Block copolymers microphases

The Alexander approach can also be applied to discover useful information in melts, such as the block copolymer microphases of Fig. 1D. In this situation the density of chains tethered to the interface is not arbitrary but is dictated by the equilibrium condition of the self-assembly process. In a melt, the chains must fill space at constant density within a single microphase and, in the case of block copolymers, minimize contacts between unlike monomers. A sharp interface results in this limit. The interaction energy per chain can then be related to the energy of this interface and written rather simply as Fin, = ykT(N/Lg), where ykT is the interfacial energy per unit area, q is the number density of chain segments and the term in parentheses is the reciprocal of the number of chains per unit area [49, 50]. The total energy per chain is then ... 

Keywords Self-Assembly Blend Block copolymer Microphase separation ... 

Fig. 9 a Chemical structure of the diblock copolymer and the six-point H-bonding. b Deposition of NPs onto block copolymer microphase separated film, c AFM image indicating the specific deposition of NPs. Reprinted with permission from [56]... 

After hydrolysis of the films, different topographical and phase images are observed, as shown in Fig. 3.58 c and d. Block copolymer microphase separation is more pronounced and the phase images in particular reveal the presence of small features on top of the elevated worm-like features. These observations may be attributed to the fact that the PtBA groups have reacted to polyacrylic acid, which now swells due to uptake of water from the ambient air. The measured roughness increases to 5 nm. 

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. 

Croot R D, T J Madden and D J Tildesley 1999 On the Role of Hydrodynamic Interachons in Block Copolymer Microphase Separation. Journal of Chemical Physics 110 9739-9749. 

Ferroelectric liquid crystals (FLC) are of great interest due to their fast electro-optical response which is about 1,000 times faster than conventional twisted nematic cells [131]. The geometry used is called a surface stabilized FLC cell which utilizes a very thin gap (=2 pm) to unwind the FLC supramolecular pitch (=1-2 pm) since the bulk FLC materials do not show macroscopic polarization. This very thin gap, however, leads to difficulties in manufacturing large panels and very poor shock resistance. Researchers have proposed the concept of microphase stabilized FLC [79,109, 130] using FLC-coil diblock copolymers for electro-optical applications as shown in Fig. 15. This concept takes advantage of ferroelectric liquid crystallinity and block copolymer microphase separation since the block... 

Yielding in Biock Copoiymers. While polymer blends show macrophase-separated morphologies, which often lead to a deterioration of mechanical properties because of the immiscibility of the components, in block copolymers microphase-separated structures at the typical size scale 10-100 nm... 

Figure 2. Block copolymer microphase separation with lanthanide complex at the block junction (lamellar morphology shown).

Key words Block copolymer -microphase separation - doublediamond - computer simulation... 

The stability of block copolymer microphases results from a balance between the enthalpy penalty for curvature of the interface between microdomains, the entropy associated with localizing junctions between the blocks at the interface and the entropy associated with maintaining a uniform density, which leads to the stretching of chains to fill space. Again, considering AB diblock copolymers as the simplest case, in a... 

Frisbie and Hillmyer used the hydroxyethyl-terminated polythiophene in Scheme 50 as a macroinitiator for the ring-opening polymerization of D,L-lactide (Scheme 52) [150]. The hydroxy-terminated polythiophene was converted to the corresponding aluminum alkoxide macroinitiator with triethylaluminum, followed by ring-opening polymerization of the lactide to yield a block copolymer of polythiophene and polylactide. In thin films of the block copolymers, microphase-separated domains were formed. Upon chemical etching of the polylactide block, nanopitted film, where the crystallinity of the polythiophene phase remained, was observed. 

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