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Microfluidics offers methods of miniaturization for numerous chemical, electrochemical and biological processes. Thermal diffusion of molecular species through microfluidic channels is involved in many of such processes. High specific surface in microchannels complicates the theoretical assessment of diffusion rate in such channels as both the diffusion coefficient and the physisorption rate to the channel walls are temperature-sensitive. In this work, it is shown that both of these parameters vary in the same direction with temperature and the superposition of their respective effects makes the process rate highly temperature-sensitive. The molecular diffusion rates for three different molecular species, 2-butanol, tert-butanol and hydrogen, through a centimeter-long microchannel are experimentally monitored at the ambient temperature. Repeating such recording at different ambient temperatures facilitates the measurement and comparison of the temperature sensitivities of these processes. Among the fluids examined, those with lower diffusion coefficients showed more significant temperature dependences. The fabrication of the microfluidic system and the method utilized for monitoring the diffusion rate are also described in this paper.

Obtaining information on the nature of ionic species in electrolyte samples is in demand. The examination process must take less than ~1 min, and the test is expected to require small volume (micro-liter) samples. Here, we report electrolyte examination results with a simple voltammetry process carried out on thin film indium tin oxide micro-electrodes deposited on polyethylene terephthalate substrates and micromachined by CO2 laser ablation. The sample volume required is 2 μl, which is dropped manually on the electrodes with a sampler. The voltage waveform applied between the electrodes is a combination of positive and negative pulses of different magnitudes. The transient electric current passing through the electrolyte is monitored and plotted versus time. These plots are utilized as the finger prints of the related electrolyte samples. Pattern recognition methods are employed for information extraction from the obtained patterns. The diagnostic information extracted from these patterns proved sufficient for discrimination among KF, KCl and KI samples at various concentrations.