Electro-osmotic flow of surfactant assisted zeta potential tuned silica frits

Abstract

The zeta potential of silica particles depends on the surface area, curvature effect, and protonation/deprotonation of surface hydroxyl groups. The electro-osmotic flux of the electro-osmotic pump (EOP) is highly dependent on the zeta potential of the silica frit. Herein, we have observed that the type of surfactant has a pronounced effect on the surface morphology, aggregation, and zeta potential of silica particles. Four different surfactants were used under identical experimental conditions. The concentration of the surfactants was well above their critical micelle concentration (CMC). The particle size, size distribution, and volume to surface mean ratio were experimentally evaluated in detail and correlated with the measured zeta potential. All the studied silica particles were highly crystalline with α-cristobalite planes. Out of the four studied silica particles, i.e., AOT–SiO₂, SLS–SiO₂, DBS–SiO₂, and HPC–SiO₂, AOT–SiO₂ showed the best results with narrow size distribution and a low volume to surface mean ratio. It has a zeta potential of −47.2 mV. We have assembled a sandwich type electro-osmotic pump and tested its performance. The best flux of 62.0 μL min⁻¹ was obtained for a frit with AOT–SiO₂ at 5 V constant applied voltage and stability of ∼5 h in a continuous run. The results demonstrated that the zeta potential of the silica particles can be tuned by an appropriate choice of surfactant for their different applications and utility.