OBDD phase

Bicontinuous cubic phases have not, to date, been accounted for using SSL theory. The OBDD phase has been shown to be unstable with respect to lam and hex phases (Likhtman and Semenov 1994 Olmsted and Milner 1994a,b). As discussed above, it now appears that the OBDD was a misidentified gyroid phase however, SSL calculations for the gyroid structure have not been performed as yet. A perforated layer structure was found to be unstable by Fredrickson (1991), using SSL theory following Semenov s method. 

Several ordered states distinguished by their symmetries have been identified the preferred one depends primarily on the polymer composition [29,38,39]. Some common patterns are lamellar sheets, ordered bicontinuous double diamond (OBDD), hexagonally packed cylindrical arrays, and body-centered-cubic spherical microstructures. If the volume fractions of the two halves of the polymer chain are similar, the interface between the two regions will be flat and the lamellar phase will form. However, if one block is much smaller than the other, then for packing reasons, the interface will curve toward the smaller half (see Fig. 19b), giving, in order of increasing curvature, the OBDD, cylindrical, and spherical microstructure. 

The phase diagrams of copolymer-homopolymer blends can be complex. Matsen has examined binary blends of AB copolymers with A homopolymers, that is, AB/A, and presented phase diagrams for various values of /a for the copolymer, examining the overall phase behavior, including the stability of different microphases and how they are affected by the homopolymer [44,45]. A notable conclusion of this work is that the addition of homopolymer can stabilize the OBDD and PL phases. This is attributed to the relief of packing frustration, discussed above in Section VI.C, which results from the nonuniform distribution of the homopolymer, with preferential localization at the comers of the unit cells. 

After the misidentification of double gyroid (G) morphology as OBDD became clear (Hajduk et al, 1995), theorists interest shifted towards the stability of OTDD and Matsen (1998) used a spectral implementation of SCFT to interrogate the phase behavior of symmetric (( a = = be, Xar = Zbc = and/a =/c) linear ABC triblocks in the inter-... 

Soto-Figueroa C, Rodriguez-Hidalgo MDR, Martinez-Magadan JM, Vicente L. Dissipative particle dynamics study of order-order phase transition of BCC, HPC, OBDD, and LAM structures of the poly(styrene)-poly(isoprene) diblock copolymer. Macromolecules 2008 41 3297. 

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