microphases

Microphases are mesoscopic phases in which an order parameter varies periodically on length scales between molecular dimensions and macroscopic size. They arise when competing interactions favor demixing locally but are constrained globally, producing spatially modulated structures with characteristic spacings from a few to several tens of nanometers in many materials.

In polymer science, the best-studied microphases occur in block copolymers, where incompatible blocks are covalently linked. Phase separation is arrested, yielding ordered domains such as lamellae, cylinders, gyroids, or spheres. The morphology depends on the volume fraction of each block, the interaction strength, and processing conditions; the domain spacing is set by a balance of interfacial energy and chain stretching, and can be tuned by molecular weight and temperature.

Microphases also appear in surfactant systems, lipid membranes, and some magnetic or colloidal suspensions where competition between attractive and repulsive forces creates periodic patterns.

Characterization and theory: experiments use small-angle X-ray or neutron scattering and electron microscopy; theory includes weak- and strong-segregation analyses and models like the Ohta–Kawasaki framework to predict phase diagrams, morphologies, and domain sizes.

Applications: nanostructured materials, membranes, photonic crystals, and controlled-release systems. Understanding microphases informs design of self-assembled materials and requires control of composition, processing, and thermal history to minimize defects.