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Publication . Teixeira, Miguel; Arscott, Steve; Cox, Simon; Teixeira, Paulo

• In confined foams there exist wall Plateau borders (PBs), or menisci, where the films meet the confining substrates. • What is the shape of a PB of a given size on a surface of a given wettability (i.e., contact angle θc)? Can that surface support a foam? • This is important for firefighting foams, containers for foamy foodstuffs, etc • We solve the Young-Laplace equation with gravity for a planar film spanning a gap between two horizontal, flat substrates, to predict the shape of the PBs. • Validate results by comparing with Surface Evolver and experimental data

2017-07Conference object

Open access

Free energy calculations for rings and chains formed by dipolar hard spheres

Publication . Ronti, Michela; Rovigatti, Lorenzo; Tavares, Jose; Ivanov, Alexey O.; Kantorovichaf, Sofia S.; SCIORTINO, Francesco

We employ a method based on Monte Carlo grand-canonical simulations to precisely calculate partition functions of non-interacting chains and rings formed by dipolar hard spheres (DHS) at low temperature. The extended low temperature region offered by such cluster calculations, compared to what had been previously achieved with standard simulations, opens up the possibility of exploring a part of the DHS phase diagram which was inaccessible before. The reported results offer the unique opportunity of verifying well-established theoretical models based on the ideal gas of cluster approximation in order to clarify their range of validity. They also provide the basis for future studies in which cluster–cluster interactions will be included.

2017-11-21Journal article

Open access

When is a surface foam-phobic or foam-philic?

Publication . Teixeira, Miguel; Arscott, Steve; Cox, Simon; Teixeira, Paulo

It is commonly assumed that the liquid making up a sessile bubble completely wets the surface upon which the bubble lies. However, this need not be so, and the degree of wetting will determine how well a collection of bubbles - a foam - sticks to a surface. As a preliminary to this difficult problem, we study the shape of a single vertical soap film spanning the gap between two flat, horizontal solid substrates of given wettabilities. For this simple geometry, the Young-Laplace equation can be solved (quasi-) analytically to yield the equilibrium shapes, under gravity, of the two-dimensional Plateau borders along which the film contacts the substrates. We thus show that these Plateau borders, where most of a foam's liquid resides, can only exist if the values of the Bond number Bo and of the liquid contact angle yc lie within certain domains in (yc, Bo) space: under these conditions the substrate is foam-philic. For values outside these domains, the substrate cannot support a soap film and it is foam-phobic. In other words, on a substrate of a given wettability, only Plateau borders of a certain range of sizes can form. For given (yc, Bo), the top Plateau border can never have greater width or cross-sectional area than the bottom one. Moreover, the top Plateau border cannot exist in a steady state for contact angles above 901. Our conclusions are validated by comparison with both experimental and numerical (Surface Evolver) data. We conjecture that these results will hold, with slight modifications, for non-planar soap films and bubbles. Our results are also relevant to the motion of bubbles and foams in channels, where the friction force of the substrate on the Plateau borders plays an important role.

2018-07-14Journal article

Restricted access

Dynamics of patchy particles in and out of equilibrium

Publication . Tavares, Jose; Dias, Cristóvão; Araujo, Nuno; Gama, Margarida

We combine particle-based simulations, mean-field rate equations, and Wertheim's theory to study the dynamics of patchy particles in and out of equilibrium, at different temperatures and densities. We consider an initial random distribution of nonoverlapping three-patch particles, with no bonds, and analyze the time evolution of the breaking and bonding rates of a single bond. We find that the asymptotic (equilibrium) dynamics differs from the initial (out of equilibrium) one. These differences are expected to depend on the initial conditions, temperature, and density.

2018-04-05Journal article

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Dynamics of a network fluid within the liquid–gas coexistence region

Publication . Dias, Cristóvão; Tavares, Jose; Araujo, Nuno; Gama, Margarida

Low-density networks of molecules or colloids are formed at low temperatures when the interparticle interactions are valence limited. Prototypical examples are networks of patchy particles, where the limited valence results from highly directional pairwise interactions. We combine extensive Langevin simulations and Wertheim's theory of association to study these networks. We find a scale-free (relaxation) dynamics within the liquid–gas coexistence region, which differs from that usually observed for isotropic particles. While for isotropic particles the relaxation dynamics is driven by surface tension (coarsening), when the valence is limited, the slow relaxation proceeds through the formation of an intermediate non-equilibrium gel via a geometrical percolation transition in the Random Percolation universality class. We show that the slow dynamics is universal, being also observed outside the coexistence region at low temperatures in the single phase region.

2018-04-14Journal article

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