Polymeric liquid-crystalline phases

Secondly, thermotropic liquid crystalline polymers are characterized in a temperature range that is often too high to keep the molecular structure unchanged. The post-polymerization and decomposition are two possible results of a prolonged study of a polymeric liquid crystalline phase. There have been reports on liquid crystalline phases observable only... 

Finally, there is considerable interest in polymeric assemblies both in solution and in liquid crystalline phases [87]. In a seminal report, Meijer and co-workers [49] have synthesized dimers of module 75 (e.g. 101) and shown that its solutions have rheological properties similar to those shown by normal polymer solutions (Fig. 25). In this regard, the high dimerization constant of 75 allows a high degree of polymerization at accessible concentrations. Likewise, Lehn has shown that 1 1 mixtures of 102 103 and 33 104 form supramolecular, polymeric, liquid crystalline phases (Fig. 25). The structure of 102 103 is believed to contain a triple helical superstructure [88], whereas rigid assembly 33 104 forms a lyotropic mesophase [89]. 

In order to investigate the phase transition in the monolayer state, the temperature dependence of the Jt-A isotherm was measured at pH 2. The molecular area at 20 mN rn 1, which is the pressure for the LB transfer of the polymerized monolayer, is plotted as a function of temperature (Figure 2.6). Thermal expansion obviously changes at around 45 °C, indicating that the polymerized monolayer forms a disordered phase above this temperature. The observed temperature (45 °C) can be regarded as the phase transition point from the crystalline phase to the liquid crystalline phase of the polymerized organosilane monolayer. 

Order and Mobility are two basic principles of mother nature. The two extremes are realized in the perfect order of crystals with their lack of mobility and in the high mobility of liquids and their lack of order. Both properties are combined in liquid crystalline phases based on the selforganization of formanisotropic molecules. Their importance became more and more visible during the last years in Material science they are a basis of new materials, in Life science they are important for many structure associated functions of biological systems. The main contribution of Polymer science to thermotropic and lyotropic liquid crystals as well as to biomembrane models consists in the fact that macromolecules can stabilize organized systems and at the same time retain mobility. The synthesis, structure, properties and phototunctionalization of polymeric amphiphiles in monolayers and multilayers will be discussed. 

The source of all carbon relevant to the present context is the feedstock of hydrocarbon molecules (aliphatic, aromatic, with and without heteroatoms). Figure 10 summarizes the possibilities for their conversion into black carbon. The chemical route comprises polymerization into aromatic hydrocarbons with final thermal dehydrogenation. This process often includes a liquid crystalline phase immediately before final solidification. In this phase large aromatic molecules can sclf-organizc into parallel stacks and form well-ordered precursors for graphitic structures with large planar graphene layers. This phase is referred to... 

Liquid crystalline phases are known to couple collectively - and therefore strongly - to external electromagnetic fields, which may be used to induce local variations. If such polymeric liquid crystal phases are rapidly frozen-in, this leads to strongly anisotropic glasses. 

It is well-known that the tendency to form a liquid-crystalline phase is most pronounced for those substances which molecules have an elongated shape. Stiff-chain macromolecules are obviously good examples of this kind. Their asymmetry can be so large that they can form liquid-crystalline phase not only in the bulk but also in the solution. In the latter case, liquid crystals are called polymeric lyotropic liquid crystals. It is the theory of this type of liquid crystals that will be considered in the present paper. 

The amphiphilic polymers and copolymers offer broad aspects for applications similar to low molar mass surfactants. Modifications of solutions, e.g. with respect to their viscosity, can be performed by the variation of the degree of polymerization of the polysurfactants easily. The liquid crystalline phase... 

Fig. 11 a) Binary phase diagram of a non-ionic polysurfactant b) maximum clearing temperature of the liquid crystalline phase as function of the degree of polymerization... 

In both cases, pretransltional properties (2), the type of liquid crystalline phase and order parameters (8-9). elastic (Ifl) and rheological properties (11=12) have been the object of numerous studies or review articles. Some applications in very different fields (high modulus fibers, self-reinforced polymeric materials, electronic display devices, non-linear optics, etc.) have already been realized or are being pursued. 

This chapter focuses on the fixation of lyotropic liquid crystalline phases by the polymerization of one (or more) component(s) following equilibration of the phase. The primary emphasis will be on the polymerization of bicontinuous cubic phases, a particular class of liquid crystals which exhibit simultaneous continuity of hydrophilic — usually aqueous — and hydrophobic — typically hydrocarbon — components, a property known as bicontinuity (1), together with cubic crystallographic symmetry (2). The potential technological impact of such a process lies in the fact that after polymerization of one component to form a continuous polymeric matrix, removal of the other component creates a microporous material with a highly-branched, monodisperse, triply-periodic porespace (3). 

The microporous material exhibits in all cases a precisely controlled, reproducible and preselected morphology, because it is fabricated by the polymerization of a periodic liquid crystalline phase which is a thermodynamic equilibrium state, in contrast to other membrane fabrication processes which are nonequilibrium processes. 

Polymeric Cubic and Other Liquid Crystalline Phases. 

The first part of the book discusses formation and characterization of the microemulsions aspect of polymer association structures in water-in-oil, middle-phase, and oil-in-water systems. Polymerization in microemulsions is covered by a review chapter and a chapter on preparation of polymers. The second part of the book discusses the liquid crystalline phase of polymer association structures. Discussed are meso-phase formation of a polypeptide, cellulose, and its derivatives in various solvents, emphasizing theory, novel systems, characterization, and properties. Applications such as fibers and polymer formation are described. The third part of the book treats polymer association structures other than microemulsions and liquid crystals such as polymer-polymer and polymer-surfactant, microemulsion, or rigid sphere interactions. 

From this point of aew Flory s works give a reliable basis for a general analysis of phase equilibrium in polymeric systems involving the formation of liquid crystalline phases. In particular, this applies to the cases when these equilibria are compli-... 

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