Nanoparticle-Wall interactions for Implementation into Multi-scale MD-Continuum Simulations

A coupled atomistic-continuum scheme for simulating multi-scale (micro- and nano-) fluidic systems has been further developed using state exchange approach. The coupling process involves three regions i.e. continuum, atomistic and an overlap hybrid region to connect two descriptions. The coupling is applied to Lennard-Jones systems involving fluid-solid and/or fluid-fluid interfaces and the results are validated by comparing with available analytical solution. The applicability is further examined in simulating a more complex system involving liquid water. Also the interaction of a Fullerene, with a polymeric wall and a solvent, is investigated using advanced free energy calculations method. The physical behavior of the fullerene is captured through replacing it by a colloidal nanoparticle which would allow one to vary the fullerene size while modelling it as spherical particle and study its free energy and interaction forces. The results show that the solvation forces caused by fluid layers formed near the wall cause an oscillatory force on the particle which is not negligible. This work is the ground work to obtain a detailed force analysis on the nanoparticle, which will subsequently be substituted by a bio-molecule, for two purposes. One is the development of hierarchical models of bio-molecule interaction with walls of various materials used in bio-analytical devices. These hierarchical models will then be introduced into continuum models of transport in such devices. The second purpose is to incorporate the methodology to the developed hybrid MD-continuum simulation framework, which simultaneous bridges molecular-level scales to continuum scales, so as to address the physically meaningful transition of the particle (bio-molecule) from the continuum domain to the atomistic near wall domain (and vice versa) as well as it’s interaction with the wall