Detachment of small axisymmetric particles from fluid-liquid interfaces

Abstract

Free-energy and force analyses neglecting gravitational effects were developed to predict the equilibrium position of smooth particles of any axisymmetric shape undergoing compressive or tensile forces at fluid-liquid interfaces. The force required to pull a particle from a liquid interface defined by a perforated plate was shown to be a function of the interfacial tensions, the shape of the particle and the particle/plate gap. Predictions are also given of the force at the point of particle detachment and the distance at which this process takes place. Implicit analytical expressions are provided for a conical punch or for spherical and spheroidal particles, and force-displacement diagrams are discussed. The free-energy and the force analyses are numerically equivalent, provided Young's equation is valid. The new framework provides a method to measure the contact angle properties of small particles, and the interfacial tension of the fluid-liquid interface in contact with the particle. This technique is potentially interesting in the field of bioadhesion, since it furnishes a direct method to test the adhesion of a particle to a biological substrate.