Bicontinuous phases domain morphology

Asymmetric block copolymers which form hexagonal or cubic-packed spherical morphologies in the bulk, form stripe or circular domain patterns in two dimensions, as illustrated in Figure 5. The stripe pattern results from cylinders lying parallel to the substrate, and a circular domain surface pattern occurs when cylinders are oriented perpendicular to the substrate, or for spheres at the surface. Bicontinuous structures cannot exist in two dimensions therefore the gy-roid phase is suppressed in thin films. More complex multiple stripe and multiple circular domain structures can be formed at the surface of ABC triblocks (83). Nanostructures in block copolymer films can be oriented using electric fields (if the difference in dielectric permittivity is sufficient), which will be important in applications where parallel stripe (84) or perpendicular cylinder configurations (85) are desired. 

Other more complex morphologies also arise for A-B mixtures. In particular, domains A and B may enclose each other, forming entangled networks, separated by a hyperbolic interface. Those cases include mesh , bicontinuous microemulsions, bicontinuous cubic phases and their disordered counterparts, sponge phases, which are discussed below. In these cases too, the sign (convex/concave) of the interfacial mean curvature sets the Type . A representation of the disordered mesostructure in a Type 2 bicontinuous microemulsion is shown in Figure 16.3. A hyperbolic interface may be equally concave and convex (a minimal surface, e.g. see Figure 16.2(c)) so that the mesophase is neither Type 1 nor Type 2. Lamellar mesophases ( smectics or neat phases) are the simplest examples. Bicontinuous balanced microemulsions, with equal polar and apolar volume fractions are further examples. 

Figure 16.17. Bilayer morphologies of a bicontinuous mesophase (P) of Types 1 and 2. (a) Type 1 bicontinuous mesophases consist of a reversed, polar (e.g. water-filled) film (thickness 2t ) folded on to the P surface, immersed in two disconnected but interwoven apolar (paraffin) continua, with one on either side of the surface, (b) Type 2 phases contain a paraffin film of thickness twice the chain length, 2/, separating polar domains...

---