Compared to the systems which are
composed of simple atoms or molecules, the structures of polymer systems in
equilibrium are richer. The main reason is that a polymer molecule is composed
of many monomers with the same or different chemical property.
Take AB di block
co polymers as an example. Each molecule has a form AA• • •ABB• ••B where the
monomer A and B have different chemical properties. The equilibrium structures for di block co polymer, e.g., lamellar, hexagonal cylinder, bicontinuous gyroidand bcc sphere, etc., have been found for different composition of monomer B
through computation and experiments. This equilibrium structures (A-rich and
B-rich phase domain) with a length scale of 10-100 nm, is the result of
competition of two factors: the repulsion of two chemically distinct monomer A
and B, and the conformal entropy penalty. Since monomers A and B are connected
in each molecule, monomer A and B are only be separated microscopically. Thus
it is called micro separation.
