Bulk microphase separation

In addition to the previously mentioned driving forces that determine the bulk state phase behavior of block copolymers, two additional factors play a role in block copolymer thin films the surface/interface energies as well as the interplay between the film thickness t and the natural period, Lo, of the bulk microphase-separated structures [14,41,42], Due to these two additional factors, a very sophisticated picture has emerged from the various theoretical and experimental efforts that have been made in order to describe... 

Dwight D, McGrath JE, Lawson G, Patel N,York G (1989) Surface and bulk microphase separation in siloxane-containing block copolymers and their blends The roles of composition and kinetics from multiphase macromolecular systems. BM Culbertson (ed) Plenum, pp 265-288... 

Beyond a characteristic temperature Todt [14,20], diblock copolymers self-assemble into microphase-separated morphologies. The theoretically predicted equilibriiun states of such ordered phases correspond to perfect superlattices with various symmetries depending on the volume ratio of both blocks. In particular, lamellar (synunetric diblocks), cylindrical (asymmetric diblocks), and spherical (strongly asynunetric diblocks) morphologies are expected and have been observed [2], For typical copolymers, the characteristic length scale of these microphases is in the range from about lOnm up to some 100 nm. It is justified to say that in the bulk, microphase-separated block-copolymers represent ordered nano-structures. 

Polymer-polypeptide hybrid block copolymers are able to self-assemble either in bulk (microphase separation) or in selective solvents (micellization), like conventional block copolymers, and in addition are organized within the microphases into a-helix or j5-sheet... 

Blockcopolymer microphase separation [9] Depending on the length of chemically different blocks of monomers in a block copolymer, ordered nanostructures can be obtained in bulk samples and thin films. The film morphology can differ significantly from the bulk morphology, but because the structure is determined by the pair-pair interaction of monomers and/or an interface, and it is a thermodynamically stable structure, it is classified as self-assembly. 

The viscoelastic effects on the morphology and dynamics of microphase separation of diblock copolymers was simulated by Huo et al. [ 126] based on Tanaka s viscoelastic model [127] in the presence and absence of additional thermal noise. Their results indicate that for

bulk modulus of both blocks, the area fraction of the A-rich phase remains constant during the microphase separation process. For each block randomly oriented lamellae are preferred. 

Fig. 45 Simulated pattern evolution during microphase separation for a = 0.4 with A having a 10 times higher (a) and lower (b) bulk modulus than B. Black-. A-rich regions white-. B-rich regions. From [126]. Copyright 2003 American Chemical Society...

Predicting the characteristic sizes and morphologies of these nanostructures has been an intense topic of investigation from both the theoretical and experimental points of view. Critical parameters are the degree of polymerization and the volume fraction of the constituent blocks, as well as the Flory-Huggins parameter between them. More complete information about microphase separated structures in bulk block copolymers can be found in the book of Hamley [2],... 

F-BDAF Tg for various blend compositions, see Fig. 14. The microphase-separated morphology further manifests itself in the self-adhesion behavior of polyimide films derived from such mixtures. For mixture containing at least 25 wt% of the flexible component, peel tests of polyimide bilayer samples prepared by solution casting, bulk failure of the test specimens was observed. Since the flexible component contained fluorine, the samples could be examined by X-ray photoelectron spectroscopy to determine the surface composition. At only 10% loading, the flexible component comprised 100% of the top 75 A of the sample. The surface segregation of the flexible component is believed to be responsible for the adhesion improvements. 

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],... 

Figure 18c displays swelling kinetics of two SV films with the same initial thickness but different microphase-separated structures. The curves show up to 10% larger swelling (smaller poi) of SV films with the initial bulk lamella morphology as compared to the films with the non-bulk micelle phase [119],... 

Heteropolymers can self-assemble into highly ordered patterns of microstructures, both in solution and in bulk. This subject has been reviewed extensively [1,123-127]. The driving force for structure formation in such systems is competing interactions, i.e., the attraction between one of the monomer species and the repulsion between the others, on the one hand, and covalent bonding of units within the same macromolecule, on the other hand. The latter factor prevents the separation of the system into homogeneous macroscopic phases, which can, under specific conditions, stabilize some types of microdomain structures. Usually, such a phenomenon is treated as microphase separation transition, MIST, or order-disorder transition, ODT. 

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