PHD Defense - Mengshi Wei - 28/09/2022 - Active Colloidal Gels

Mengshi Wei’s PhD Defense will take place on:
September 28th at 2pm
Charpack Hall, ESPCI
10 rue Vauquelin, 75005 Paris

Active Colloidal Gels
On their way towards equilibrium, but kinetically arrested, colloidal gels form a peculiar state of matter halfway between liquids and solids. Systems of active particles that convert external energy into mechanical work have been the focus of intense research in the past 25 years, as they exhibit a number of phases of matter, which are out of reach for equilibrium systems.

In the present work, we study a system that combines colloidal gelation and activity. To do so we embed active particles whose activities are controlled by external blue light into a colloidal gel. We then investigate the response of the already-formed passive colloidal gel to activity and the effects of activation on the properties of the gels. We monitor the structure and dynamics of the gel, both before, during, and after the activation period.

During activation, the mobility of the passive particles composing the gel increases and exhibits a characteristic scale-dependent response to the activation. The gel reorganizes, with smaller strands coalescing with larger ones and leaving larger holes in the structure. Interestingly, once activation is switched off, the gel keeps the memory of the activation period.