Enhancement of electrokinetically driven microfluidic T‐mixer using frequency modulated electric field and channel geometry effects

Abstract

This study reports improved electrokinetically driven microfluidic T-mixers to enhance their mixing efficiency. Enhancement of electrokinetic microfluidic T-mixers is achieved using (i) an active approach of utilizing a pulsating EOF, and (ii) a passive approach of using the channel geometry effect with patterned blocks. PDMS-based electrokinetic T-mixers of different designs were fabricated. Experimental measurements were carried out using Rhodamine B to examine the mixing performance and the micro-particle image velocimetry technique to characterize the electrokinetic flow velocity field. Scaling analysis provides an effective frequency range of applied AC electric field. Results show that for a T-mixer of 10 mm mixing length, utilizing frequency modulated electric field and channel geometry effects can increase the mixing efficiency from 50 to 90%. In addition, numerical simulations were performed to analyze the mixing process in the electrokinetic T-mixers with various designs. The simulation results were compared with the experimental data, and reasonable agreement was found.

Nonlinear Smoluchowski velocity for electroosmosis of Power‐law fluids over a surface with arbitrary zeta potentials

“…In Xuan and Li's work [9], the electroosmotic flows were analyzed for microchannels with arbitrary crosssection and heterogeneous potentials. In addition, numerical simulations of the electroosmotic flow in complex geometry of microchannel networks were reported in [10][11][12][13].…”

Mixing enhancement in microfluidic channel with a constriction under periodic electro-osmotic flow

“…Coleman et al 13 proposed sequential injection of two fluids by alternate switching of electric field with an expansion chamber to enhance mixing. Yan et al 14 osmosis and pattern blocks. These active mixing methods with time periodic driving force generally require careful selection of driving frequency and oscillation amplitude for optimum mixing efficiency.…”

Optimal Frequency for Microfluidic Mixing across a Fluid Interface

“…Diffusive time-and length scales for good mixing are also usually impractical, leading to considerable interest in devising strategies to optimize mixing. Active (energysupplying) techniques used range from mechanical pulsation of fluids or device [1][2][3][4][5], electroosmotic forces [6][7][8][9][10][11], electrorheological control fluids [12], other electrokinetic forces [13][14][15][16], magnetic forces or beads [17][18][19][20], and acoustic vibration [21][22][23]. Many experimental [1,[3][4][5]7,[10][11][12][13][14][15]18,[20][21][22][23], numerical [2,4,5,8,10,11,13,15,[18]…”

“…A common theme in recent experimental and numerical investigations is to time-periodically vary the force or velocity in the active strategy used (i.e., electrokinetic forcing, magnetic force field, pulsating fluid at inlet) [1][2][3][4][5][7][8][9][10][11][12][13][14][15][17][18][19][20][21][22][23]26,28]. While ac currents are a practical reason for this, a likely motivation is the concept of chaotic mixing [29].…”

“…This provides a tool to find the optimal frequency for a given flow geometry by numerically investigating the Fourier transform of ðtÞ [48]. Frequencies which either maximize or minimize the flux can also be shown to obey the fact that Ãð!Þ and Äð!Þ ¼ F ftðtÞg lie on the same two-sided ray through the origin in the complex plane [49], that is arg½Ãð!Þ ¼ arg½Äð!Þ þ n; n an integer: (6) An electromagnetic example.-To replicate the common ''T-mixer'' inlet geometry [1,7,10,11,15], and to provide an easy illustrative situation, consider Hðx; yÞ ¼ axðL À xÞy. The flow is…”