Diblock copolymers morphologies

Figure 19.2. Schematic illustration of the conventional AB diblock copolymer morphologies superimposed on a typical phase diagram calculated by mean field theory for this type of copolymer. The volume fraction of block A is denoted by fA, the dimensionless effective... 

Fig. 12.12 Some examples of diblock copolymer morphologies. Transmission electron micrographs of stained samples of (a) the lamellar phase of a polystyrene-polyisoprene (PS-PI) diblock with PS fraction 0.64 (b) the hexagonal phase of a PS-poly(2-vinylpyridene) diblock with fps = 0.35 and (c) and (d) the gyroid phase of a PS-PI diblock with fps = 0.39, showing projections with approximate threefoid and fourfoid symmetries, respectiveiy. Aii sampies were rapidiy cooied from the meit and thus exhibit the meit-state morphoiogy. (Reprinted with permission from the American Chemicai Society.)...

With increasing amoimt of triblock copolymer, blends of lamellar SBT triblock copolymers with the asymmetric SB diblock copolymer form core-shell spheres, core-shell cylinders, core-shell double gyroids, and lamellae (Fig. 34). T forms the core domains in these morphologies, which can be considered as coreshell analogues of the well-known diblock copolymer morphologies (76). 

Rgure 1 Schemes for different diblock copolymer morphologies. From left to right the volume fraction of one component increases. The morphologies are body-centered cubic spheres (BCC), hexagonally packed cylinders (H), gyroid (G), lamellae (L). 

This simulation technique can also be applied to calculate the free energy of grain boundaries and T-junctions (see Figure 5.9) or the free energy difference of diblock copolymer morphologies on chemically patterned surfaces (cf Figure 5.10) [146]. 

This particular technique was introduced to the polymer literature by Matsen and Schick [83] in the context of diblock copolymer morphologies. The technique is based on the series expansion of any unknown function in terms of suitable basis functions and the numerical work is carried out to compute the coefficients of different terms in the series. For example, to solve Eq. (6.103), let us approximate space-dependent quantities such as h(r, t) and w(r) by a finite series in terms of orthonormal basis functions, that is, h(r, t) %(0g( ) d... 

Annis B K, Noid D W, Sumpter B G, Reffner J R and Wunderlich B 1992 Application of atomic force microscopy (AFM) to a block copolymer and an extended chain polyethylene Makromol. Chem., Rapid. Commun. 13 169 Annis B K, Schwark D W, Reffner J R, Thomas E L and Wunderlich B 1992 Determination of surface morphology of diblock copolymers of styrene and butadiene by atomic force microscopy Makromol. Chem. 193 2589... 

It is well known that block copolymers and graft copolymers composed of incompatible sequences form the self-assemblies (the microphase separations). These morphologies of the microphase separation are governed by Molau s law [1] in the solid state. Nowadays, not only the three basic morphologies but also novel morphologies, such as ordered bicontinuous double diamond structure, are reported [2-6]. The applications of the microphase separation are also investigated [7-12]. As one of the applications of the microphase separation of AB diblock copolymers, it is possible to synthesize coreshell type polymer microspheres upon crosslinking the spherical microdomains [13-16]. 

The chain arrangement of this morphology was schematically proposed as in Fig. 10. The cell of the microsphere has a hexagonal surface, and the AB diblock copolymers form a bilayer between the microspheres. From this schematic arrangement, the optimal blend ratio of the AB block copolymer in this system was calculated as 0.46. This value was very close to the blend ratio of the AB type block copolymer 0.5 at which the blend showed the hexagonal packed honeycomb-like structure. 

Laser ablation of polymer films has been extensively investigated, both for application to their surface modification and thin-film deposition and for elucidation of the mechanism [15]. Dopant-induced laser ablation of polymer films has also been investigated [16]. In this technique ablation is induced by excitation not of the target polymer film itself but of a small amount of the photosensitizer doped in the polymer film. When dye molecules are doped site-selectively into the nanoscale microdomain structures of diblock copolymer films, dopant-induced laser ablation is expected to create a change in the morphology of nanoscale structures on the polymer surface. 

As aforementioned, diblock copolymer films have a wide variety of nanosized microphase separation structures such as spheres, cylinders, and lamellae. As described in the above subsection, photofunctional chromophores were able to be doped site-selectively into the nanoscale microdomain structures of the diblock copolymer films, resulting in nanoscale surface morphological change of the doped films. The further modification of the nanostructures is useful for obtaining new functional materials. Hence, in order to create further surface morphological change of the nanoscale microdomain structures, dopant-induced laser ablation is applied to the site-selectively doped diblock polymer films. 

For symmetric PS-fo-P4VP (20 000 19 000) diblock copolymer films with the wormlike phase separation structures, the TCPP-doped films were irradiated using one laser shot with a fluence of 150 mJ cm in air. The ablation phenomenon is observed for this irradiation fluence (Figure 12.5c and f), but it is difficult to conclude that this is a selective ablation of the doped-P4VP parts. We cannot deny the possibility that the decomposition of the P4VP parts affects the PS parts because of the existence of large interfaces between the two symmetric blocks in wormlike structures. Thus, for the site-selective ablation of diblock copolymer films, the surface morphology of the phase separation structures is one of the most important parameters. 

Machida, S., Nakata, H., Yamada, K. and Itaya, A. (2007) Morphological change of a diblock copolymer film induced by selective doping of a photoactive chromophore./, Polym. Sci. B, Polym. Phys. Ed., 45, 368-375. 

Zhao, J., Jiang, S., Ji, X., Lijia, L.An. and Jiang, B. (2005) Study of the time evolution of the surface morphology of thin asymmetric diblock copolymer films under solvent vapor. Polymer, 46, 6513-6521. 

Diblock copolymers PEO-fo-PS have been prepared using PEO macroinitiator and ATRP techniques [125]. The macroinitiator was synthesized by the reaction of monohydroxy-functionalized PEO with 2-chloro-2-phenylacetyl-chloride. MALDI-TOF revealed the successful synthesis of the macroinitiators. The ATRP of styrene was conducted in bulk at 130 °C with CuCl as the catalyst and 2,2 bipyridine, bipy, as the ligand. Yields higher than 80% and rather narrow molecular weight distributions (Mw/Mn < 1.3) were obtained. The surface morphology of these samples was investigated by atomic force microscopy, AFM. 

The best-known and simplest class of block copolymers are linear diblock copolymers (AB). Being composed of two immiscible blocks, A and B, they can adopt the following equilibrium microphase morphologies, basically as a function of composition spheres (S), cylinders (C or Hex), double gyroid (G or Gyr), lamellae (L or Lam), cf. Fig. 1 and the inverse structures. With the exception of the double gyroid, all morphologies are ideally characterized by a constant mean curvature of the interface between the different microdomains. 

Even more complex structures have been described. For example, chirality of blocks may lead to other morphologies. A polystyrene-fc-poly-(L-lactide) diblock copolymer, PS-fr-PLLA, constituting both achiral and chiral blocks was reported to form an array of hexagonally packed PLLA nanohelices with a left-handed helical sense in the bulk state (Fig. 3). The structure was found... 

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. 

The effects of composition distribution on the morphology of PS-fc-P2VP diblock copolymers were investigated by Matsushita et al. [160]. They produced PS- -P2VP samples with various composition distributions but with constant average composition by blending. If the polydispersity indices of each block were lower than 1.7, the expected lamellar domains were detected (Fig. 49). 

The effect of blending an AB diblock copolymer with an A-type homopolymer has been the subject of many research activities. On a theoretical basis the subject was investigated e.g. by Whitmore and Noolandi [172] and Mat-sen [173]. If a diblock exhibiting lamellae morphology is blended with a homopolymer of high molecular weight, macrophase separation between the... 

Fig. 62 Morphology variation of blends of two diblock copolymers as/s,- (i = 1, 2, 3) in parameter space of chain length ratio r and ip-ps- Upper line Morphologies of asymmetric (as) and three symmetric (si, S2 and S3) PS-fc-PI copolymers. From [186]. Copyright 2001 American Chemical Society...

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