Laboratoire Matière et Systèmes Complexes

Chargée de recherche - CNRS

berengere.abou(at)univ-paris-diderot.fr

Bâtiment Condorcet, Bureau 712A (76257), Labo 590A (76161)

Supervisor : Bérengère Abou

berengere.abou(at)univ-paris-diderot.fr

Dense colloidal suspensions are model systems to mimic the glass transition. With increasing volume fraction, they can form liquids, crystals, and glasses at the highest volume fractions. This colloidal glass transition is analogous to the glass transition in liquids, with colloids playing the role of atoms. Because the colloidal particles are much larger, these systems provide slower (thus accessible) time scales than in atomic glasses, and the possibility to be probed with simple optical techniques such as microscopy and dynamic light scattering.

Glasses exhibit heterogeneous dynamics characterized by fast and slow domains coexisting in the sample (Figure : fast (red) and slow (blue) domains coexisting in dense soft thermosensitive colloids.). A key point in understanding the glass transition scenario concerns these dynamic heterogeneities and their evolution (length scale) when approaching the glass transition. We will work with soft thermosensitive microgels (100 nm -1 µm) as colloids. A unique advantage of the microgels is that their radius depends on temperature in a range close to the ambient 20-30°C. The suspension volume fraction can then be reversibly tuned with temperature, which provides a unique way to explore the phase behavior (liquid, glass) on the same sample.

During this internship, we will investigate the dynamic heterogeneities with (i) particle tracking (ii) image correlation analysis. We will investigate suspensions with various microgels softness. This parameter is of great interest since it monitors the intensity and time of the sample relaxation after a quench in temperature (when stresses generated through the sample relax with time). The candidate will benefit from excellent collaborations with the theoretical group in the institute, and collaboration with the industrial group Solvay (COMPASS, USA).

R. Colin, Ahmed M. Alsayed, J.-C. Castaing, R. Goyal, L. Hough & B. Abou, Spatially heterogeneous dynamics in a thermosensitive soft suspension before and after the glass transition, Soft Matter, 7 4504 (2011).

Experimental techniques : particle tracking, image correlation, passive and active (magnetic) microrheology, dynamic light scattering, image analysis