Experimental Study of Capillary-Rise Behavior and Meniscus Evolution in Glass Capillaries Under an Electric Field.

To elucidate the scale-dependent response and interfacial evolution of liquid capillary rise in glass capillaries under an electric field, capillaries with different inner diameters were used as model channels. The equilibrium capillary-rise behavior of NaCl solutions without an electric field was investigated, and the coupled effects of capillary diameter, temperature, and concentration were analyzed using response surface methodology. The additional rise of the liquid column under a direct-current electric field was examined, and the interfacial evolution mechanism was explored through meniscus visualization. The results show that, without an electric field, the equilibrium capillary height is governed mainly by capillary inner diameter, followed by temperature, whereas concentration has a relatively weak effect. The developed quadratic regression model shows high fitting accuracy. Under the applied electric field, the electrocapillary response exhibits clear scale selectivity. No significant additional rise was observed in the 0.1 mm and 0.3 mm capillaries, whereas the liquid-column height increased markedly in the 0.5 mm capillary. At 30 °C and 0.75 kV, the additional rise reached 8.2 mm, corresponding to a relative increase of 15.30%. The enhancement at 0.75 kV was stronger than that at 1.5 kV, indicating a non-monotonic voltage response. Meniscus experiments further show that 0.32% NaCl and 5% ethanol solutions respond more evidently to the electric field, with stronger interfacial restructuring for NaCl solution at 0.75 kV. These results indicate that the electric field modifies capillary pressure by altering the force balance near the three-phase contact region and the meniscus curvature, thereby inducing additional liquid-column rise.