Morphology of diblock copolymers

In homo-polymers, when crazes are surface-initiated, generally imder a substantial stress, premature fracture follows from craze breakdown initiated from entrapped dust particles of low adhesion to craze matter. To counteract this, various types of compliant particles having a variety of morphologies that are effective in craze initiation under lower stresses are incorporated into the homo-polymers through synthesis or blending. We discuss this practice in Chapter 13 on toughening of brittle polymers. 

Hexagonal-packed Body-centered cylinders cubic 

Clearly, the form of crazing in the diblocks is fundamentally different from that in homo-polymers discussed in Section 11.7, where the fibrillar craze matter is formed by a succession of interface convolutions at the craze tip followed by widening of the craze along its border by further plastic drawing-out of the 

In the following section we develop a craze-growth model in PS/PB diblocks with spherical domains, where in terms of the phenomenology there exists a direct parallel with the crazing in homo-polymers. The model presented here is an abbreviated form of the model described in greater detail by Schwier et al. (1985a). 

3 A model of craze growth in a PS/PB diblock copolymer with spherical PB domains 

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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... 

Fig. 1 Morphologies of diblock copolymers cubic packed spheres (S), hexagonal packed cylinders (C or Hex), double gyroid (G or Gyr), and lamellae (L or Lam). Inverse phases not shown. From [8], Copyright 2000 Wiley...

In this work, we have focused on strong surface preference with only mutual transition between the symmetrical and asymmetrical layer-type structures. SSL theory and MC simulation are further applied to investigate the self-assembled morphology of diblock copolymers confined in the nanopore. MC simulation shows that the Niayer of the concentric cylinder barrel changes with respect to the extent of frustration between the exterior radius Rex and the bulk lamellar period L0. Simultaneously, the predictions of SSL theory also show that both... 

Reiter G, Castelein G, Hoerner P, Riess G, Sommer JU, Floudas G (2000) Morphologies of diblock copolymer thin films before and after crystallization. Em Phys JE 2 319-334... 

Fig. 2. Microphase-separated morphologies of diblock copolymers. From left to right spheres, cylinders, double gyroid, lamellae. From Ref 76. Copyright (2000) Wiley-VCH Verlag GmbH.

Fig. 3. Schematic phase diagram and characteristic self-organized morphologies of diblock copolymers. Adapted from G. H. Fredrickson and F. S. Bales, Annu. Rev. Mater. Sci. 26, 501 (1996).

Yu B, Sun PC, Chen TH, Jin QH, Ding DT, Li BH, Shi A-C. Self-assembled morphologies of diblock copolymers confined in nanochannels Effects of confinement geometry J Chem Phys 2007 126 204903. 

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. 

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. 

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 phase morphology of block copolymers can also be visualized by transmission electron microscopy. Figure 10.8 shows the lamellar structure of Fluoro-PSB-IX. From diblock copolymers it is well known that the resulting microphase morphology depends on the volume fraction (< >) of the two phases. By simple adjustment of the relative block lengths we are able to synthesize block copolymers with specific structures.1718... 

Fig.23. Schematic illustration of wetting geometries expected for ultra-thin films of diblock copolymers a - parallel lamellae, b - surface (pinned) micelles, c - perpendicular lamellae. L corresponds to the equilibrium period of the lamellar morphology...

Winey KI, Thomas EL, Fetters LJ (1991) Ordered morphologies in binary blends of diblock copolymer and homopolymer and characterization of their intermaterial dividing surfaces. J Chem Phys 95(12) 9367-9375... 

In mean field theory, two parameters control the phase behavior of diblock copolymers the volume fraction of the A block /A, and the combined interaction parameter xTak- V. where Xab is the Flory-Huggins parameter that quantifies the interaction between the A and B monomers and N is the polymerization index [30], The block copolymer composition determines the microphase morphology to a great extent. For example, comparable volume fractions of block copolymer components result in lamella structure. Increasing the degree of compositional asymmetry leads to the gyroid, cylindrical, and finally, spherical phases [31]. 

In this review, we introduce another approach to study the multiscale structures of polymer materials based on a lattice model. We first show the development of a Helmholtz energy model of mixing for polymers based on close-packed lattice model by combining molecular simulation with statistical mechanics. Then, holes are introduced to account for the effect of pressure. Combined with WDA, this model of Helmholtz energy is further applied to develop a new lattice DFT to calculate the adsorption of polymers at solid-liquid interface. Finally, we develop a framework based on the strong segregation limit (SSL) theory to predict the morphologies of micro-phase separation of diblock copolymers confined in curved surfaces. 

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