Copolymer segregation

Many block copolymers segregate into two phases in the solid state if the sequence lengths of the blocks are long enough. Segregation is also influenced by the chemical dissimilarity of the components and the crystallizability of either or both components. This two-phase morphology is generally on a microscale with domain diameters of the order of I0 -10 cm. 

The basic assumption of the de Gennes-Leibler approach is that the copolymers segregated at the interface are in equilibrium with the free diblocks incorporated (at concentration < 0 in the host matrix homopolymer P in the bulk of the sample (see Fig. 33). It means that the chemical potentials pbrush and pbu k of the copolymers at the interface and in the bulk are equal, i.e. ... 

Fig. 37. Variation of the brush height L with the surface coverage o, as evaluated by NRA (Fig. 36) [241] for Pl-dPS (N=893) copolymers segregated at a free surface of a PS matrix with P=88 (O), 495 (X), 3173 ( ) and as determined by SIMS [249] for (COOH)dPS (N= 929) grafted onto the silicon substrate of PS(P=6442) matrix (V). Solid lines mark the variation L°cq1/3 concluded for the data (O) and L°cq1/2 for the data ( ) and (V). A horizontal arrow shows the brush radius of gyration, while a vertical arrow marks the equi-o situation described in details by Fig. 39 (here 2=a3)...

Another range of matrix molecule sizes P=88-3173 was used in our study [251] on PI (polyisoprene, NA=114)-dPS (N=893) diblock copolymer segregating to interfaces created by polystyrene P-mer with vacuum and silicon substrate. The used PS molecular weights covers the wet and dry brush regime. In Fig. 40a we present typical composition-depth profiles of Pl-dPS obtained at the vacuum ( external ) interface of PS host matrix with P varied (P=88,495, and 3173), but constant bulk diblock concentration < )00=3.2(5)%. The surface peak and a related surface excess z (and coverage a) increases with P. This is even... 

Critical micelle concentration ( >cmc is expected to decrease strongly with diminished diblock asymmetry rc as low rc values favor easier creation of highly curved micelle interfaces. Theory of micelle formation [231,260] also indicates that the overall copolymer degree of polymerization Nc, as well as the anchor -homopolymer interaction parameter %AP have to be considered to explain properly the onset of micelle segregation as observed by Shull et al. [260]. Using this theory, experimenters are able to choose systems where only individual copolymers segregate. 

The basic assumption of this approach is that the long and short copolymers segregated at the interface are in equilibrium with the long and short diblocks, respectively, incorporated (at concentration ( >s and ( >L) in the bulk of PS matrix film. This is expressed (see Eq. 64) by equating the chemical potentials of the copolymers at the interface (M-Sbrush an PLbrush) with those in the bulk (psbll k and... 

PS P(S-b-VP) Studied M, effects of di-block copolymer segregation at the interface using the segregation isotherms. A normalized interfacial thickness was found a universal function of that portion of the block copolymer chemical potential due to chain stretching. Dai and Kramer, 1994... 

The tendency considered in section 12.2 for polymers of different types to segregate applies for the true copolymers, i.e. excluding IPNs, just as it does to blends. If one component is a very minor component or if the polymer is a random copolymer, segregation does not generally take place, but in block copolymers in which the minor components form more than a certain proportion of the whole, segregation generally takes place in some range of temperatures. The important difference here is that... 

Surface segregation Surface/interfacial energy Layered segregation Nanometer Block copolymer segregation from blends afford nano-structured interfaces [4, 142, 143]... 

A crucial aspect on polymer blends containing block copolymers concerns the concentration of block copolymer both in bulk and at the surface. The former can be controlled in the design of the initial blend and the latter depends not only on the amount initially introduced in the blend but also on the eventual surface segregation. In Fig. 5.18 is schematically illustrated the block copolymer arrangement of binary blends with variable amount of block copolymer. At low concentrations (a, b) the block copolymer can reside either in the bulk or at the interface and the amount of block copolymer segregated at the interface is directly related to the... 

There have been only few reports on nanotube formation from the self-assembly in block-selective solvents of copolymers consisting of only coiled blocks. Since nature abhors vacuum, the spontaneous formation of tubular structures from block copolymers in bulk has not been reported and is probably impossible. While the direct preparation of block copolymer nanotubes by self-assembly has been so far difficult, it has been relatively easy to prepare cylindrical nanoaggregates or micelles from ABC triblock copolymers in selective solvents for A only. In such aggregates or micelles, the A block comprises the corona and the C and B blocks comprise the core/shell cylinders. In bulk at the right triblock copolymer composition, the different blocks of an ABC triblock copolymer segregate predictably into C and B core/shell cylinders dispersed in the A matrix [50,51], if the interfacial tension between the A and C blocks are comparable to that between the A and B blocks and that... 

A.N. Semenov, Theory of diblock-copolymer segregation to the interface and free surface of a homopolymer layer, Macromolecules 25 (1992) 4967-4977. 

Block Copolymer Segregation and Surface Morphology. The morphology of S3rmmetric diblock copolymer thin Aims has been studied extensively with traditional techniques (35-48). These studies foimd surface induced formation of lamellae with thickness equal to the equiUbriiun lamellar thickness Lo parallel to the substrate. The lamellae form smooth Aims when the total film thickness h is equal to an integral multiple m of Lq, h mLo for one block segregating to both the substrate and air interfaces and h (m + )Lo for one block preferring... 

For a block copolymer system where the differences in surface energy between the two components is less, wetting constraints can lead to surface heterogeneity (62). For the same composition, block copolymers, segregate more effectively to the surface than graft copoljuners, which in turn are more surface active than random copolymers, though problems with microphase separation are reduced for random copolymers (61). Other chain architectures have been investigated and also been shown to he surface active (67). 

Segmentcopolymer, segmentieites Copolymer segregate segregieren, aufspalten ... 

Dai KH, Kramer EJ (1994) Molecular weight dependence of diblock copolymer segregation at a polymer/polymer interface. J Polym Sci B Polym Phys 32 1943-1950... 

Dai KH, Norton LI, Kramer EJ (1994) Equilibrium segment density distribution of a diblock copolymer segregated to the polymer lymer interface. Macromolecules 27 1949-1956... 

Block copolymers represent the best-understood and simplest amphotropic materials studied to date. In such macromolecules, two chemically different blocks (e.g., polyst5n ene, PS, and polyisoprene, PI) are joined together by covalent bonds, so that these incompatible blocks cannot separate into distinct macroscopic phases. X-ray diffraction and electron-microscopy have established that the units of block copolymers segregate into microdomains (micro-phase or rather nano-phase separation), and produce well-developed liquid crystalline phases. ... 

---