Multiscale molecular dynamics approaches to investigate non-equilibrium phenomena of colloidal assemblies

Lead Research Organisation: Imperial College London
Department Name: Dept of Chemistry

Abstract

Multiscale non-equilibrium phenomena occur over a wide range of length and time scales, such as in nanoparticle assemblies under the influence of external fields, and are often difficult to capture using a single simulation technique. The study of nanoparticle assembly away from equilibrium is amenable to multiscale methods. In recent years, hierarchical multiscale methods have been especially successful in building large chemically specific simulations of nanoparticle self-assembly in polymer nanocomposites. The project will focus on the development and implementation of multiscale approaches, such as molecular dynamics and stochastic rotation dynamics, to compute the properties of colloidal assemblies under the influence of external fields in 2 and 3 dimensions. This problem is of interest in a wide range of areas from control of plasmonic structures to energy transport in colloidal assemblies.

Publications

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Gittus OR (2019) Thermal orientation and thermophoresis of anisotropic colloids: The role of the internal composition. in The European physical journal. E, Soft matter

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509486/1 01/10/2016 31/03/2022
2135626 Studentship EP/N509486/1 06/01/2018 31/07/2021 Oliver Gittus
 
Description Using theory and simulation, we suggest new ways in which soft matter can be manipulated with thermal fields. In particular, we have found that mass asymmetry can affect the thermal diffusion in (1) colloidal suspensions and (2) molecular mixtures.

(1) The drift motion experienced by colloids immersed in a fluid with an intrinsic temperature gradient is referred to as thermophoresis. An anisotropic mass distribution inside colloidal particles imparts a net orientation with respect to the applied thermal field, and in turn alters the thermophoretic response of the colloids. This rectification of the rotational Brownian motion is called thermal orientation. Using both theory and simulation, we found that the average orientation and the Soret coefficients of the colloids can depend significantly on the internal mass distribution. This observation suggests an approach to identify internal colloidal compositions using thermal gradients as sensing probes.

(2) Temperature gradients bring novel approaches to manipulate multi-component fluids. Observations made nearly two centuries ago by Ludwig and Soret demonstrated that temperature gradients can induce concentration gradients. It is now well established that thermal diffusion can be used to separate components based solely on their total mass and mass distribution. This isotopic Soret effect can be relatively large, and even the dominant contribution in molecular mixtures.
To date, the effect of internal mass distribution in molecular mixtures has been rationalised in terms of only the moment of inertia. We found that mixtures of rigid rod-like particles can be separated based on their mass asymmetry, introducing a new term to the empirical equations found in literature. We link this new effect primarily to a difference in the thermal diffusion coefficients. Our results suggest that the Soret coefficient can be tuned by the internal mass distribution with potential applications in the fractionation and characterisation of molecular mixtures.
Exploitation Route Experimental confirmation.
Sectors Chemicals,Energy