Projet ANR-07-BLAN-0243 – SURFOIDS : Colloids at tailored interfaces: design, behaviour and processing
Programme : Blanc (BLANC) 2007
Année de financement : 2007
Coordinateur du projet : CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE LANGUEDOC-ROUSSILLON (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE LANGUEDOC-ROUSSILLON)
Partenaires : Centre national de la recherche scientifique; Centre national de la recherche scientifique
Montant : 220000.0 euros
Date de début : 2007
Durée : 36 mois
Résumé : The aim of the project is to study the behaviour of micrometric particles trapped on fluid fluid interfaces by combining engineering of the systems at the microscopic level with physical understanding of the macroscopic behaviour. -  The first step of the project concerns one single particle at an interface. We will first observe the deflection of the liquid interface around a single particle, whose size, shape and surface composition will be properly controlled. Optical tweezers-aided interferometric methods will be set up to this aim. An original aspect of the project resides in the fact that we will not only prepare various types of particles, but we will also try to tailor the structure of the supporting liquid phase, using liquid crystals suitably cast as to induce interesting elastic coupling. In that case the equilibrium distortion of the interface induced by the presence of the particle will result from a compromise between capillary and elastic forces. Predictive models for the interface deflection will be developed, based on generalized Laplace equation for soft matter interface. -  Taking the opposite point of view, we will determine where a single particle preferentially sits on a complex interface of inhomogeneous curvature. Inhomogeneously curved interface will be obtained in several ways, either by perturbing the interface of an isotropic liquid by dipping macroscopic objects or using liquid droplets supported on micro-patterned substrates. Taking advantage of defects in liquid crystals we also know how to create a curvature modulated interface. Using again multitraps laser tweezers we will topographically characterize the force field the particle is submitted to. The capillary force which solely depends on the gradient of Gaussian curvature will be expressed by generalizing a multipolar expansion method to adapt to the present particular situation of a freely adjustable contact line. This necessary first step will support the following studies of the collective behaviour of particles at interface. -  When the areas of interface distortion overlap, particles interact. The perturbation of the force field in a vicinity of a second particle will be characterized. Owing to the large energy of interaction (>kT), we expect to encounter many situation of frozen equilibrium as surface fraction increases. Using magnetic particles we might be able to control the effective temperature of the system and to carry out some annealing. However kinetic aspects will be relevant in most cases and aggregation patterns resulting from different force fields will be characterized. Epitaxial growth a two-dimensional particles crystal on top of a liquid crystal is an appealing challenge, which would offer the opportunity to address interesting phenomena in 2D physics such as crystallization and melting. Finally, taking again the opposite point of view, we will explore to what extent the presence of particles at interface makes possible the shape of liquid droplets, either isotropic or crystalline, to be controlled. -  The project is carried by experimental physicists acquainted with optical methods of investigations. Collaboration includes theoreticians as well as chemists and physical chemists. Modern methods of particle synthesis or surface micropatterning we want to set up, will greatly benefit of this collaboration. ANR support is mainly asked for the optical tweezers setup and for a two years post-doc sponsorship. -                                                                                                                                                                                                                                                                            ...