Microrheology of dense colloidal suspensions

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We have been awarded an International Exchanges Grant by The Royal Society (IES\R1\191066) to start a research collaboration with Prof Antonio Puertas, from the Department of Physics and Chemistry at the University of Almería (Spain).

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Many products we use and enjoy every day, from paints to milk, are made by very small particles dispersed in a medium and are referred to as colloids. Colloids are widely employed in pharmaceutical, cosmetic and personal care formulations. Understanding how colloid-based formulated products respond to external stimuli is especially relevant to assess their performance in practical situations. For instance, a paint should flow easily when applied, but stay adhered to the substrate as it dries out. A toothpaste is expected to flow like a liquid only when its tube is squeezed. Controlling the behaviour of a colloid out of its equilibrium conditions is therefore crucial to exploit its properties and make a successful formulation out of it. The time-dependent behaviour of colloids under the influence of external forces (a branch of science called rheology) can be assessed by simulations. However, the standard simulation techniques are computationally very demanding, limiting their use for practical applications. Even more, if the hydrodynamic interaction is modeled, the dispersing medium must be explicitly considered. By pooling of skills, this project aims to merge together two simulation techniques that can unveil the rheology of colloids more efficiently. Specifically, we will apply Dynamic Monte Carlo simulations (Manchester expertise), which do not require the explicit description of the solvent nor the calculation of particle forces and velocities, to infer the rheology of a colloidal suspension by studying the dynamics of a guest tracer diffusing through it, referred to as microrheology (Almeria expertise).

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