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Depletion interactions in soft particle suspensions

Microgels are responsive cross-linked colloidal particles with a polymeric network structure, which undergo solvation changes in response to the application of an external stimulus such as temperature, pH or electrolyte concentration. In this project, depletion interactions induced by the presence of a fraction of small microgel particles in a suspension of large microgels (PNIPAM cross-linked with MBA) are studied. Microgels are used as a versatile model system where the effective volume fraction and the strength and shape of the interaction potential can conveniently be changed via a change in temperature. In order to perform these studies, a combination of techniques such as 3D cross-correlation light scattering, ultra-small angle light scattering, small-angle x-ray and neutron scattering, confocal laser scanning microscopy and rheology is used. We characterize the effective interaction potential USS(r), ULL(r), and USL(r) between the particles, where the subscripts S and L stand for small and large particles, respectively, from measurements of the pair correlation functions g(r) combined with computer simulations. We then investigate the phase diagram and determine the structural and dynamic properties of the system as a function of temperature, mixing ratio and volume fractions of small and large particles.

People: Maxime Bergman, Marc Obiols-Rabasa, Emanuela Zaccarelly (University La Sapienza Rome, Italy), Peter Schurtenberger.

Contact person: Peter Schurtenberger