With ever increasing computing power, one can envisage developing novel materials in-silico through bottom-up design, where chemical specificity and molecular self-assembly is used as a fabrication tool. To model these processes, we have to simulate the behaviour of the materials at the mesoscale. Modelling the very small length and timescales (atomistic) and the very large (continuum) is commonplace, but the intermediate regime (0.01—100 micrometers), where collective behaviour becomes important, is much rarer, due to the complexity resulting from interactions occurring over many length and time scales. We present examples from simulations of clay-polymer nanocomposites. Nano-composites are defined as multiphase solid materials where one of the phases has at least one dimension of less than 100 nanometres (nm) and their large scale properties are critically dependent on how the components interact on the molecular level. Clay minerals are two-dimensional sheets, with diameters of the order microns, with separation between the sheets of order nanometers. To simulate the collective behaviour of clay minerals, we need to sample both the long (microns) and short (nm) length scales. Here we will present our findings from modelling chemically specific combinations of clay, polymers and organic surfactants. We use our multiscale methods and tools to take us from a parameter free quantum description to atomistic and coarse-grained molecular dynamics simulations, thereby leading to predictions of the materials properties of these nanocomposites. Our simulations approach realistic sizes of clay platelets (currently of diameter 100-200 Å) at low clay volume fractions (5%). These systems exhibit substantial property enhancements when compared to the pristine polymer (elastic properties, gas permeation), but homogeneous dispersion of the clay sheets is required. We have used our multiscale approach to predict the melt intercalation behaviour and final morphologies of organo-treated montorillonite clay– polyvinyl-alcohol and polyethylene-glycol systems. From our multiscale simulations, we can observe the dispersion of the clay sheets, and compute various characteristics of these nanocomposites, including clay-layer spacings, out-of-plane clay sheet bending energies, X-ray diffractograms and materials properties, which we relate to the system's final morphology.

Computer-based design of advanced materials: Chemically specific multiscale modelling of polymer-clay nanocomposites

253rd National Meeting (2017)

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