pH dependant coating for microfluidics devices
Keywords:Microfluidics, polyelectrolyte multilayers, EOF, PDMS.
AbstractThe layer-by-layer technique was used to coat the channels of PDMS microfluidics devices. The coating was based on the sequential deposition of polydiallyldimethylammonium chloride (PDADMAC) with a copolymer of polystyrene sulfonate and maleic acid (CoPSS-Maleic) into polyelectrolyte multilayer (PEM). The possible deposition of PEM coating on PDMS was confirm by contact angle which showed the clear transformation of the PDMS surface from hydrophobic to hydrophilic. The later deposition of the PEM coating inside the micro-channels was confirmed by change in electroosmotic flow direction (EOF) and intensity as a function of the number of deposited layers. The EOF measurements revealed that after the deposition of only 2 layers, the flow direction and intensity already reached its maximum value oscillating between â€“2.5x10-4 cm2/V.S and 4.1x10-4 cm2/V.S as a function of the positive or negative top layers of the coating. The changes in EOF value as a function the pH in the solution were also investigated. The intensity of the electroosmotic flow was influenced by the pH of the solution, which affects the charge density at the surface of the PEM coating. This property can be used to tune the separation resolution, which is the missing parameter in uncoated PDMS chip.
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