Structure and thermodynamics of droplets with end-grafted polymer-chains of Pickering emulsions from Molecular Dynamics Simulations and Scaling-Theory

Abstract

We consider a Pickering emulsion (oil-in-water or water-in-oil types) formed by a low-density assembly of droplets (dispersed phase) with end-grafted polymer-chains, which are dispersed in another liquid (continuous phase). The role of the added polymer is to stabilize the emulsion due the excluded volume forces between monomers. Initially, the polymer-chains are anchored onto the droplets surfaces via big amphiphile molecules and then float in the continuous phase (good solvent). As demonstrated very recently, the hairy-droplets interact mutually through an effective pair-potential which is the sum of a steric repulsive part coming from the repulsion between monomers and a van der Waals attractive one. Such a potential depends on the interdistance between adjacent hairy-droplets, their size, the bath temperature, the Hamaker’s constant, the number of grafted-polymer-chains per droplet (or equivalently the grafting-density) and their molecular-weight. The goal of this work is an extensive study of the structural and thermodynamical properties of the dispersion, using Molecular Dynamics Simulations (MDS). We note that for our study, the varied pertinent parameter is the grafting-density keeping fixed the other parameters of the problem. First , we investigate the structure of the dispersed hairy-droplets through the computation of the radial distribution function (RDF), using MDS. Second , we introduce a Scaling-Theory to investigate the hairy-droplets aggregation. The latter approach allows the determination of the fractal dimension of the hairy-droplets aggregates. Third , from the computed RDF, we extract all the thermodynamical quantities which are the virial-pressure, the internal-energy and the isothermal-compressibility. We note that our results from MSD agree well with the theoretical predictions we have deduced from Statistical Mechanics Principles. Finally, a possible link of our simulations to experiment is also discussed. • Systematic study of structure of Pickering emulsions from Molecular Dynamics Simulations. • Investigation of thermal properties of Pickering emulsions from Molecular Dynamics Simulations. • Elaboration of a scaling-theory for aggregation study. • Rigorous results from Statistical Mechanics. • Role of the grafting-density of anchored polymer-chains onto interface between dispersed and continuous phases.