Wettability determined by capillary rise with pressure increase and hydrostatic effects

[Display omitted] ► We investigate the hydrostatic effects in the capillary rise. ► Derived an improved expression. ► Feasibility confirmed by high correlation coefficients and good reproducibility. ► The validity of the improved expression was confirmed. ► It becomes possible to more precisely measure the wettability of small particles. Capillary rise is the basis of some methods that are widely applied for the determination of contact angles as well as wettabilities of small particles. The equivalent hydraulic radius rd in the Classical Washburn equation is assumed to be particle-specific. But it seems that rd is not always constant when the type of liquids is different. The new equation with the pressure increment and the hydrostatic effects are theoretically derived based on the Washburn equation, so contact angles of small particles can be measured experimentally independently of rd. The result shows the validity of the proposed method, and therefore, it becomes possible to accurately measure the wettability of small particles.