A Model for the Stability of Films Stabilized by Randomly Packed Spherical Particles

Abstract

Particle stabilized thin films occur in a range of industrial applications where their properties affect the efficiency of the process concerned. However, due to their dynamic and unstable nature they are difficult to observe experimentally. As such, a tractable way of gaining insight into the fundamental aspects of this complicated system is to use computer simulations of particles at interfaces. This paper presents modeling results of the effect of nonuniform packing of spherical particles on the stability of thin liquid films. Surface Evolver was used to model cells containing up to 20 particles, randomly packed in a thin liquid film. The capillary pressure required to rupture the film for a specific combination of particle arrangement, packing density, and contact angle was identified. The data from the periodic, randomly packed models has been used to find a relationship between particle packing density, contact angle, and critical capillary pressure which is refined to a simple equation that depends on the film loading and contact angle of the particles it contains. The critical capillary pressure for film rupture obeys the same trends observed for particles in regular 2D and 3D packing arrangements. The absolute values of P*(crit), however, are consistently lower than those for regular packing. This is due to the irregular arrangement of the particles, which allows for larger areas of free film to exist, lowering the critical capillary pressure required to rupture the film.

Motion of Particles in a Monolayer Induced by Coalescing of a Bubble with a Planar Air–Water Interface

“…Leaving a region of low packing density may increase the probability of other coalescence events. 5,7,70 The results also corroborate the fact that heavily loaded froths are less mobile due to the stiffness of the bubble. 71 3.5.…”

“…That is, particles should be able to redistribute themselves on the surface in order to cover the bare region. Leaving a region of low packing density may increase the probability of other coalescence events. ,, The results also corroborate the fact that heavily loaded froths are less mobile due to the stiffness of the bubble …”

“…The presence of a particle layer around bubbles offers a number of advantages. If the bubbles are in sufficiently close proximity, the layer may act as a steric barrier which significantly inhibits bubble coalescence. − The particle layer may also increase the mechanical strength of the bubbles and gain resistance against interfacial perturbation or deformation . Hydrophobicity, shape, size, density, chemical, and mechanical properties, as well as packing density of the particles, determine the stability of bubbles and their physical properties such as deformability and mechanical strength. ,,, …”

Experimental Technique to Study the Interaction Between a Bubble and the Particle-Laden Interface

“…The liquid in the film drained out gradually and the film ruptured once it reached a critical thickness. In the presence of particles, a three phase contact line between the bubble and particle may be established leading to particles forming a bridge in the thin liquid film (Kaptay, 2004 ; Morris et al, 2011 ), which may be influenced by the hydrophobicity of the particles and the pH of the liquid phase. The bridging of the particles may result in a significant delay in bubble coalescence time.…”

Identifying the Transition Capillary Pressure of a Superhydrophobic Surface Containing Cylindrical Rods

“…The model used for these simulations is based on those previously developed for the simulation of particles in thin films. 15,16,18,19 The Surface Evolver program is used to find the minimum energy surface of a system subject to a series of userdefined constraints. As such, it is well suited to the simulation of quasi-static systems dominated by capillary forces.…”