Understanding the behavior of stimuli-response ionogels for microfluidic applications

Abstract

Electrochemical Impedance Spectroscopy (EIS) studies of two different ionogels (IOs) are performed using gold interdigitated electrodes (Au-IDEs). Poly(N isopropylacrylamide) (pNIPAAM) is polymerized in the presence of two ionic liquids (ILs), ethyl- 3-methylimidazolium ethyl sulfate [C2mIm][EtSO2] (1) or trihexyltetradecyl-phosphonium dicyanamide [P6,6,6,14][DCA] (2). The Nyquist diagrams of the IOs reflect significant differences due to their polarity and porosity dissimilarities. This fact is supported with the study of the diffusion of water through the polymer matrix, which is faster for IO-1, the most porous IO. Moreover, the ability of IO-1 and IO-2 to conduct current is measured and the sheet resistance of IO-2 is two orders of magnitude higher than IO-1. Finally, the swelling/drying properties of the IOs are monitored exposing them to several vacuum and rehydration cycles. The Nyquist plot of IO-1 shows faster diffusion and recovery of the original properties. Both hydrophilicity and porosity are in the basis of these results.