Cylindrical block copolymer self-assembl

Block copolymer self-assembly is a very promising alternative to make cylindrical polymer brushes. These brushes can replace the function and roles of molecular bmshes in many fields however, if the response of the main chain is necessary or in the case of multiblock copolymer side chains, they will fail to satisfy the application. 

Sdf-assembled materials, such as block copolymers, hold promise for patterning on length scales that are difficult to achieve by photolithography. As described in further detail below, block copolymers can self-assemble into a variety of morphologies including those that are spherical, cylindrical, and lamellar. In order for block copolymer self-assembly to be realistically applicable for templat-ing applications in thin films, defert-liee self-assembly must be obtained over large domains, in addition to control of the orientation of morphology formed in the thin films. 

Beyond a characteristic temperature Todt [14,20], diblock copolymers self-assemble into microphase-separated morphologies. The theoretically predicted equilibriiun states of such ordered phases correspond to perfect superlattices with various symmetries depending on the volume ratio of both blocks. In particular, lamellar (synunetric diblocks), cylindrical (asymmetric diblocks), and spherical (strongly asynunetric diblocks) morphologies are expected and have been observed [2], For typical copolymers, the characteristic length scale of these microphases is in the range from about lOnm up to some 100 nm. It is justified to say that in the bulk, microphase-separated block-copolymers represent ordered nano-structures. 

The simplest of BC architectures is that of the linear AB diblock, consisting of a chain of A monomers covalently bonded to a chain of B monomers. Linear diblock copolymers self-assemble into various morphologies such as spherical, cylindrical, gyroid and lamellae depending on the volume fraction /a of one block relative to the other, each resulting in unique patterning capabilities. Figure 25.2 (Bates and Fredrickson, 1999). 

Time-resolved in situ Small Angle Neutron Scattering (SANS) investigations have provided direct experimental evidence for the initial steps in the formation of the SBA-15 mesoporous material, prepared using the non-ionic tri-block copolymer Pluronic 123 and TEOS as silica precursor. Upon time, three steps take place during the cooperative self-assembly of the Pluronic micelles and the silica species. First, the hydrolysis of TEOS is completed, without modifications of the Pluronic spherical micelles. Then, when silica species begin to interact with the micelles, a transformation from spherical to cylindrical micelles takes place before the precipitation of the ordered SBA-15 material. Lastly, the precipitation occurs and hybrid cylindrical micelles assemble into the two-dimensional hexagonal structure of SBA-15. 

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... 

Gohy JE, Lohmeijer BGG, Alexeev A, Wang XS, Manners 1, Winnik MA, Schubert US (2004) Cylindrical micelles from the aqueous self-assembly of an amphiphilic poly(ethylene oxide)-b-poly(ferrocenylsilane) (PEO-b-PES) block copolymer with a metallo-supramolecular linker at the block junction. Chem Eur J 20 4315 323... 

Figure 9.12 (a) AFM image of spin-cast 15d 16d from benzene showing cylindrical nanodomains from the microphase separation of the supramolecular block copolymer and (b) AFM image of spin-cast 15b 16b from benzene showing self-assembled fibers. 

Manners, Winnick, and their collaborators22 have studied the self-assembly into cylindrical micelles of block copolymers formed from poly(ferrocenylsilanes) (R/R = Me/Me) and poly(dimethylsiloxane). By ensuring that the poly(dimethylsiloxane)... 

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