Wall repulsion of charged Brownian particles subjected to alternating current electric fields in microfluidic channels

This study investigates the wall repulsion of submicrometer particles (0.5 μm and 0.75 μm in diameter) under an alternating current electric field and evaluates whether this phenomenon can be explained by the wall-particle interaction due to concentration polarization electro-osmosis (CPEO), a theory previously validated for larger particles. Our findings confirm that CPEO, rather than electric repulsion, is the primary mechanism driving particle-wall repulsion. Experimental results show that the particle distribution across the channel width aligns with predictions from a one-dimensional Fokker–Planck model incorporating CPEO-induced repulsion. The repulsion strength decreases with increasing frequency and electrolyte conductivity, which is consistent with the CPEO theory. This work enhances the understanding of CPEO-driven particle repulsion from walls in the Brownian regime, offering valuable insights for microfluidic applications involving submicrometer particles.