Multiscale simulations of fluid flows in nanomaterials

The project will be concerned with the development of multiscale modeling techniques for simulations of fluid flows in nanomaterials. Computer simulations can provide insight into such systems when they can access, both, the atomistic length scales associated with size of the nanoparticles and the micro/macro scales characteristic of the fluid flow field. Simulations using molecular dynamics can capture the atomistic details of the nanoparticle- liquid interface but due to their computational cost they cannot be extended currently to the macroscale regime of the full flow field. In turn, continuum descriptions, using the Navier- Stokes equations may capture the macro-scale behavior of the fluid flow but they fail to represent accurately the flow field at the nanoparticle surface. The multiscale approaches, on the other hand, combine the powerful features of the both descriptions, i.e., the ability to describe the macro-scale behavior of the flow as well as accurate boundary conditions around nanoparticles. Another issue to consider when studying these systems is that typical experimental setups for molecular systems are coupled to the external environment, that is, the system is open and exchanges mass, momentum, and energy with its surroundings. Instead, standard molecular simulations are mostly performed using periodic boundary conditions with a constant number of molecules. Therefore, it is essential to develop open simulation methodologies, which, contrary to standard techniques, open up the boundaries of a molecular system and allow for exchange of energy and matter with the environment, in and out of equilibrium. The aim of the project is to combine diverse simulation techniques that separately model effectively either atomistic, mesoscale, or continuum scales of nanomaterials in a unifed multiscale framework. We will conduct multiscale simulations of the water flow through carbon-nanotubes membranes and the flow of several organic solvents, such as liquid butane, hexane, decane, and benzene, past thiolated golden nanoparticles. To this end, we will develop and employ an open molecular dynamics technique, which will enable us to perform equilibrium molecular dynamics simulations in the grand-canonical ensemble, exchanging particles with the surrounding, as well as nonequilibrium fluid flow simulations. The flow will be introduced via an external boundary condition while the equations of motion for the bulk will remain unaltered. Using this methodology we will also study the rotational and tumbling dynamics of the melt of star polymers under shear flow. Furthermore, in this project, we will study the conformational changes of proteins exposed to the shear flow. Our open multiscale approaches will bridge the hydrodynamics from the atomic to mesoscopic scale and enable the study of physical phenomena that are beyond the scope of either atomistic or mesoscopic simulations.