Particles in the liquid-gas interface

Small particles bind to liquid-gas interfaces if the contact angle is not zero. As we will see later this is of fundamental importance in applications such as flotation or the stabilization of emulsions. For simplicity we start by considering small, spherical particles. Small refers to particles for which we can neglect gravitational effects and buoyancy. Practically, this is valid for particles with diameters in the range of up to 100 pm. 

For 0 0 a particle is stable at the liquid surface (Fig. 7.4) [229], Its position in the interface is simply determined by the fact that, in equilibrium, the liquid surface is unperturbed. A planar liquid surface will also be planar with the adsorbed particle. This is easy to understand. If the liquid surface is curved, the capillary force due to surface tension would result in a force in the normal direction. In the absence of external forces, this capillary force would draw the particle to a new position, until the curvature is zero again. If the particle is significantly larger 

We can estimate the force necessary to remove the particle from the gas-liquid interface from F pa AG/R =1.1 //,N. Compared to the gravitational force, which is of the order of ICC11 N, this is strong. We conclude that under normal conditions the particle will remain in the interface. 

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