Gyroid structure

A systematic comparative study of triblock terpolymers in the bulk and thin-film state was carried out on polystyrene-fo-poly(2-vinyl pyridine)-b-poly(ferf-bulyl methacrylate), PS-fr-P2VP-fr-PfBMA. A diblock precursor with a minority of PS leading to a double gyroid structure was used. Upon increase of PfBMA content this morphology changed from lamellae with... 

Addition of the middle B block to an ABC triblock terpolymer has been investigated by Suzuki et al. for the PI- -PS- -P2VP system [ 159]. Starting from the lamellar structure of the unblended triblock (0ps = 0.42) PS homopolymer was subsequently added. At fas 0.50 a morphological transformation into a gryoid structure is observed. Even if the volume fraction of PS is increased up to fas = 0.60, the cell size of the gyroid structure will remain... 

An A-B diblock copolymer is a polymer consisting of a sequence of A-type monomers chemically joined to a sequence of B-type monomers. Even a small amount of incompatibility (difference in interactions) between monomers A and monomers B can induce phase transitions. However, A-homopolymer and B-homopolymer are chemically joined in a diblock therefore a system of diblocks cannot undergo a macroscopic phase separation. Instead a number of order-disorder phase transitions take place in the system between the isotropic phase and spatially ordered phases in which A-rich and B-rich domains, of the size of a diblock copolymer, are periodically arranged in lamellar, hexagonal, body-centered cubic (bcc), and the double gyroid structures. The covalent bond joining the blocks rests at the interface between A-rich and B-rich domains. 

Fig. 4 Nanoporous membrane from an etched gyroid structure. Reproduced from [21]... 

In recent years a number of so-called complex phases, such as the bicontinuous gyroid and perforated layer structures, have been identified. The former has been established as an equilibrium structure, whereas the latter seem to be metastable structures observed during transformations to and from the gyroid structure. 

Fig. 2.23 TEM images from an/PS = 0.33, Mn = 2.7 X 104gmor1 PS-PI diblock (Hajduk el al. 1994a). (a) Approximate three-fold symmetry is evident from the [1 11] projection of the cubic structure. Inset are the Fourier transform of the image and indexed diffraction pattern. Tire inset on the right is a simulated [111] projection of the constant-thickness gyroid struct ure, (b) Another region of the same sample, showing four-fold symmetry, with a diffraction pattern, its indexation and a simulated [100] projection of the gyroid structure inset. The minority component (PS) appears light in the micrographs and simulations.

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. 

Fig. 5.19 Domain spacing (top line) obtained from SAXS for copolymer PEO75PBO54 as a function of time during the melting and crystallization programme indicated by the lower line (Mai el al. 1997). The melt has a gyroid structure.

Fig. 28 SEM images of about 60 nm thick films of SVT block terpolymers along with expected structural elements of the thin-film structure, (a) Core-shell cylinders (b) helices wound around a cylindrical core (c) (112) plane of an ideal double gyroid structure. Copyright (2002) Wiley. Used with permission from [18]...

For diblock copolymers, periodically arranged spheres (micelles), hexago-nally packed cylinders, and a lamellar phase have been observed [1]. A more complex bicontinuous cubic phase with QIasymmetry (gyroid structure) has also been identified. These supramolecular structures, with length scales on the order of 1 to 102 nm, may be controlled by changing the amount of solvent, the length of blocks, or the proportions of A and B monomeric units [128-131]. 

Cytomembrane structures consistent with the gyroid structure (and/or IPMS) were discussed first by Bouligand [15]. Quantitative comparison between the gyroid and a number of membranes can be found in [4, 55] (see also [56]),... 

Tri-block copolymer morphologies (a) Three-dimensional reconstruction of TEM images of gyroid structure in styrene isoprene styrene (Spontak, R. J. and Patel, N. P., Curr. Opin. Coll. Interface Sci, S, 334, 2000) Elsevier (b) TEM of lamellar edges in styrene butadiene styrene (Huy, T. A. et al.. Polymer, 44, 1237, 2000) Elsevier. 

M. R. J. Scherer, Double-Gyroid-Structured Functional Materials, Springer Theses, DOI 10.1007/978-3-319-00354-2 l,... 

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