Isotropic-smectic

The best known low molar mass substances forming cholesteric phases are esters of cholesterol, which are responsible for the name cholesteric phase. Therefore it was straightforward to attach these derivatives to a polymer in order to obtain cholesteric polymers. These experiments, however, failed because in all cases not cholesteric but isotropic, smectic or crystalline polymers resulted 22) (refer also to Shibaev and Plate, this issue). 

As a consequence of the alignment of solute molecules in liquid-crystalline solvents, the ratio of products formed in competitive reaction pathways can be different from that observed in isotropic liquids. This is illustrated by the Norrish type II photolysis of alkyl phenyl ketones with varying alkyl chain length in the isotropic, smectic, and... 

Another illustrative example is the photodrmerization of -octadecyl trans-cinnamate, which has been studied in the isotropic, smectic, and crystalline phases of n-butyl stearate, BS [731] cf. Eq. (5-165). 

AMORPHOUS, OPTICALLY ISOTROPIC MESOPHASE OF CHIRAL SIDE-CHAIN POLYMERS WITH A HIDDEN LAYER STRUCTURE—THE ISOTROPIC SMECTIC PHASE... 

We should state that our suggested model is not completely justified yet, but it remains the only one that can explain the whole ensemble of properties observed for the isotropic smectic phase of P8 M and related polymers. Keeping that in mind, we will refer hereafter to the mesophase as the isoSm phase, which most probably has the uitrashort pitch TGB A structure. 

The chiral side chain polymers derived from asymmetric esters of terephthalic acid and hydroquinone can form (in a broad temperature range, including ambient temperature) an unusual mesophase (the isotropic smectic phase, IsoSm ) characterized by high transparency and optical isotropy within the visible wavelength range, combined with a hidden layered smectic ordering and some elements of helical superstructure at shorter dimensions of 10 to 250 nm. The short-pitch TGB A model seems to be the most adequate for the mesophase structure. 

Kilian, D., Kozlovsky, M. V., and Haase, W. Dielectric measurements on the isotropic smectic phase of dyed side-chain polymers. Liquid Crystals 26, 705 (1999). 

Kozlovsky, M. V., Meier, J. G., and Stumpe, J. Chiral side-chain copolymers. 4. Kinetics of the phase transition from conventional isotropic liquid to the TGB-like isotropic smectic state. Macromol. Chem. Phys. 201, 2377 (20()0). 

The Effect of Polymer Heterogeneity on the Enthalpy. The kinetics of the isotropic-smectic phase transition were studied for two of the polymers HPX-C9 and HPX-C11, and in Figure 8 a summary of the calorimetric data for the former is presented. The behaviour of the HPX-C11 polymer was similar. Two processes are in fact revealed by these data (a) at high temperatures (7 471.9 K) the two processes have approximately the same induction time and rate and are therefore not resolved, (b) at intermediate temperatures (468.9heat evolved in the slower process is 30-50% of that evolved in the more rapid process. There is a tendency for an increase in Ah0 for the slow process with increasing temperature for HPX-C9, Ah0 was equal to 13 kJ/kg at 468.9 K and 20kJ/kg at 470.9 K. The same trend was observed for HPX-C11. (c) at low temperatures (TS467.9 K), the slower process was much retarded and not observed within the experimental window. 

The Norrish IIF/C product ratios from photolysis of a series of "alkylphenones (1) in the isotropic, smectic, and solid phases of BS shows significant phase dependence only for ketones... 

The dimers of benzoic and cinnamic acid were probably the first hydrogen-bonded liquid crystals [16], Since this report early in the 20th century, a wide variety of aromatic acid dimers such as 55 have provided information on the structure and properties of liquid crystals [125-127], A notable example is compound 56 which shows an optically isotropic smectic D phase [127],... 

P8 M is not the only polymer forming the isotropic smectic phase. To date, we have observed formation of that phase for a half-dozen chiral polymethacrylates and polysiloxanes. Table 5.1 summarizes the chemical structure and phase behavior of synthesized side-chain homopolymers, which carry chirally substituted side chains derived from asymmetric esters of terephthalic acid and hydroquinone. Such a structure with alternating orientation of carboxylic link groups seems to favour the formation of the IsoSm phase, whereas isomeric derivatives of p-hydroxybenzoic acid, where all carboxylic links have the same orientation, form only conventional Sm A and Sm C phases. Molar mass of all the synthesized homo- and copoly(meth)acrylates is within the range of 1 to 2-10 g mol the poiysilox-anes have the average degree of polymerization, p 35. 

Amorphous, Optically Isotropic Mesophase of Chiral Side-Chain Polymers with a Hidden Layer Structure— The Isotropic Smectic Phase 148... 

Fig. 2.7.4. The measured X-ray reflectivity from the free surface of the isotropic phase of 12CB at temperatures very close to the isotropic-smectic A transition point. The step-like form of the intensity curve reveals the quantized nature of the layer growth at the surface. (After Ocko et...

AFM Force Spectroscopy Near Isotropic-Nematic and the Isotropic-Smectic Phase Tansitions... 

The pre-smectic interaction is therefore observable already in the isotropic phase, although there is no direct phase transition from the isotropic to the smectic-A phase in 8CB. This makes the capillary condensation of the smectic-A phai in the gap between the surfaces impossible and consequently enables more detailed observation of the presmectic interaction. In the case when there is a direct isotropic-smectic-A phase transition, like for example in 12CB, a condensation phenomenon similar to nematic capillary condensation is observable. 

Ellipsometry of the Glass-Isotropic Smectic Liquid Crystal Interface... 

The smectic layering transition [45] is a phenomenon, where smectic layers grow one by one, parallel to the surface, when the temperature approaches the isotropic-smectic phase transition from above. Ellipsometric observation of these steps is possible due to the coupling between the smectic order and the nematic (orientational) ordering. Consequently, the orientational order in... 

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