Perforated lamella structure

Figure 15.6 Self-assembled structures of asymmetric diblock copolymers confined in a thin film, (a) and (b) Parallel cylinder structures, (c) perpendicular cylinder structures, (d) and (e) lamellar structures, and (f) perforated lamellae structure.Huinink et al. [39]. Reproduced with permission of Elsevier.

Recently, researchers paid more attention to the guided self-assembly of block copolymer thin films on a patterned surface. The patterned surface means the surface of a constrained situation is chemically or physically modified to form a pattern with specific property and size. A series of exquisite structures are found in the microphase separation of block copolymer under the patterned surface. In the theoretic work of Wu and Dzenis [43], they designed two kinds of patterned surface to direct the block copolymer self-assembly (Fig. 15.7). The self-assembled structures are found strongly influenced by the commensurability of polymer bulk period and pattern period. With mismatched patterns on two surfaces, both MC simulation [44] and SCFT researching [45] predicted the titled lamellae and perforated lamellae structures for symmetric diblock copolymers. Petrus et al. carried out a detailed investigation on the microphase separation of symmetric and asymmetric diblock copolymers confined between two planar surfaces using DPD simulation [46,47]. It is found that various nonbulk nanostructures can be fabricated by the nanopatterns on the surfaces. 

Figure 16 Structures of symmetric end-tethered Vs. (a) Spherical micelles that order into a BCC structure. An individual micelle, with tethers removed for clarity, and tether attachment points colored cyan, is shown to the right, (b) Cylindrical micelles that arrange in a hexagonally ordered bulk structure (H). An individual cylinder extracted from the system, where tethers have been removed for clarity, and attachment points are colored cyan, is shown to the right, (c) Perforated lamella structure with an individual sheet of perforated lamella that demonstrates an HC pattern shown to the right (d) Lamellar sheets where Vs locally order resulting in an SCL structure. Reprinted with permission from Nguyen, T. D. Zhang, Z. Glotzer, S. C. J. Chem. Phys. 2008,129 (24), 244903. Copyright 2008, American Institute of Physics.

Fig. 1 Phase diagram of self-assembled structures in AB diblock copolymer melt, predicted by self-consistent mean field theory [31] and confirmed experimentally [33]. The MesoDyn simulations [34, 35] demonstrate morphologies that are predicted theoretically and observed experimentally in thin films of cylinder-forming block copolymers under surface fields or thickness constraints dis disordered phase with no distinct morphology, C perpendicular-oriented and Cy parallel-oriented cylinders, L lamella, PS polystyrene, PL hexagonally perforated lamella phase. Dots with related labels within the areal of the cylinder phase indicate the bulk parameters of the model AB and ABA block copolymers discussed in this work (Table 1). Reprinted from [36], with permission. Copyright 2008 American Chemical Society...

For a strong surface field and symmetric wetting conditions, a perforated lamella (PL) phase typically develops in up to four layers of structures, with an exception for the first layer of structures at the favored film thickness. For one layer and all transition regions between terraces a Cy phase was found. 

Fig. 9. Self-organization structures of block copolymers and surfactants spherical micelles, cylindrical micelles, vesicles, fee- and bcc-packed spheres (FCC, BCC), hexagonaUy packed cylinders (HEX), various minimal surfaces (gyroid, F-surface, P-surface), simple lamellae (LAM), as well as modulated and perforated lamellae (MLAM, PLAM) (with permission from [5])...

These non-bulk structures also provide a window for the study of surface reconstruction of block copolymers [31]. It has been shown that surface reconstruction of the domains in thin films of cylinder-forming block copolymers on a chemically homogeneous surface can lead to a variety of structures, such as perforated lamellae, undulating cylinders, and spherical nodules [31, 66]. Additionally, separate research demonstrated that cylindrical domains can assume very tortuous, three-dimensional (3D) structures in films on chemically homogeneous substrates as the film thickness is increased beyond a first layer of cylinders adjacent to the substrate [29]. 

For asymmetric cylinder-forming and sphere-forming diblock copolymer thin films, experimental and theoretical studies demonstrate that a large number of morphologies such as lamellae, perforated lamellae, a layer of spheres, parallel or perpendicular cylindrical structures, and many complex hybrid morphologies spontaneously form. " These structures are sensitive to the selectivity of the confining surfaces and thickness of the film (Figure 2). 

Fig. 2.3 Typical isothermal frequency scans for PE-PEE diblocks with indicated compositions in different ordered phases (Zhao ei at. 1996). Qualitative differences between the low frequency rheological response for distinct ordered structures similar to these are observed for other diblocks. S = BCC spheres, C = hex cylinders, G = Ia3d gyroid, HPL = hexagonal perforated layer, L = lamellae. (A) G (x) G . Structural assignments of the ordered phases were made using TEM and SAXS.

Fig. 6.6 TEM images of a catenoid lamellar hexagonal perforated layer (HPL) structure in a blend of a PS-PB diblock (M = 49.9kgmor1, 51wt% PS) and PS homopolymer M = 26 kg mol 1) and a total PS volume fraction fFS = 0.67 (Disko etal. 1993). The sample was annealed at 130 °C prior to microtoming (a) view parallel to the lamellae (b) view normal to the lamellae, showing hexagonal perforations in a PI lamella.

Also in bulk block copolymers microphase-separate into ordered liquid crystalline phases. A variety of phase morphologies such as lamellae (LAM), hexagonally ordered cylinders (HEX), arrays of spherical microdomains (BCC, FCC), modulated (MLAM) and perforated layers (FLAM), ordered bicontinuous structures such as the gyroid, as well as the related inverse structures have been documented. The morphology mainly depends on the relative block length. If, for instance, both blocks are of identical length, lamellar structures are preferred. 

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