Mesomorphic ordered systems, formation

Water and isobutyric acid (IBA) have been chosen as solvents because they form a mesophase with HPC and they have a critical temperature, approximately 26 C for an IBA proportion of approximately 0.4. The phase diagram shows different regions one- or two-phase, mesomorphic, or not. The two-phase region can be segregated. The mesomorphic phase can form a gel or show cholesteric colors (25). The most important Information given by this phase diagram is that the behavior of phase separation of IBA/H2O/HPC system is governed by the extreme preference of HPC for IBA as compared with water. This results in the formation of the ordered phase in dilute HPC solutions as the IBA content in the solvent is reduced. Mesophases can be obtained for low polymer concentrations of a few percent. 

Further studies by Nishiyama et al. [34-45] showed that when taken in isolation, only one of the aromatic units within a supermolecular system has a propensity to exhibit liquid crystal phases, then the supermolecular material itself could be mesomorphic, see Fig. 5. For example, for the top molecular structure, 5 [45], in Fig. 5, only the biphenyl unit at the center of the structure supports mesophase formation, whereas the benzoate units are too isolated from the biphenyl moiety in order to affect mesomorphic behavior. The second material, 6 [45] has terminal phenyl units, which are only connected by aliphatic chains to the benzoate units. Thus in this case, the material has four aromatic units out of six which are not in positions that can enhance mesophase formation. However, the second material has similar transition temperatures and phase sequences to the first, i.e., both materials exhibit an unidentified smectic phase and a synclinic ferroelectric smectic C phase. If the third material, 7 [38], is examined, it can be seen that the mesogenic unit at the center of the supermolecule is an azobenzene unit which is more strongly supportive of mesophase behavior than the simple biphenyl moiety. Thus the clearing point is higher for this material in comparison to the other two. The attachment of the terminal phenyl unit is by a methylene spacer of odd parity, and as a consequence the smectic C phase has an anticlinic structure rather than synclinic. 

Molecular theories of mesomorphic polymers may serve to give a better insight into the mechanisms involved in the formation of ordered phases in macromolecular liquids. The importance of parameters such as chain length, chain flexibility... can be explored and the results used in synthesis of new systems with well-defined characteristics. Studies of the influence of solvents on the mesomorphic phase transition and the possibility of ordering by external fields (electric, magnetic, flow) are problems of technological in-ter>est in the spinning of fibers and in the formation of new polymer blends. 

There is considerable interest in the properties of new mesomorphic materials, which are composed of molecules with novel architectures. These include rod-coil molecules [1], polyphilic molecules [2, 3], block-copolymers [4] and dendritic molecules [5]. In many of these systems microphase separation can be used to build new materials containing structures that are ordered on the nanoscale. Examples include the formation of spheres or rods within a uniform matrix of dififerent chemical... 

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