Calibration of acoustic radiation pressure field inside microchannels using microparticle zeta potential measurement

Abstract

We present a new method to extract acoustic radiation field inside a PZT-glass capillary microfluidic actuator, used for collection and separation of micro-nano-particles and biological entities. By focusing particles in a small volume, acoustic forces counteract against natural dispersive forces. Investigation of these dispersive forces related to zeta potential enables calculation of the acoustic force inside the complex microfluidic system. Related to the problem given above, we present a new method to estimate the acoustic field inside the capillary. It is known that acoustic radiation force on a spherical object is related to its radius (3). While radiation force decreases by the size of the particle, small particles collected inside the channel tend to disperse due to Brownian motion and electrostatic interactions of the Debye layer surrounding them. The Debye layer interaction can be quantified by measuring the zeta potential of the suspended particle. While Brownian motion will be only related to the temperature and the viscosity of the suspension, varying the pH of the solution enables control of the zeta potential around the particles. Although, zeta potential change has negligible affect on the acoustic field, it changes the electrostatic interaction between the particles depending on the value of the pH change. By, calculating the dispersion force due to the repelling of charged particles by knowing their zeta potential, the counter balancing ultrasonic force produced by the acoustic field can be estimated.