Thermodynamics, Statistical Mechanics and Molecular Simulations

Thermodynamics, Statistical Mechanics and Molecular Simulations

Over the past couple of decades, there has been increasing focus in the chemical engineering community towards connecting material properties measured at the macroscopic level with the intermolecular interactions of the constituent molecules.

A variety of developments such as faster computers, realistic force-fields and sophisticated algorithms, have spurred the use of statistical mechanics and molecular simulations towards such research. The Supercomputer Education and Research Centre (SERC) at IISc houses the CRAY XC40 which provides a 1 petaflop computing facility serving the entire campus community. In our department, faculty have been using these tools for research in a wide variety of areas.

Atomistic molecular dynamics simulations of the lamellar phase are used to extract structural and mechanical properties which are input into large scale Lattice Boltzmann simulations to unravel the rheology of these complex mesoscale systems and connect macroscopic rheology with molecular constituents. Ayappa and co-workers have used atomistic as well as coarse grained molecular dynamics simulations to study the interaction of pore forming toxins with lipid bilayers. Micro-second long atomistic simulations of systems with over half a million atoms have been used to reveal interactions of proteins with membrane cholesterol, stability of partially formed oligomers, dynamics of lipid molecules and mechanical properties of membranes.

Punnathanam and Ayappa Labs have examined the role of organic functional groups in microporous carbons towards enhancing (i) adsorption of methane for gas storage and (ii) adsorption selectivity of carbon-dioxide from flue gases for carbon-capture and sequestration applications. Punnathanam and co-workers have performed extensive simulations of gas hydrates and have developed an improved and thermodynamically consistent theory for clathrate hydrates. Crystal nucleation is a complex phenomena which is very hard to probe experimentally. The Punnathanam group have studied crystal nucleation in hard sphere mixtures and elucidated the non-classical mechanism involved during phase transformation from a fluid phase to a crystalline phase. The Punnathanam group have also developed new simulation techniques for (i) simulation of electric double layer capacitors and (ii) calculation of free-energies of crystalline molecular solids. Understanding phenomena at the molecular scale allows one to tailor products using a bottom-up approach. Multiscale modelling strategies which bridge molecular level information with continuum transport models to study rheology of complex fluids that are ubiquitous in the beauty care industry are being pursued in the Kumaran laboratory.

Complex Fluids and Transport Processes

Complex Fluids and Transport Processes

From grains and processed foods, hygiene and cosmetic goods, and industrial products such as paints and slurries, complex fluids are widely encountered in our daily lives, in nature, and in industry. Despite their ubiquity, understanding of the flow and deformation of these materials is far from satisfactory, as their mechanics and statistics at the microscale are complex and not well understood.

Granular or particulate flows is a strong area of focus in our department, with studies ranging from stress distributions in static assemblies, through dense slow flows, to rapid inertial flows. The methods of analyses include particle dynamics simulations, continuum models based on plasticity and kinetic theory, and rheometry and flow imaging experiments. Several novel results have emerged from our department. Recent research from the Nott laboratory illustrate the presence of an anomalous stress distribution caused by a secondary flow in a cylindrical Couette device, and Kumaran and co-workers show the presence of an order-disorder transition due to base roughness in a rapid granular flow down an inclined plane. We have proposed continuum higher-gradient theories for slow and rapid flows to explain features that are not captured by the classical theories. We have recently determined by particle simulations the lift force on an object dragged through a granular medium, which has helped identify the origin of the lift.