Block copolymers, self-assembling microdomains

Self-Assembled Microdomain Patterns from Block Copolymers. 186... 

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 ability of block copolymers to self-assemble into organized microdomain (MD) structures when the thermodynamic repulsion between the constituents is high enough seems to be fairly well understood. This is particularly true in the case of amorphous diblock copolymers where phase diagrams for particular systems have been successfully predicted and experimentally proven [1-5]. 

Abstract This article is a review of the chemical and physical nature of patternable block copolymers and their use as templates for functional nanostructures. The patternability of block copolymers, that is, the ability to make complex, arbitrarily shaped submicron structures in block copolymer films, results from both their ability to self-assemble into microdomains, the bottom-up approach, and the manipulation of these patterns by a variety of physical and chemical means including top-down lithographic techniques. Procedures for achieving long-range control of microdomain pattern orientation as well... 

The self-assembly of block polymers, in the bulk, thin film and solution states, produces uniformly sized nanostructured patterns that are very useful for nanofabrication. Optimal utilization of these nanoscopic patterns requires complete spatial and orientational control of the microdomains. However, the microdomains in the bulk state normally have grain sizes in the submicron range and have random orientations. In block copolymer thin films, the natural domain orientations are generally not desirable for nanofabrication. In particular, for composition-asymmetric cylindrical thin films, experimental... 

The formation of bottom-up block copolymer patterns within or on top-down substrate patterns is the basis for so-called templated self-assembly processes, in which long-range order and orientation of microdomain patterns can be imposed by a template or guide . These top-down templates can take a variety of forms including periodic thickness profiles and chemically patterned surfaces. 

With recent discoveries in the self-assembly of block copolymers, a large step is now being taken towards industrial applications. However, the spontaneous process of microphase separation leads to the formation of polycrystalline microdomain arrays consisting of randomly oriented regions, which limits the potential... 

The viscoelastic properties of concentrated solutions of styrene-butadiene star-block copolymers were studied by Masuda et al. [296] in good solvents for both blocks and in selective ones. A significant dependence of the loss and storage moduli on the strain amplitude was observed in the case of dibutylphthalate, a selectively good solvent for the PS blocks at temperatures below 60 °C, which indicates the presence of a microdomain structure due to self assembling of the insoluble blocks. At a certain value of the applied strain the microdomain structure in solution was disrupted. 

Investigations on the self-assembly in thin films of an amorphous P2VP-PS-P2VP triblock copolymer, forming cylindrical microdomains in bulk, showed that the orientation of microdomains due to the P2VP/substrate interactions persisted in the entire film in contrast to the diblock case [14], This was viewed as a result of the formation of an interconnected structure in the triblock coming from the formation of loops within the microdomains. More recently, AFM and SAKS measurements on a PEO-PBO-PEO amorphous-semicrystalline triblock thin film revealed the presence of a semicrystaUine PEO monolayer at the substrate, comprised of unfolded chains, and PBO blocks at the air/polymer siuface in a looped conformation (15]. 

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