The determination of contact angle on porous colloid particles by wicking technique is studied.With commercial porous thin-layer silicagel plate for TLC analysis as model system,it is found that the observed differenc...The determination of contact angle on porous colloid particles by wicking technique is studied.With commercial porous thin-layer silicagel plate for TLC analysis as model system,it is found that the observed difference between liquid penetration velocity in bare and pre-contacted silicagel plates in wicking with n-alkanes is caused by capillary condensation occurred during pre-contacting process instead of dynamic contact angle.Thus only the capillary condensation effect is independently corrected,the contact angle can be obtained by wicking technique.For this purpose a new model describing the wicking in porous thin-layer plates prepared from particles with sub-pores is proposed and the corresponding wicking equations are established by introducing a parameter,tortuosity,which can be calculated independently from adsorption of the wicking liquid vapor on the thin-layer plate,into the typical Washburn equation to correct the capillary condensation effect.Applied to commercial thin-layer silicagel plates,it is found that on both bare and pre-contacted silicagel plates n-alkanes show zero contact angles,while 1-bromonaphthalene,ethylene glycol,diiodomethane,formamide and water show non-zero contact angles.The difference between dynamic advancing and receding angles is found to be very small and their average conld be taken as the equilibrium or Young’s contact angle.With this approximation the measured contact angles of 1-bromonaphthalene and diiodomethane on the silicagel plate are 20.4° and 37.2° respectively,quite in good agreement with that reported in literature.展开更多
文摘The determination of contact angle on porous colloid particles by wicking technique is studied.With commercial porous thin-layer silicagel plate for TLC analysis as model system,it is found that the observed difference between liquid penetration velocity in bare and pre-contacted silicagel plates in wicking with n-alkanes is caused by capillary condensation occurred during pre-contacting process instead of dynamic contact angle.Thus only the capillary condensation effect is independently corrected,the contact angle can be obtained by wicking technique.For this purpose a new model describing the wicking in porous thin-layer plates prepared from particles with sub-pores is proposed and the corresponding wicking equations are established by introducing a parameter,tortuosity,which can be calculated independently from adsorption of the wicking liquid vapor on the thin-layer plate,into the typical Washburn equation to correct the capillary condensation effect.Applied to commercial thin-layer silicagel plates,it is found that on both bare and pre-contacted silicagel plates n-alkanes show zero contact angles,while 1-bromonaphthalene,ethylene glycol,diiodomethane,formamide and water show non-zero contact angles.The difference between dynamic advancing and receding angles is found to be very small and their average conld be taken as the equilibrium or Young’s contact angle.With this approximation the measured contact angles of 1-bromonaphthalene and diiodomethane on the silicagel plate are 20.4° and 37.2° respectively,quite in good agreement with that reported in literature.
