Insulator‐based dielectrophoretic focusing and trapping of particles in non‐Newtonian fluids

Abstract

Insulator-based dielectrophoretic (iDEP) microdevices have been limited to work with Newtonian fluids. We report an experimental study of the fluid rheological effects on iDEP focusing and trapping of polystyrene particles in polyethylene oxide, xanthan gum, and polyacrylamide solutions through a constricted microchannel. Particle focusing and trapping in the mildly viscoelastic polyethylene oxide solution are slightly weaker than in the Newtonian buffer. They are, however, significantly improved in the strongly viscoelastic and shear thinning polyacrylamide solution. These observed particle focusing behaviors exhibit a similar trend with respect to electric field, consistent with a revised theoretical analysis for iDEP focusing in non-Newtonian fluids. No apparent focusing of particles is achieved in the xanthan gum solution, though the iDEP trapping can take place under a much larger electric field than the other fluids. This is attributed to the strong shear thinning-induced influences on both the electroosmotic flow and electrokinetic/dielectrophoretic motions.

Fluid rheological effects on streaming dielectrophoresis in a post‐array microchannel

“…A complete trapping of particles occurs 80 V DC/ 420 V AC, for which the effective electric field, $${E_{eff}} = \ 2285$$ V/cm, is about 30% greater than that for the Newtonian case. These observations do not exhibit apparent deviations from those in the single‐constriction channel in our previous paper [42]. Therefore, the presence of successive contractions and expansions in the post region does not cause a different influence on the electroosmotic fluid flow (see Fig.…”

“…An interesting phenomenon worth mentioning is the quick formation of gel‐like structures in the post region under 500 V DC (Figure 4B, which also occurs under 400 V DC but at a later stage). Such a phenomenon was not observed in the single‐constriction microchannel [41,42] even when the average electric field inside the constriction (about 5000 V/cm at the highest for 500 V DC) gets much higher than that in between the posts in the current post‐array channel (about 2000 V/cm at the highest for 500 V DC). This occurrence cannot be explained by the increased action of iDEP as the manifestation varies greatly from the observations in the Newtonian and PEO cases.…”

“…Therefore, the presence of successive contractions and expansions in the post region does not cause a different influence on the electroosmotic fluid flow (see Fig. 3B) or electrokinetic particle motion from that in a single‐constriction microchannel [42] for both the Newtonian buffer and viscoelastic PEO solutions. This may indicate that the fluid elasticity alone, unless too strong [43,44], has an insignificant impact on the electroosmotic flow or electrokinetic motion.…”

“…We proposed in our previous paper [42] a revised theory for iDEP focusing and trapping of particles in non‐Newtonian fluids. Briefly, we introduced one correction factor, $${G_D}( {Wi,\ n} )$$, as a function of the Weissenberg number, $$Wi$$, and power‐law index, $$n$$, to account for the fluid elasticity and shear‐thinning effects, respectively, on the dielectrophoretic particle velocity [42], $$\begin{equation}{U_{DEP\_\hat{s}}} = \frac{{{\mu _{DEP}}}}{{{G_D}\left( {Wi,\ n} \right)}}\ \frac{{\partial {E^2}}}{{\partial \hat{s}}}\end{equation}$$ $$\begin{equation}{U_{DEP\_\hat{n}}} = \frac{{2{\mu _{DEP}}}}{{{G_D}\left( {Wi,\ n} \right)}}\ \frac{{{E^2}}}{{\cal R}}\end{equation}$$ $$\begin{equation}Wi\ = {\rm{\ }}\lambda \dot{\gamma }\end{equation}$$where $${U_{DEP\_\hat{s}}}$$ and $${U_{DEP\_\hat{n}}}$$ are the dielectrophoretic velocities ...…”

Effect of skimming layer in an electroosmotically driven viscoelastic fluid flow over charge modulated walls

“…There are several studies highlighting the flow of Newtonian fluids using the electroosmotic drive [9][10][11]. Unlike the Newtonian fluid which are governed by a linear relationship between the stress and rate of strain, the polymeric/synthetic or biofluids generally show nonlinear rheological characteristics [12][13][14][15][16]. Typically, viscoelastic constitutive relationships are employed to successfully mimic biofluid transport [17][18][19][20][21].…”