Rod-coil multiblock copolymers: Structure and stability

The behavior of multiblock polymers with alternating stiff and flexible blocks is discussed. The copolymers are immersed in selective solvent such that the rods are likely to aggregate to gain energy. Upon aggregation micelles appear and contribute to surface energies. This process is counterbalanced by the loss (and gain) of entropy of the flexible parts, which yields eventually to a specific number of micelles connected by flexible chains. In terms of simple scaling estimates, the average aggregation number of the rods is calculated. It is shown how the aggregation and micelle number depends on the parameters, rod length, chain length, and surface energy. The number of micelles is governed by the surface energy. For large surface energies at given system size only one micelle is favored. Lower surface energies allow for more micelles. These estimates provide sensible results if they are applied to proteins whose main structural elements are a-helices (rods) and unstructured parts (flexible chains).