Simulation study of spiral spinodal decomposition in polymer mixtures.

A film of a binary polymer mixture between two concentric cylindrical walls is studied numerically with the help of diffuse-interface modeling. The system starts with a homogeneous temperature above the upper critical value Tc, while the inner cylinder is cooled below Tc. The outer wall has a low, negligible heat conductivity. Around the inner cylinder, the system cools down and spinodal decomposition sets in. Starting from a non-radially symmetric pattern at the inner cylinder, domains of coexisting mole fractions emerge. At later times, one of the following structures forms: (a) a set of nested rings or (b) spirals growing from the inside to the outside. The spiral shape is of particular nanotechnological interest, since it allows the creation of a long continuous path from the inside to the outside. If one of the domains is electrically conductive, a flat spiral coil can be created. By crosslinking one component and removing the other, a spiral, percolating path can be formed through the solid component. The large surface area of the spiral path can be used for cooling a fluid running through it or for catalytic applications.