Liquid crystals sequence

For the liquid crystal polyesters the basic structural units are derived from such materials as 5-hydroxybenzoic acid, terephthalic acid and hydroquinone. Some basic sequences from such materials are shown in Figure 25.25. 

Figure 25.25. Typical sequences found in intractable liquid crystal polymers with >400°C...

Linear chain polymers with repeating sequences of hard and soft segments Possibility of formation of liquid crystal polymers and thermoplastic elastomers... 

Based on a known synthesis of spiro compounds with six-membered rings [63] we succeeded in the stepwise assembly of terminal substituted mono-[64] and dispiranes [65]. Hereby the cyclisation of the dibromide 35 with TOSMIC (Iter. 1) is the keystep of the reaction sequence as the initial ketone functional group (36) is recovered. Four subsequent reactions led to the spirodibromide 40 (Iter. 2). Final spirocyclisation afforded the dispirane 41, representing a precursor for new calamitic liquid crystals (Fig. 16) [66]. 

Along with the prediction and discovery of a macroscopic dipole in the SmC phase and the invention of ferroelectric liquid crystals in the SSFLC system, the discovery of antiferroelectric liquid crystals stands as a key milestone in chiral smectic LC science. Antiferroelectric switching (see below) was first reported for unichiral 4-[(l-methylheptyloxy)carbonyl]phenyl-4/-octyloxy-4-biphenyl carboxylate [MHPOBC, (3)],16 with structure and phase sequence... 

Figure 8.17 Structure and phase sequence of first banana-phase mesogen, reported by Vorlander in 1929, is given. Liquid crystal phase exhibited by this material (actually Vorlander s original sample) was shown by Pelzl et al.36a to have B6 stmeture, illustrated on right, in 2001. Achiral B6 phase does not switch in response to applied fields in way that can be said to be either ferroelectric or antiferroelectric.

There are two possibilities for the detection of the interferences the film detection and the registration of x-ray counts with scintillation counters or position-sensitive detectors. However, the SAXD method does not detect interferences from which the interlayer spacings can be calculated. It rather makes it possible from the sequence of the interferences to decide the type of liquid crystal [13,14]. 

The sequence of the interferences for the different liquid crystals is as follows ... 

A compound that has two immiscible hydrophilic and hydrophobic parts within the same molecule is called an amphiphilic molecule (as mentioned earlier). Many amphiphilic molecules show lyotropic liquid-crystalline phase sequences, depending on the volume balances between the hydrophilic part and the hydrophobic part. These structures are formed through the microphase segregation of two incompatible components on a nanometer scale. Hand soap is an everyday example of a lyotropic liquid crystal (80% soap + 20% water). 

The most important factor in zeolite synthesis in the laboratory, or factory, is the rate of crystallization. Composition and concentration of the liquid solution acting on the solids is important to the process as is the absolute necessity of maximum disorder of the Si-O-Al bonds in the initial solids reacted (Zhdanov, 1970). It is thus evident that not only bulk chemical (equilibrium) factors are important in the initial crystallization of zeolites but also the. relative free energies of the reactants. It is apparent that zeolite equilibria are essentially aqueous i.e., that silicate equilibrium or approach to it is attained through reaction with solutions, and thus the solubilities of the solids present are of primary importance. If materials are slow to enter into solution they are essentially bypassed in the rapid crystallization sequence (Schwochow and Heinze, 1970 Aiello, et al , 1970). In most studies the zeolites precipitated from solution appear to respond to the laws concerning chemical activity of solutions (Zhdanov, 1970). 

Prasang C, Whitwood AC, Bruce DW (2008) Spontaneous symmetry-breaking in halogen-bonded, bent-core liquid crystals observation of a chemically driven Iso-N-N phase sequence. Chem Commun 2008 2137-2139... 

The picture of consequent SB in condensed matter by cooling is illustrated in Fig. 3. Each SB has its own independent coordinate Q, and only the temperature scale is in common. The temperatures of SB are indicated by orders of magnitude, while their sequence is self-explanatory atoms => molecules => liquid => crystal(I) => crystal(II) => and so on. 

The smectic state, apart from exhibiting a rich variety of modifications, is also thermodynamically ordered. Thus, there is a well-defined sequence of phases formed on cooling from the isotropic liquid. For instance, the following transition sequence would be observed for a ferrocene liquid crystal exhibiting enantiotropic smectic C, smectic A and nematic phases ... 

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