UC Davis

Although alternating current (AC) unimodal electrokinetics are studied extensively in a variety of microfluidic and fabrication processes, linearized electrokinetic models fail to comprehensively capture the complex dependency on the electrolyte identity. Recent nonlinear numerical studies indicate the existence of nonzero time-average electric fields, called asymmetric rectified electric fields (AREFs), which arise from the ion mobility mismatch of the electrolyte. Further, the application of a multimodal field has been theorized to break the spatial symmetry of AREF, yielding net particle drift in the bulk fluid. While some experimental evidence implicates AREF-driven electrokinetics, the connection between AREFs and many experimentally observed phenomena remain untested. This dissertation presents a broad assessment of AREFs in particle aggregation and particle net drift in microfluidic channels under unimodal and multimodal polarization. Estimates of an AREF-induced steady flow coupled with previous AC electrokinetic theory provide a scaling explanation on the electrolyte-dependent aggregation or separation behavior near electrode surfaces. Further, observed particle distributions using a microchannel configuration agree with numerical AREF predictions predicated on electroosmotic flows arising on the particle and channel wall surfaces.

These results served as a motivation to investigate temporal symmetry breaking in vibrating systems with solid-solid friction to enable “vibrofluidic” manipulation of granular materials. Both experimental and theoretical results demonstrate that multimodal vibrations induce transport of dry granular media in a desired direction, while mixing and separation operations are achieved using various channel geometries or waveform properties. Both the electrokinetic and vibrofluidic results suggest that multimodal driving forces may pertain to a broad range of other useful applications.