TYC@Imperial Soiree: Modelling charged clay colloids and cohesionless sand grains

Thursday 10th May
Time: 16.00
Venue: Lecture theatre G20, Royal School of Mines, Imperial College London
Contact: Ms Hafiza Bibi
Tel: 02075947252

Molecular Dynamics and Engineering Understanding of Sand Behaviour

Prof. Catherine O’Sullivan, Prof. of Particulate Soil Mechanics, Dept. Civil and Environmental Engineering, Imperial College London

Granular materials, including sand, behave in a rather complex way. Predicting sand behaviour is essential for large infrastructure projects including dams and foundations to structures.  Significant insight into the material behaviour can be obtained by simulating these materials at the particle scale.  This talk will consider the use of discrete element method / molecular dynamics simulations to simulate sand behaviour.  The talk will present some ways in which use of this simulation strategy has measurably improved understanding and given a more scientific basis to guidelines used in engineering design.   The talk will also consider the challenges of running these simulations effectively, discussing issues around code validation, choice of input parameters, and numerical stability.


The potential of mean force: the tool to model dense colloidal systems

Dr Roland Pellenq, The MIT / CNRS / Aix-Marseille University Joint Laboratory, 

We investigated the interactions responsible for the cohesion of strongly interacting colloidal materials such as clays, cement... It is known that the swelling/cohesive properties of these materials depend both on the nature of the some counter-ions compensating their surface charge. The overall goal of this work is to determine the right level of modeling complexity required to capture the behavior of these charged colloids immersed in an electrolyte and set up the stage for modeling at the meso-scale. From the (analytical) mean-field DLVO theory to a full atomistic description, we introduce the concept of “Potential of Mean Force” as the tool to get an efficient but still realistic description between strongly interacting colloidal grains such as clay and cement hydrate nanoparticles. In particular, we introduced the Explicit Solvent Primitive Model (ESPM), in which ions are modeled as charged hard spheres and solvent molecules as soft spheres with embedded point dipoles. We showed that taking explicitly into account the solvent in such a Primitive Model description, allows a quantitative description of system’s cohesion in quantitative agreement with atomistic scale results. From ionic correlation interactions to pure electrostatics, the ESPM approach is shown to be an efficient strategy to get a truly consistent multi-scale modeling approach of complex systems.



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