In this case, we have a thin film (~50nm) of polystyrene that has been deposited atop a thicker film (~130 nm) of poly(methyl methacrylate), where the two polymers are completely immiscible. This so-called PS/PMMA bilayer film is itself deposited on a silicon wafer. When the system is heated above the glass transition point of the constituent polymers (~100oC for PS and PMMA), the polymer molecules will move to minimize the total energy of the system. PS will bead up on a PMMA surface in much the same way that water does on wax, but is much slower (and therefore easier to study!) Due to the very high viscosity of polymers in their rubbery melt state. Shown in this image is the final pattern seen when a PS film has completely “beaded up” on a PMMA substrate. The white circular areas are the remnants of the PS film while the blue area is the still intact PMMA substrate. One can clearly distinguish a cellular pattern, where the cell centers correspond to the centers of the original holes as the PS film was breaking up.