Computer Simulations of Nano-Scale Phenomena Based on the Dynamic Density Functional Theories: Applications of SUSHI in the OCTA System

Multicomponent polymeric materials such as polymer blends, polymer melts, block copolymers, and polymer solutions, often show macro and micro phase separations that generate domains of the length scales of 1-100 nm. These polymeric materials with phase-separated domains are promising candidates for functional materials in nano-technologies [1-3]. The characteristic length scales of these domain structures are much larger than atomic length scales but are still smaller than hydrodynamic length scales. For phenomena on the micro and macroscopic length scales, there are well-established simulation techniques. For example, microscopic phenomena on atomic length scales can be dealt with using particle simulation techniques such as molecular dynamics (MD) simulations. On the other hand, macroscopic hydrodynamic phenomena are simulated with the finite element method (FEM). Compared to these extreme length scales, there have been very few simulation techniques for the intermediate length scales (the so-called mesoscopic scales) where the phaseseparated domains locate. To study the phase separated domains on mesoscopic scales, very useful tools are the density functional theories (DFTs) [4-7], where the phaseseparated domains are described in terms of the density distributions of monomers and solvents. One of the important features of DFT is that it can take into account the conformational entropy of polymer chains with any molecular architectures, i.e. the monomer sequence and the branching structures. Using this DFT, one can predict the equilibrium state of polymeric systems with mesoscopic structures, which is not easily accessible by the particle simulations or the fluid dynamics simulations. Therefore the DFT plays an important role in bridging between microscopic particle simulations and macroscopic fluid dynamics simulations.