Penetration of Surfactant Solutions into Capillaries

Abstract

This investigation studies the processes by which water and surfactant solutions penetrate macroscopic, horizontal, hydrophilic glass capillaries. Additional investigations were conducted on some capillaries that are made hydrophobic by being silanised. A laser is shone along the capillary to illuminate the advancing meniscus, so the meniscus is seen as a dot of light, which is detected by a high-speed camera. An investigation on the effect of the presence and type of surfactant aims to reveal the processes by which penetration occurs. Dissipation in the wedge was investigated as a source of deviation from Lucas-Washburn behaviour. Three theoretical models were compared to the experimental data: (I) The Lucas-Washburn model, (II) A “Young” model and (III) Overflowing cylinder model. All these models are shown to be unable to account for the observed penetration rates. The wedge of liquid near the three-phase contact line is considered as a possible additional dissipative mechanism. Penetration of surfactant solutions into capillaries filled with oil is investigated. Due to the viscosity matching effect of this technique, viscous dissipation is constant.