Phase separation, block copolymers

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)...

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,... 

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 ... 

For most BC the phase diagram is characterized by the presence of an upper critical solution temperature, UCST, also known as an order-disorder transition temperature or a microphase separation temperature. Below UCST the block copolymers phase separate, while above it, an isotropic melt is obtained. Owing to the chemical... 

Comparison of the data in Tables 14 and 19 of graft and block copolymers, respectively, based on methyl methacrylate and a mesogenic methacrylate confirm that block copolymers phase separate more easily than graft copolymers. Although not exactly comparable due to the different mesogenic methacrylates, the block copolymers phase separate at shorter block lengths than the graft copolymers. In addition, the distribu-... 

Fig. 16 Tapping mode AFM height image of an etched PI-6-PFS organic-organometallic diblock copolymer film. The dots are a result of the block copolymer phase separation. Reprinted with permission from [7]. Copyright 2000, American Chemical Society...

In this group can be included the structuration driven by dewetting, evaporative self-organization, block copolymer phase separation, segregation of additives to surfaces, or template guided surface structuration. 

Properties of block copolymers phase separation in solution... 

Thus, for microphase separation xabN must be greater than 10.4. Since Xab is a measure of the chemical dissimilarity between the units (mers) in the blocks XabN represents the total dissimilarity over the whole macromolecule. Using equation 12 the minimum value of (XABN)min to bring about phase separation is about 10.4. This very simple approach provides a value for (xABN)min which is very similar to much more complex theories developed by Leibler using self-consistent field theory (Leibler, 1980). A summary of recent theoretical developments in block copolymer phase separation has been provided by Grason (Grason, 2006). 

Moller, M., and Lenz, R. W., Poly(2-vinylpyridine) block copolymers. Phase separation and electronic conductivity of iodine complexes, Makromol Chem., 190, 1153-1168... 

Figure 9 Poly(ether-urea) block copolymers phase separate after one-dimensional stacking and aggregation into nanofibres, as visualized by atomic force microscopy (AFM) phase images. (Reproduced from Ref. 34. American Chemical Society, 2006.)...

If block copolymers phase-separate, how big are the domains If the bonds holding the blocks together are maintained, then the domains must be small... 

Keywords Atomic force microscopy (AFM) Block copolymers Phase separation Self-assembly ... 

Noguchi, S. Nagano, S. Onuma, Y. Matsushita, Y Seki, X. Optical recording material using amphipathic block copolymer phase-separated monolayer, and its manufacturing method. Jpn. Kokai Xokkyo Kobo JP 2006312253, 2006 Chem. Abstr. 2006, 145, 497726. 

It was pointed out in Section 2.16.9 that anionic living polymerisation can be used to prepare ABA tri>block copolymers suitable for use as thermoplastic elastomers. In such copolymers the A blocks are normally of a homopolymer which is glassy and the B block is of a rubbery homopolymer (e.g. a polydiene such as polybutadiene or polyisoprene). The characteristic properties of these materials stems from the fact that two polymers which contain repeat units of a different chemical type tend to be incompatible on the molecular level. Thus the block copolymers phase separate into domains which are rich in one or the other type of repeat unit. In the case of the polystyrene-polydiene-polystyrene types of tri-block copolymers used for thermoplastic elastomers (with about 25% by weight polystyrene blocks), the structure is phase-separated at ambient temperature into approximately spherical polystyrene-rich domains which are dispersed in a matrix of the polydiene chains. This type of structure is shown schematically in Fig. 4.36 where it can be seen that the polystyrene blocks are anchored in the spherical domains. At ambient temperature the polystyrene is below its Tg whereas the polydiene is above its Tg. Hence the material consists of a rubbery matrix containing a rigid dispersed phase. 

In a combined experiment and simulation study, Edwards et al. studied the mechanism of chemical epitaxy in a thin lamellar PS- -PMMA on a striped surface pattern. Microphase separation was observed to initiate at the patterned surface and propagate upward through the film. This is a common mechanism observed in subsequent studies, the static chemical prepattem is a pre-nudeated origin for subsequent coarsening of the block copolymer phase separation. 

However, one must consider the interactions of each of the four materials in the system with each other. In a neat block copolymer, phase separation is dictated byxAB/ H and/. When swollen with a single solvent, the behavior depends on N, f, and/AB as well as the interaction of the solvent with each block, Xas and /bs- With the two-solvent system (we will call the solvents X and Y), we consider not only the volume fraction/, the degree of polymerization N, and the Flory-Hu ins interaction of the block copolymer /ab< but also the interaction of each solvent with each block (xax- /ay- /bx- and /by) and the interaction of the two solvents, /xy-... 

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