Block copolymer phases

Shi A C, Noolandi J and Desai R C 1996 Theory of anisotropic fluctuations in ordered block copolymer phases Macromolecules 29 6487... 

When studying systems with mixed fluid and solid directions, it is important to keep in mind that each solid direction should be allowed to breathe and fluid directions need to be scaled isotropically or constrained to a constant value. Allowing two fluid directions to fluctuate independently from one another allows the simulation cell to become flat like a pancake, which we certainly would like to avoid. As an example, consider Figure 15, in which a lamellar block copolymer phase is sheared. The convention would be to have the shear direction parallel to x and the shear gradient direction parallel to y. No reason exists for the simulation cell to distort such that Lxz = Lyz = 0 would not be satisfied on average, so one may fix the values of Lxz and Lyz from the beginning. As a result, one solid direction exists plus two fluid directions. We can also constrain Lxx to a constant value, because the shear direction will always be fluid and another fluid direction can fluctuate. This result means that we should allow the simulation cell to fluctuate independently in only the directions of... 

Figure 15 A lamellar block copolymer phase is reoriented through external shear. The initial phase has the direction of the lamellae parallel to the shear gradient direction. The most stable state would be to orient the director parallel to the shear and shear gradient direction. However, the reorientation process gets stuck before true equilibrium is reached. The stuck orientation is relatively stable, because the lamellae have to be broken up before they can further align with respect to the shear flow. Reprinted with permission from Ref. 56.

Figure 6.5 Illustrations of nanoscale spherical assemblies resulting from block copolymer phase separation in solution are shown, along with the chemical compositions that have been employed to generate each of the nanostructures (a) core crosslinked polymer micelles (b) shell crosslinked polymer micelles (SCKs) with glassy cores (c) SCKs with fluid cores (d) SCKs with crystalline cores (e) nanocages, produced from removal of the core of SCKs (f) SCKs with the crosslinked shell shielded from solution by an additional layer of surface-attached linear polymer chains (g) crosslinked vesicles (h) shaved hollow nanospheres produced from cleavage of the internally and externally attached linear polymer chains from the structure of (g)...

The increase of the solvent concentration in SB41 films on raising the partial pressure of chloroform vapor, and the related loss of long-range order, can be explained in terms of the so-called dilution approximation for the bulk block copolymer phases [167, 168], The above results clearly demonstrate the high sensitivity of the polymer-polymer interactions towards solvent content. Therefore, the microphase-separated structures in swollen block copolymer films can be used as a qualitative measure of the degree of swelling of the films [49, 166],... 

Block copolymer phase separation has first and foremost been studied in bulk. The mesoscale structure is determined by molecular parameters such as chain length (N), volume fractions of the components, interaction between the blocks (x) and temperature (Figure 2.6). In this Chapter, we will be concerned mainly with diblock copolymers,... 

Figure 13.6 Transmission electron micrographs of thin-sectioned PS-PI block copolymer phases (a) lamellar phase, (b) hexagonal cylindrical phase. (Reprinted with permission from Forster et al.. Macromolecules 27 6922. Copyright 1994, American Chemical Society.)...

ABC-type triblock copolymers, in which A, B, and C are all chemically distinct from each other, can form a variety of additional structures, such as a cylindrical phase ordered on a square lattice, a tricontinuous diamond phase (Mogi et al. 1992 Nakazawa and Ohta 1993), and some exquisitely delicate structures, such as cylinders decorated by rings (see Fig. 13-8) or by strands winding around them in helieal fashion (Stadler et al. 1995 Krappe et al. 1995). Recent findings have greatly expanded the known types of ordered block copolymer phases. 

High densities of defects are frequently present in ordered block-copolymer phases. 

As discussed below, the quality of the alignment (and even its direction in the case of lamellar morphology), is influenced by temperature, as well as the frequency and strain amplitude of the aligning shear field. No general theory for the alignment of block-copolymer phases has yet been developed. However, studies of a number of different block-copolymer systems show that in ordered states with cylindrical domains, shear orients the cylinders parallel to the flow, while for lamallar microdomains, two different shear-induced orientations are commonly found, depending on alignment conditions in both of these orientations, the flow direction lies in the plane of the lamellae. 

As with lamellar and hexagonal block-copolymer phases, steady or large-amplitude oscil-... 

Another example is that of lattice chain models. Simple square lattice models were established by Flory as a vehicle for calculating configurational entropies etc., and used later in the simulations of the qualitative behaviour, e.g. of block copolymer phase separation. More sophisticated models such as the bond fluctuation model, and the face centred cubic lattice chain modeP ... 

Shi and Wang (unpublished work) have recently developed a rigorous theory for extracting the elastic moduli of ordered block copolymer phases... 

Temphn, M. et al.. Organically modified aluminosilicate mesostructures from block copolymer phases. Science, 278, 1795, 1997. 

Fig. 18A, B. USAXS-patterns of A a shear-oriented nematic block copolymer phase B the oriented mesoporous monolith prepared therefrom. The shift of the Debye-Scherrer ring is due to removal of solvent during the sol-gel process [110]...

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