This report presents a study of electrokinetic transport in a series of integrated macro- to nano-fluidic chips that allow for controlled injection of molecular mixtures into high-density arrays of nanochannels. The high-aspect-ratio nanochannels were fabricated on a Si wafer using interferometric lithography and standard semiconductor industry processes, and are capped with a transparent Pyrex...

Speciation of arsenic (As) in well water and contaminated soil in the blackfoot disease endemic area has been studied by extended X-ray absorption fine structural (EXAFS) spectroscopy in the present work. Experimentally, we found that arsenic in the well water possessed an As-O bond distance of 1.72 A with a coordination number (CN) of 4.3. In the blackfoot disease area, arsenic with a high oxi...

In this paper, a general electrokinetic theory for concentrated suspensions in salt-free media is derived. Our model predicts the electrical conductivity and the electrophoretic mobility of spherical particles in salt-free suspensions for arbitrary conditions regarding particle charge, volume fraction, counterion properties, and overlapping of double layers of adjacent particles. For brevity, h...

A uniform-field design approach can improve the performance of microanalytical, chip-based devices for a number of applications, including separations and sample preparation. The faceted prism paradigm allows the design of microfluidic devices possessing spatially uniform fields in electrokinetically driven flows. We present the first quantitative study of the velocity fields obtained using fac...

Electrokinetic transport in fluidic channels facilitates control and separation of ionic species. In nanometer-scale electrokinetic systems, the electric double layer thickness is comparable to characteristic channel dimensions, and this results in nonuniform velocity profiles and strong electric fields transverse to the flow. In such channels, streamwise and transverse electromigration fluxes ...

Numerical solutions of the standard electrokinetic model provide a basis for interpreting a variety of electrokinetic phenomena involving ‘bare’ colloids. However, the model rests on the classical notion of a shear or slipping plane, whose location is unknown when surfaces are coated with permeable polymer. Consequently, an electrokinetic model for ‘soft’, ‘hairy’ or ‘fuzzy’ colloids has been d...

This report represents the completion of a two-year Laboratory-Directed Research and Development (LDRD) program to investigate miniaturized systems for chemical detection and analysis. The future of advanced chemical detection and analysis is in miniature devices that are able to characterize increasingly complex samples, a "laboratory on a chip". In this concept, chemical operations used to an...

Due to the increasingly wide application of electroosmotic flow in micromachines, this paper investigates the electroosmotic flow of the power-law fluid under high zeta potential in a cylindrical microcapillary for different dimensionless parameters. The electric potential distribution inside a cylindrical microcapillary is presented by the complete Poisson-Boltzmann equation applicable to an a...

Because of the diversity of streaming potential and zeta potential values reported in the literature, even for similar membranes and external conditions (hydrodynamics and solution chemistry), the influence of measuring cells and procedures in electrokinetic parameters has been studied. For this purpose, two different experimental systems (named EKA and NIS) with similar hydrodynamic parameters...