophobicities of the polymer-grafted surfaces. Thermoresponsive surfaces with controlled polymer layer thickness were prepared by surface-initiated atom transfer radical polymerization (ATRP). Static contact angles for both surfaces were drastically changed in response to temperature alteration. Hydrophilic property of PIPAAm-grafted surfaces depends on polymer layer thickness at low temperature range. More hydrophobic surface properties were observed for poly (n-butyl methacrylate) (PBMA)-b-PIPAAm-grafted surfaces than IPAAm homopolymer-grafted surfaces above PIPAAm's transition. The changes of static contact angles for both surfaces were drastically changed in response to temperature alteration temperature. Well-defined thermoresponsive microchannels were then fabricated for elution control of steroids through the modulation of surface characteristics by temperature. Using PIPAAm-grafted hollow capillaries, baseline separation of steroids was successfully achieved within 10min by changing only temperature. Furthermore, the hydrophobic testosterone showed stronger hydrophobic interaction on more hydrophobized PBMA-b-PIPAAm-grafted surfaces above the PIPAAm's transition temperature.