Lateral microphase separation

Similar to the branches in copolymer stars and miktoarms, the grafted chains in brushes can be of different chemical compositions. Brown et al. [223] studied the microphase separation of grafted mixtures of homopolymer chains composed of immiscible A and B units and also [224] of diblock AB copolymers. In the former case, the brushes expand laterally and then experience lateral microphase separation. In the latter case, however, monomers segregate vertically to the surface forming a three layer structure. 

Several other examples have been reported in the literature in which one single BCP has been used. On the contrary, studies using blends are rather scarce. Krausch and coworkers [57] adsorbed a linear ABC triblock copolymer of poly(styrene-b-2-vinylpyridine-b-tert-butylmethacrylate) onto the SiO surface of a silicon wafer to fabricate a nanostructured support and analyze the microphase separation of a polymer blend on this substrate. The BCP used exhibits a lateral microphase separation as a consequence of the strong affinity of the middle block [ie, poly(vinylpyrrolidone) (PVP)] to the boundary surface. Interestingly, the phase separation of the homopolymers... 

Several structure sizes caused by microphase separation occurring in the induction period as well as by crystallization were determined as a function of annealing time in order to determine how crystallization proceeds [9,18]. The characteristic wavelength A = 27r/Qm was obtained from the peak positions Qm of SAXS while the average size of the dense domains, probably having a liquid crystalline nematic structure as will be explained later, was estimated as follows. The dense domain size >i for the early stage of SD was calculated from the spatial density correlation function y(r) defined by Debye and Buche[50]... 

Fig. 17. Monolayer of arborescent graft macromolecules consisting of a polystyrene core and poly(2-vlnylplrldlne) shell. Microphase separation between the blocks and strong interaction of the PVP block with mica resulted In lateral arrangement of the PS and PVP domains [89]...

Transmission Electron Microscopy. Films of all samples designated R were obtained by evaporation of toluene from solutions of the block copolymers and were observed without staining using a Hitachi Hu-125 or a JEOL JEM 100 S electron microscope. Methods of preparing the films have been described previously (24). So far, we have obtained evidence for microphase separation in only the four highest molecular-weight samples by TEM. We have not obtained continuous films of the lower molecular-weight samples we plan to examine sections of these samples later. Because of the very small compatibility of styrene and polydimethylsiloxane, however, we expect phase separation in all of these samples. 

Columnar mesomorphic behavior is observed for compound 78 because the associated lateral groups disturb the formation of smectic layers and the hydrophilic lateral chain and the hydrophobic core unit form microphase-separated structures. A variety of block molecules capable of forming mesophases have been prepared and examined in relation to phase-separated association [164]. 

Liquid crystallinity and block microphase separation both compete during the minimization of free energy of the system. As we will show later in this review, in the case of a rod-coil diblock copolymer, liquid crystallinity plays a very important role in the microphase separation process and leads to morphologies distinctly different from the conventional spheres, cylinders and lamellar microstructures and include the arrow head, zig-zag, and wavy lamellae phases [40, 41], In the case of SGLC-coil... 

PS was found, by TEM, to be microphase separated as PS cylinders in PI matrix in contrast to a lamellae stmcture expected for linear diblock copolymer of the same composition. Later, more thorough studies with a larger number of samples and covering a wider range of compositions showed that differences exist in the phase diagram for miktoarm star copolymers in comparison to the linear diblocks. The boundaries for the microstrurtures usually encountered in diblocks... 

---