Direction Of Dc Electric Field Research Articles

Electrokinetic Trapping and Patterning of Colloidal Particles in Asymmetric Ratchet Microchannels

Insulator-based dielectrophoresis offers advantages over electrode-based dielectrophoresis in many ways, and has been extensively used to manipulate, sort and selectively trap particles and biological species in Lab-on-a-chip devices. This work exploits insulator-based dielectrophoresis in two configurations of asymmetric ratchet microchannels to trap microscale particles using DC biased AC voltages. It demonstrates for that dynamics of the DEP trapping zones changes in response to voltages higher than the threshold trapping voltages, and also with longer experimental runtimes. Numerical modeling is used to support and validate the results, and the physical interpretations of the changing DEP are explained using a dimensionless trapping number. With the help of the microchannel configurations, it is revealed that the orientation of the asymmetric ratchet relative to the direction of DC electric field plays a key role in determining the trapping patterns

Swelling, Shrinking, Deformation, and Oscillation of Polyampholyte Gels Based on Vinyl 2-Aminoethyl Ether and Sodium Acrylate

The behavior of amphoteric hydrogels based on vinyl 2-aminoethyl ether and sodium acrylate under the influence of pH, ionic and solvent composition, temperature, and dc electric field has been studied. The excess of positive or negative charges causes the swelling of polyampholyte networks. At the isoelectric point (IEP) the polyampholyte gel is in shrunken state due to the formation of intraionic contacts. An antipolyelectrolyte effect is observed at the IEP: the gel considerably swells in the presence of neutral salt. The condensation of bulky anions to positively charged groups of polyampholyte gels enhances the shrinking rate. The shrinking process can be described by apparent first-order kinetics. Polyampholyte gel shrinks with the increasing of temperature when the overall charge is neutral (IEP), while it shrinks effectively with addition of acetone when the overall charge is negative. In dependence of the network net charge, the ionic strength of the external solution, and the direction of dc electric field, the polyampholyte specimen can bend, shrink, swell, and oscillate. Under the same conditions, positively and negatively charged precursors of polyampholytes only swell or shrink. Shrinking and swelling of amphoteric gels are determined by the concentration of mobile ions inside and outside of gel. To interpret the oscillation phenomenon the Donnan equilibrium and water hydrolysis are utilized. The realization of antipolyelec-trolyte or polyampholyte and polyelectrolyte effects is probably the driving force of gel behavior. The oscillation-relaxation regimes are characterized by numerical value of 1/τ (where τ is the relaxation period). The phase portraits of all oscillation-relaxation curves are in good agreement with the Faraday law.