[P1-80] Dynamics of Polymer Under Shear in Confinement Geometry
In lubricants, a small amount of polymer named viscosity index improver (VII) is used to control temperature dependence of viscosity. When VII is confined in small space, such as space between piston ring and cylinder bore in combustion engine, the dynamics of the solution changes due to the confinement. Here we simulate the dynamics of polymer under shear flow in confinement geometry. Polymer segment is modeled as sphere Brownian particle. The motion of the particle is tracked by the Langevin equation, whereas the Navier-Stokes equation governing the behavior of the base oil is analyzed by using the lattice Boltzmann method. The two equations are coupled through the friction between the particle and the fluid. The friction force is in proportion to the velocity of a particle relative to the host fluid, which is evaluated locally based on the velocity difference at the position of the point particle. The friction force acting on a particle is estimated by fitting the analytical solution or the flow around a Stokes-let to the flow field obtained numerically. The reaction force acts on the position of the particle, which realizes two-way coupling between the particle and fluid motions. The lattice Boltzmann method is employed for the flow simulation, which is compatible with massive parallel computing, and is easy to apply various types of boundary conditions. In order to describe confined system, periodical boundary is adopted in x, y (flow and transverse) direction, and non-slip boundary is adopted in bottom plate in z direction and moving wall is set in top plate of it. During the simulation, the polymer is pulled to upper layer where the shear field is large. To show the orientation of the molecule, order parameter is calculated. The orientation of the polymers changed to the direction of the external shear force.