Weak Segregation Theory and Non-Conventional Morphologies in the Ternary ABC Triblock Copolymers

The Leibler weak segregation theory in molten diblock copolymers is generalized with due regard for the 2nd shell harmonics contributions defined in the paper and the phase diagrams are built for the linear and miktoarm ternary ABC triblock copolymers. The symmetric linear copolymers with the middle block non-selective with respect to the side ones are shown to undergo the continuous ODT not only into the lamellar phase but also into various non-conventional cubic phases (depending on the middle block composition it could be the simple cubic, face-centered cubic or non-centrosymmetric phase revealing the symmetry of space group No.214 first predicted to appear in molten block copolymers). For asymmetric linear ABC copolymers a region of compositions is found where the weakly segregated gyroid (double gyroid) phase exists between the planar hexagonal and lamellar or one of the non-conventional cubic phases up to the very critical point. In contrast, the miktoarm ABC block copolymers with one of its arm non-selective with respect to the two others are shown to reveal a pronounced tendency towards strong segregation, which is preceded by increase of stability of the conventional BCC phase and a peculiar weakly segregated BCC phase (BCC3), where the dominant harmonics belong to the 3rd co-ordination sphere of the reciprocal lattice. The validity region of the developed theory is discussed and outlined in the composition triangles both for linear and miktoarm copolymers.Comment: 61 pages, 12 figure

Polymer-based photonic crystals

In this report, we highlight the development of polymers as 1D photonic crystals and subsequently place special emphasis on the activities in self-assembled block copolymers as a promising platform material for new photonic crystals. We review recent progress, including the use of plasticizer and homopolymer blends of diblock copolymers to increase periodicity and the role of the self-assembly in producing 2D and 3D photonic crystals. The employment of the inorganic nanoparticles to increase the dielectric contrast and the application of a biasing field during self-assembly to control the long-range domain order and orientation are examined, as well as in-situ tunable materials via a mechanochromic materials system. Finally, the inherent optical anisotropy of extruded polymer films and side-chain liquid-crystals-line polymer is shown to provide greater degrees of freedom for further novel optical designs

Structural changes of poly(butadiene)-poly(ethyleneoxide) diblock-copolymer micelles induced by a cationic surfactant: Scattering and cryogenic transmission electron microscopy studies

Nordskog A, Egger H, Findenegg GH, et al. Structural changes of poly(butadiene)-poly(ethyleneoxide) diblock-copolymer micelles induced by a cationic surfactant: Scattering and cryogenic transmission electron microscopy studies. Physical Review E. 2003;68(1): 11406.Micelles of the diblock copolymer poly(butadiene)-poly(ethyleneoxide) (B-40-b-EO62) and mixed micelles of this polymer with the cationic surfactant dodecyltrimethylammonium bromide (C(12)TAB) were investigated using static and dynamic light scattering and small-angle neutron scattering. It is shown that the surfactant induces a major structural change from large mainly rodlike aggregates to smaller spherical mixed micelles. The rodlike assemblies found in the absence of surfactant have a contour length L of ca. 500 nm and a diameter d approximate to30 nm. The spherical mixed micelles obtained upon addition of C(12)TAB possess a hydrodynamic radius of 15 nm and still contain several polymer molecules. The results of the scattering experiments are consistent with observations of the aggregates by cryogenic transmission electron microscopy