Self-assembling block copolymer systems involving competing length scales: A route toward responsive materials

The phase behavior of block copolymers melts involving competing length scales, i.e., able to microphase separate on two different length scales, is theoretically investigated using a self-consistent field approach. The specific block copolymers studied consist of a linear A-block linked to an alternating (A-alt-B)-block. The large length scale microphase separation is closely related to the overall length scale of the block copolymer, whereas the short length scale microphase separation is associated with the length scale of the repeat unit of the alternating block. Because of the presence of competing intrinsic length scales, the periodicity of the lamellar structure is extremely temperature sensitive. For a range of polymer compositions a first-order phase transition occurs from a lamellar morphology with a large periodicity to a lamellar or hexagonal morphology with a much smaller periodicity. Such phase transitions could potentially form the basis for responsive materials.