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Insertion of colloidal particles in the bulk and at the interface of complex fluids

Mixed systems composed of colloidal (either micro or nano) particles inserted in liquid crystal matrix are expected to give birth to very exciting new properties, especially in the field of metamaterials. On top of this, important fundamental questions are still to be answered in this type of systems (geometry of distortions, particle interactions, topological defects, etc.).

We recently showed that the shape of colloidal particles is of tremendous importance when considering the distortion energy induced by a particle embedded in a nematic liquid crystal fluid (Mondiot et al., PRL 2009). These results thus prove that new original routes can be explored in order to build new mixed materials composed of homogeneously dispersed micrometric particles in nematic liquid crystals. Indeed, playing with the particle shape allows for the tuning of the particles interactions in an anisotropic matrix.

We now wish to extend these first findings in the following directions :

-  How do the distortions induced by the particles change when approaching phase transitions ? Can elastic interactions exist inside isotropic phases in the vicinity of a phase transition line ? These questions are reminiscent of previous theoretical predictions (Galatola et al. PRE 2003, Lammert et al. PRE 1995) which have been partially confirmed by recent experiments from Abbott and coworkers (Langmuir 2009) who showed that particles can generate a pre-ordering at their surface when approaching the transition line.
-  The distortion energy induced by the particles also depends on their size. It was thus recently shown that nanoparticles inserted in a nematic fluid trigger long range interaction which are totally reversible. Thus, new thermodynamically stable phases made of particles inserted in liquid crystals can be expected. The number of expected structures is very large and potential applications of such systems are very exciting.
-  The presence of micrometric particles at a liquid crystal/air interface also generates some surprising configurations of the meniscus close to the particle. Recent experiments performed in our laboratory revealed a patterning of the interface that is strongly dependent on the liquid crystal structure. A full understanding of these first results is not achieved yet and many additional experiments are still to be performed.

The recruited PhD student will have to develop an experimental work on these different approaches. The subject is meant to be very wide but the candidate may focus on one particular point depending on the advancement of our knowledge at the beginning and during the course of the PhD.