arXiv subjects

Emmanuelle Rio

Publications and source records attributed to Emmanuelle Rio.

39 records · Page 3Linked to original sources

arXiv2016

The surface tells it all: Relationship between volume and surface fraction of liquid dispersions

The properties of liquid dispersions, such as foams or emulsions, depend strongly on the volume fraction $ϕ$ of the continuous phase. Concentrating on the example of foams, we show experimentally and theoretically that $ϕ$ may be related to the fraction $ϕ_s$ of the surface at a wall which is wetted by the continuous phase - given an expression for the interfacial energy or osmotic pressure of the bulk system. Since the surface fraction $ϕ_s$ can be readly determined from optical measurement and since there are good general approximations available for interfacial energy and osmotic pressure we thus arrive at an advantageous method of estimating $ϕ$. The same relationship between $ϕ$ and $ϕ_s$ is also expected to provide a good approximation of the fraction of the bubble or drop surface which is wetted by the continuous phase. This is a parameter of great importance for the rheology and ageing of liquid dispersions.

cond-mat.soft↗

arXiv2014

Surfactant-induced rigidity of interfaces: a unified approach to free and dip-coated films

The behavior of thin liquid films is known to be strongly affected by the presence of surfactants at the interfaces. The detailed mechanism by which the latter enhance film stability is still a matter of debate, in particular concerning the influence of surface elastic effects on the hydrodynamic boundary condition at the liquid/air interfaces. In the present work, "twin" hydrodynamic models neglecting surfactant transport to the interfaces are proposed to describe the coating of films onto a solid plate (Landau-Levich-Derjaguin configuration) as well as soap film pulling (Frankel configuration). Experimental data on the entrained film thickness in both configurations can be fitted very well using a single value of the surface elasticity, which is in good agreement with independent measurements by mean of surface expansion experiments in a Langmuir through. The analysis shows how and when the soap films or dip coating experiments may be used to precisely and sensitively measure the surface elasticity of surfactant solutions.

cond-mat.soft↗

arXiv2011

Dynamical thickening transition in plate coating with concentrated surfactant solutions

We present a large range of experimental data concerning the influence of surfactants on the well-known Landau-Levich-Derjaguin experiment where a liquid film is generated by pulling a solid plate out of a bath. The thickness h of the film was measured as a function of the pulling velocity V for different kind of surfactant and at various concentrations. Measuring the thickening factor $α=h/h_{LLD}$, where hLLD is obtained for a pure liquid, in a wide range of capillary ($Ca=ηV/γ$), two regimes of constant thickening can be identified: at small capillary number, $α$ is large due to a confinement and surface elasticity (or Marangoni) effects and at large Ca, $α$ is slightly higher than unity, due to surface viscous effects. At intermediate Ca, $α$ decreases as Ca increases along a "dynamic transition". In the case of non-ionic surfactants, the dynamic transition occurs at a fixed Ca, independently of the surfactant concentration, while for ionic surfactants, the dynamic transition depends on the concentration due to the existence of an electrostatic barrier. The control of physico-chemical parameters allowed us to elucidate the nature of the dynamic transition and to relate it to surface rheology.

cond-mat.soft↗