Liquid crystalline polymeric lyotropic

Hydrophobically modified polybetaines combine the behavior of zwitterions and amphiphilic polymers. Due to the superposition of repulsive hydrophobic and attractive ionic interactions, they favor the formation of self-organized and (micro)phase-separated systems in solution, at interfaces as well as in the bulk phase. Thus, glasses with liquid-crystalline order, lyotropic mesophases, vesicles, monolayers, and micelles are formed. Particular efforts have been dedicated to hydrophobically modified polyphosphobetaines, as they can be considered as polymeric lipids [5,101,225-228]. One can emphasize that much of the research on polymeric phospholipids was not particularly focused on the betaine behavior, but rather on the understanding of the Upid membrane, and on biomimicking. So, often much was learnt about biology and the life sciences, but little on polybetaines as such. 

Large numbers of functionalized LB films have been prepared. Highly ordered LB films have been formed by the inclusion of surface-active cobaltous phthalocyanine [168] amphiphilic TCNQ was assembled to function as conducting LB films [169] liquid-crystalline LB films, potentially capable of undergoing thermotropic or lyotropic phase transitions [170, 171], have also been generated. Spacer groups introduced into polymeric surfactants (23) helped to stabilize the LB films which they formed by decoupling the motion of pendant polymers (see Fig. 13) [172]. 

Polyoxybenzoate is a stiff chain, lyotropic liquid crystalline material, as was discussed on the basis of its copolymers with ethylene terephthalate (see Sect. 5.1.4). The crystal structure of the homopolymer polyoxybenzoate was shown by Lieser 157) to have a high temperature phase III, described as liquid crystalline. X-ray and electron diffraction data on single crystals suggested that reversible conformational disorder is introduced, i.e. a condis crystal exists. Phase III, which is stable above about 560 K, has hexagonal symmetry and shows an 11 % lower density than the low temperature phases I and II. It is also possible to find sometimes the rotational disorder at low temperature in crystals grown during polymerization (CD-glass). 

There have been a lot of studies of cholesteric films and gels in order to exploit their potential as specific optical media and as other functional materials. Most of the preparations were achieved by modification or improvement of previous attempts to immobilize the cholesteric structure of cellulose derivatives into the bulky networks either by crosslinking of cellulosic molecules with functional side-chains in the liquid-crystalline state [203], or by polymerization of monomers as lyotropic solvents for cellulose derivatives [204-206],... 

Figure 3 Liquid crystalline (A) and gel-based alignment medium (B) at various stages (A) dry PBLG and the readily prepared lyotropic mesophase. (B) Cross-linked PS as an unswollen polymer stick in a standard NMR tube (left), polymer stick directly after polymerization, fully swollen polymer stick, polymer stick swollen in an NMR tube with an effective stretching along the tube axis (right). (Reproduced from refs. 17 and 53 with permission from Wiley-VCH Verlag GmbH Co. KGaA (Copyright).)...

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. 

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. 

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). 

Statistical Theory of Polymeric Lyotropic Liquid Crystals 4 Intramolecular Liquid-Crystalline Hiase... 

First, the lyotropic phase is used as a template for the preparation of a bicontinuous silica structure, from which the polymer is removed by calcination or extraction. In the second step the porous inorganic structure is filled with monomer and crosslinker which is polymerized to form a bicontinuous organic polymer network from which the silica template is removed by treatment with hydrofluoric acid. An example for the preparation of hierarchical structures is the synthesis of bicontinuous pore structures by using two templates simultaneously [115]. In this case a liquid crystalline lyotropic phase of an amphiphilic block copolymer is used as a template together with suspended latex particles. The sol-gel process with subsequent calcination leads to a bicontinuous open pore structure with pores of 300 nm and 3 nm. 

Liquid crystals combine properties of both liquids (fluidity) and crystals (long range order in one, two, or three dimensions). Examples of liquid crystalline templates formed by amphiphiles are lyotropic mesophases, block copolymer mesophases, and polyelectrolyte-suxfactant complexes. Their morphological complexity enables the template synthesis of particles as well as of bulk materials with isotropic or anisotropic morphologies, depending on whether the polymerization is performed in a continuous or a discontinuous phase. As the templating of thermotropic liquid crystals is already described in other reviews [47] the focus here is the template synthesis of organic materials in lyotropic mesophases. 

The kinetics of polymerization of amphiphilic monomers in lyotropic mesophases has been investigated by Lester and Guymon, who found that the polymerization rate of a semifluorinated alkyl methacrylic acid in a lyotropic liquid crystal increased with the degree of order of the liquid crystalline phase [69]. 

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]. 

Liquid crystals are broadly classified as nematic, cholesteric and smectic (I)- There are at least nine distinct smectic polytypes bearing the rather mundane labels smectic A, B, C,... I, by the chronological order of their discovery. Some of the smectics are actually three-dimensional solids and not distinct liquid-crystal phases at all. There are three t s of liquid crystals. Thermotropic liquid-crystal phases are those observed in pure compounds or homogeneous mixtures as the temperature is changed they are conventionally classified into nematic, cholesteric, and smectic phases in Fig.2. Lyotropic liquid-crystal phases are observed when amphiphilic molecules, such as soaps, are dissolved in a suitable solvent, usually water. Solutions of polymers also exhibit liquid-crystalline order, the polymeric phases. Most of our knowledge about liquid crystals is based on the thermotropic phases and much of this understanding can be transferred to elucidate polymeric and lyotropic phases. 

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