Diblock copolymers parallel lamellar

Theory for the self- and tracer-diffusion of a diblock copolymer in a weakly ordered lamellar phase was developed by Fredrickson and Milner (1990). They modelled the interactions between the matrix chains and a labelled tracer molecule as a static, sinusoidal, chemical potential field and considered the Brownian dynamics of the tracer for small-amplitude fields. For a macroscopically-oriented lamellar phase, they were able to account for the anisotropy of the tracer diffusion observed experimentally. The diffusion parallel and perpendicular to the lamellae was found to be sensitive to the mechanism assumed for the Brownian dynamics of the tracer. If the tracer has sufficiently low molecular weight to be unentangled with the matrix, then its motion can be described by a Rouse model, with an added term representing the periodic potential (Fredrickson and Bates 1996) (see Fig. 2.50). In this case, motion parallel to the lamellae does not change the potential on the chains, and Dy is unaffected by... 

The effect of constraints introduced by confining diblock copolymers between two solid surfaces was examined by Lambooy et al. (1994) and Russell et al. (1995). They studied a symmetric PS-PMMA diblock sandwiched between a silicon substrate, and silicon oxide evaporated onto the top (homopolymer PMMA) surface. Neutron reflectivity showed that lamellae formed parallel to the solid interfaces with PMMA at both surfaces. The period of the confined multilayers deviated from the bulk period in a cyclic manner as a function of the confined film thickness, as illustrated in Fig. 2.60. First-order transitions were observed at t d0 = (n + j)d0, where t is the film thickness and d0 is the bulk lamellar period, between expanded states with n layers and states with (n + 1) layers where d was contracted. Finally, the deviation from the bulk lamellar spacing was found to decrease with increasing film thickness (Lambooy et al. 1994 Russell et al. 1995). These experimental results are complemented by the phenomenologi-... 

The distribution of chains in a lamellar film formed by a binary blend of symmetric PS-PMMA diblocks has been probed using neutron reflectivity by Mayes et al. (1994). The microphase self-assembled parallel to the substrate, giving a lamellar stack, as for pure diblocks (see Section 2.5.1). By blending mixtures of unlabelled and selectively labelled long and sort diblocks, it was determined that short diblock copolymer chains are localized at the PS-PMMA interface, while the longer chains are selectively located at the domain centres. These results... 

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...

Weak preference to block copolymer. Figure 26 shows the MC simulated morphologies of A5B5 diblock copolymers confined in cylindrical nanopores with the different exterior radii Rex and eAS = bs = 0. It is shown that the lamellar structure forms parallel to the pore axis. However, there is a little difference between small and large Rex. The lamellar structure is not bended at small Rex as shown in Figure 26a, while it is bended like the wave-shape at large Rex as... 

When the confined surfaces suffer from a weak interaction with block copolymer, either parallel or vertical lamellar structures for AB diblock copolymer systems under flat and curved confinements could exhibit, as shown in Figure 27. From theoretical predictions (Turner, 1992 Walton et al., 1994) and simulations (Wang et al., 2000 Yin et al., 2004), the frustration between d and L0 could result in the alternative appearance of parallel lamellar and vertical lamellar structures under flat confinements. A question is naturally arisen can both concentric cylinder barrel and sector column structures appear under the curved confinement ... 

Figure 27 Schematic illustrations of lamellar morphologies for AB diblock copolymers under flat and curved confinements. The concentric cylinder barrel structure under curved confinement corresponds to the parallel lamellar structure under flat confinement (left). The sector column structure corresponds to the vertical lamellar structure (right).

In this work, a framework of the SSL theory for diblock copolymer melts confined in ring-like curved surfaces has been proposed. When the curvature approaches to zero, it reduces to the well-known SSL theory for the parallel lamellar phases. In the case of the equal confined thickness to the exterior radius, it can also be extended to the system with a nanopore confinement. Moreover, the Helmholtz energy of the concentric cylinder barrel, sector column and CMSC phases in 2D confinements based on this SSL theoretical framework can be evaluated in the convenient manner. The calculated results show that the diblock copolymer melts exhibit a layer-type transition with a similar mechanism, regardless of ring-like curved surfaces, planar surfaces, and nanopores. 

Diblock copolymers with roughly equal block lengths can microphase— separate into a lamellar phase, with alternating layers of mostly A monomer and mostly B monomer. When quenched into the lamellar phase from the isotropic phase, these layers form roughly parallel to each other locally. A polydomain texture is created from this quenching, with a typical grain size of order 0.1 pm. The oscillatory shear response of such a quenched sample is observed to have at the lowest measurable frequencies. Can this observed response be the real terminal response of the sample Is this sample a viscoelastic solid or a viscoelastic liquid ... 

PAGE 304 Problem 7.45 - rephrase the end of the second sentence. When rapidly cooled into the lamellar phase from the isotropic phase, the layers formed by diblock copolymers are roughly parallel to each other locally. ... 

In lamellar styrene-diene diblock copolymers, SANS studies showed that the segment Rg contracts to 70% of the unperturbed value parallel to the interface and expands to 160% of the unperturbed value perpendicular to the interface (Hasegawa et al 1985, 1987). These values were found for both the styrene and diene blocks. A smdy of stretching SIS block copolymers having spherical styrene phases showed that the deformation in the direction of stretch was greater than affine, while the deformation perpendicular to the stretch was much less (Richards and Welsh, 1995). 

Tsori Y, Andelman D (2001) Diblock copolymer thin 1ms Parallel and perpendicular lamellar phases in the weak segregation limit. Eiu Phys JE 5 605-614... 

In thin films of diblock copolymers, the interactions occurring at the air/film and fihn/substrate interfaces influence the miaophase separation process, and can be used to control the orientation of the morphology. For example, a preferential interaction of one of the blocks with the boundaries ( surfactant -like behavior) will favor uniformity of a lamellar phase on a macroscopic scale, with the lamellae of periodicity I parallel to the substrate [ 10,11]. The resulting film thickness will belong to a discrete spectrum of allowed values D , depending on the boundary conditions [10,12] given by... 

Fig. 5.12 Schematic of the surface-ordering process in a diblock copolymer. The top diagram shows the dibiock copolymer in a phase mixed state. This is not accessible for PS/PMMA co-polymers via solvent-casting processes. The center diagram corresponds to a microphase-separated morphology where the periodic lamellar microdomains are randomly oriented in the specimen. After annealing for 24 h at 170 °C, the copolymer exhibits a lamellae morphology oriented parallel to the surface as shown in the bottom picture. Reprinted with permission from ref. [96]...

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... 

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