Intramolecular liquid-crystalline phase

In this section, we will deal with the case of a very long chain. The particular features of the intramolecular liquid-crystalline phase for the relatively short chains will be considered in Sect. 5. 

From Eq. (4.1) one can see that coa < 1/p at p S> 1 and at any N 3 1 so that at the temperatures above the triple point temperature, the polymer volume fraction within the coil is not sufficient for the formation of the intramolecular liquid-crystalline phase. 

We see that the properties of the intramolecular liquid-crystalline phase in the long macromolecules are universal, i.e. not sensitive to the polymer chain models (compare the results of this section for the models shown in Figs. 7b-d). It is due to this universality that it has become possible to establish the main properties of the large globules using only general considerations and without referring to the special formalism. 

However, it must be recalled that the Lifshitz theory was originally formulated23 25 for the model of beads (see Fig. 7 a). In this model, each monomer is represented as a material point thus, this model cannot be used for the description of the intramolecular liquid-crystalline phase. The description of the orientational ordering, requires the generalization of the Lifshitz consideration for the models, in which the state of an elementary monomer is defined not only by its spatial position but also by its orientation (see, for example, the models of Fig. 7 b-db Such a generalization will be our first aim in this section. 

Experimental studies of liquid crystals have been used for many years to probe the dynamics of these complex molecules [12]. These experiments are usually divided into high and low-frequency spectral regions [80]. This distinction is very important in the study of liquid crystalline phases because, in principle, it can discriminate between inter- and intramolecular dynamics. For many organic materials vibrations above about 150 cm are traditionally assigned to internal vibrations and those below this value to so-called lattice modes . However, the distinction is not absolute and coupling between inter- and intramolecular modes is possible. 

Liquid crystals, as the name implies, are condensed phases in which molecules are neither isotropically oriented with respect to one another nor packed with as high a degree of order as crystals they can be made to flow like liquids but retain some of the intermolecular and intramolecular order of crystals (i.e., they are mesomorphic). Two basic types of liquid crystals are known lyotropic, which are usually formed by surfactants in the presence of a second component, frequently water, and thermotropic, which are formed by organic molecules. The thermotropic liquid-crystalline phases are emphasized here they exist within well-defined ranges of temperature, pressure, and composition. Outside these bounds, the phase may be isotropic (at higher temperatures), crystalline (at lower temperatures), or another type of liquid crystal. Liquid-crystalline phases may be thermodynamically stable (enantiotropic) or unstable (monotropic). Because of their thermodynamic instability, the period during which monotropic phases retain their mesomorphic properties cannot be predicted accurately. For this reason it is advantageous to perform photochemical reactions in enantiotropic liquid crystals. 

This article deals with some topics of the statistical physics of liquid-crystalline phase in the solutions of stiff chain macromolecules. These topics include the problem of the phase diagram for the liquid-crystalline transition in die solutions of completely stiff macromolecules (rigid rods) conditions of formation of the liquid-crystalline phase in the solutions ofsemiflexible macromolecules possibility of the intramolecular liquid-crystalline ordering in semiflexible macromolecules structure of intramolecular liquid crystals and dependence of die properties of the liquid-crystalline phase on the microstructure of the polymer chain. 

In contrast to polypeptides that have many possible conformations, poly(hexyl isocynate) is known to have a stiff rodlike helical conformation in the solid state and in a wide range of solvents, which is responsible for the formation of a nematic liquid crystalline phase.45-47 The inherent chain stiffness of this polymer is primarily determined by chemical structure rather than by intramolecular hydrogen bonding. This results in a greater stability in the stiff rodlike characteristics in the solution as compared to polypeptides. The lyotropic liquid crystalline behavior in a number of different solvents was extensively studied by Aharoni et al.48-50 In contrast to homopolymers, interesting new supramolecular structures can be expected if a flexible block is connected to the rigid polyisocyanate block (rod—coil copolymers) because the molecule imparts both microphase separation characteristics of the blocks and a tendency of rod segments to form anisotropic order. 

FLUORESCENCE QUENCHING OF PYRENE AS A MONITOR OF INTERMOLECULAR DIFFUSION AND INTRAMOLECULAR CHAIN BENDING IN CHOLESTERIC LIQUID CRYSTALLINE PHASES(1)... 

The rates of Intramolecular processes in anisotropic media (such as cholesteric liquid-crystalline phases) are a function of the same solvent and solute properties mentioned above and, additionally, the exigencies imposed by solvent order on the frequency and orientations of head-to-tall coll is ions(36). The importance of the latter considerations is demonstrated by the... 

Fluorescence Quenching of Pyrene as a Monitor of Inter-molecular Diffusion and Intramolecular Chain Bending in Cholesteric Liquid Crystalline Phases(l)... 

The fact that mutually different cross sectional patterns were observed in the SC-2D NMR spectrum where 7 was chosen to be 0 ms indicates that both inter- and intramolecular cross relaxation rates and spin flip-flop rates between interacting pairs of protons are relatively slow. This can be understood if one considers that dipolar interactions are partially averaged out by fast translational and rotational molecular motions in the liquid crystalline phase in contrast to the solid phase. 

Although measurements performed on unoriented samples gave evidence of new intramolecular motions in melt phases of scLCPs, for studies of molecular dynamics in liquid crystalline phases DR... 

Sixou et al. (101) showed the circular dichroism of cholesteric CTA solutions in TFA depends on the CTA molecular weight. The intensity of the circular dichroic peak increases with molecular weight. Meeten and Navard (97) studied gel formation and liquid crystallinity in TFA-H2O solutions of CTA. When water was added to a liquid crystalline solution of CTA in TFA a gel phase formed presumably by the formation of crosslinks due to hydrogen bonding. They interpreted their results that liquid crystalline ordering involves both inter- and intramolecular forces. 

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