Fractionation of multiscale particle mixtures using acoustic field-flow fractionation with steric and normal mode combination

Abstract

An acoustic field-flow fractionation (FFF) system was developed to fractionate particle mixtures with a wide size distribution by combining steric and normal mode mechanisms. The system utilized piezoelectric transducers on the top surface of the channel to generate a stable quarter-wavelength standing wave in the carrier liquid flow, controlled by the sinusoidal voltage amplitude. The acoustic radiation force from the ultrasonic standing wave suppressed Brownian diffusion, allowing for the vertical equilibrium distribution of Brownian-diffusive particles to be confined. This enabled their transport and elution by the carrier liquid velocity at the centroid of their distribution without impacting non-diffusive particles. Experimental results showed that the acoustic radiation force generated by the established standing acoustic wave field, which increases with applied voltage, effectively inhibited Brownian diffusion of 1.0 & micro;m particles at an applied voltage of 20 Vpp, thereby directing their transport according to the steric mode. Additionally, successful fractionation of a particle mixture comprising particles with radii of 350 nm, 550 nm, 1.0 & micro;m, 2.5 & micro;m, and 5.0 & micro;m demonstrated that the acoustic FFF system could separate particles across a wide size range using a hybrid separation mode that combines steric and normal modes. Theoretical predictions suggested that at an applied voltage of 80 Vpp, the acoustic FFF channel could extend the normal mode fractionation to particles below 45 nm, facilitating the separation of multiscale particle mixtures without the need for preprocessing.