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A thermo-electro-hydro-dynamic model is developed to analytically account for the effects of Stern layer conductance on electrokinetic energy conversion in nanofluidic channels. The optimum electrokinetic devices performance is dependent on a figure of merit, in which the Stern layer conductance appears as a nondimensional Dukhin number. Such surface conductance is found to significantly reduce the figure of merit and thus the efficiency and power output. This finding may explain why the recently measured electrokinetic devices performances are far below the theoretical predictions where the effects of Stern layer conductance have been ignored.

A general model based on the Onsager reciprocal relations is developed to study the streaming potential and streaming current in heterogeneous microchannels. The surface heterogeneities may be symmetrically or asymmetrically distributed parallel or perpendicular to the flow axis. Both streaming effects are modified by the flow rate through the heterogeneous channel, to eliminate the possible influence of electrokinetic flow on the streaming potential and streaming current measurements. Although they are still dependent on the distribution of surface heterogeneity, the flow rate-modified streaming effects are demonstrated to provide more consistent results with the traditional linear assumption than do the traditional ones, especially apparent in small microchannels.

Presented herein is an Onsager reciprocal relations-based thermodynamic analysis of the electrokinetic transport of fluids and ions in micro/nanofluidics. This analytical approach provides a straightforward understanding of electrokinetic energy conversion, streaming potential and streaming current measurements, and electrokinetic flow control in micro/nanoscale channels or networks.

We successfully demonstrate that DC dielectrophoresis can be utilized to separate particles of three dissimilar sizes simultaneously in a microfluidic chip. This continuous-flow separation is attributed to the particle size dependent dielectrophoretic force that is generated by the non-uniform electric field around a single insulating hurdle on the channel sidewall.