Self-assembly of Crystallisable Diblock Copolymers

Results of self-assembly of polystyrene-polyethyleneoxide diblock copolymers, either in solution or in a thin film are presented. Depending on internal interactions and the interaction with the environment, the polymer could assemble differently giving rise to various patterns over many lengthscales. With the bare eye one could already appreciate the fractal-like or spherulite structure resulting from the overall crystallisation of the polymer. On a smaller scale, especially when looking at thin films, optical microscopy allowed the observation of square platelets of several micrometers. Atomic force microscopy revealed the molecular organisation within these patterns. Depending on the relative length of the blocks and crystallisation kinetics, sheets of molecular thickness containing rather regularly distributed cylindrical holes, "spider's webs', island-hole patterns, etc. were found. Tentative explanations are attempted based on the minimisation of the free energy controlled by crystallisation and entropie (steric) effects due to the fact that the two blocks of incompatible polymers are connected.