Slow development of induced-charge electro-osmosis in cetyltrimethylammonium bromide solutions

Abstract

Induced-charge electro-osmosis (ICEO) is an important phenomenon in microfluidics and has been widely studied. Existing studies, both theoretical and experimental, have shown that ICEO is fully developed in milliseconds after an electric field is applied. In this study, we experimentally found that ICEO of cetyltrimethylammonium bromide (CTAB) solutions takes several seconds to be fully developed after the electric field is applied, which is significantly different from the existing literature. To reveal the underlying mechanism of this slow development, we propose a phenomenological model for ICEO of CTAB solutions by incorporating a dynamic viscosity formula. The ICEO model successfully explains the slow development and attributes it to the thixotropy of CTAB solutions. In addition, we also found that ICEO velocity varies irregularly as CTAB concentration increases, which is due to the variations of viscosity and electrical conductivity of CTAB solutions. The ICEO velocity of CTAB solutions reduces as the electric field frequency increases, which is different from the existing literature. The findings may enrich the understanding of ICEO and promote the application in complex fluids such as biological fluids.