Smectic state

Note 1 In the equation for g, the term go is usually equal to zero because the undistorted state of nematics is the state of uniform alignment. However, for chiral nematics, a nonzero value of go allows for the intrinsic twist in the structure. In order to describe g for smectic phases, an additional term must be added, due to the partially solid-like character of the smectic state and arising from positional molecular deformations. 

Starkweather, H. W. A comparison of the rheological properties of polytetrafluoroethylene below its melting point with certain low-molecular weight smectic states. J. Polymer Sci., Polymer Phys. Ed. 17, 73 (1979)... 

Fig. 33. The temperature dependence of the orientational order parameter S of the copolymer No. 4 of Table 8 in the cholesteric and smectic state. (T = T /Tm T = clearing temperature, Tm = measuring temperature)...

Solid -> smectic1 91°C A/ofe This compound exhibits two stable smectic states... 

R The chromophores of vision when in the precipitated smectic state exhibit both their normal intrinsic spectral... 

According to Oseen, the smectic state corresponds to the vanishing of all the moduli except k22 and 33 (our notation). The (free) energy is then minimized when... 

Before leaving the subject of the smectic state, we may remark that to explain deformations in which the area of individual molecular layers does not remain constant, it is necessary to invoke dislocations of these layers. It is likely that these dislocations are usually combined with the focal conic singularity lines, being then essentially screw dislocations. 

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 ... 

Unaligned, disrupted smectics, such as those prepared by quenching from an elevated temperature into the smectic state, are frequently filled with focal conic domains (Sethna and Kleman 1982 Lavrentovich 1986 Larson and Mather 1997). Parabolic focal conic domains can be packed to fill space as shown in Fig. 10-30a. Another packing, which... 

Figure 1 Schematic view of the amylopectin molecule in the dry (nematic) and hydrated (smectic) states the double helices are represented as the block like mesogens...

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). 

Among the various cholesterol derivatives the oleyl ester COC and nonanoate CN are common. Octyloxy biphenyle (M24), which melts at 54.5°C in the smectic state, turns nematic at 67°C and isotropic at 80°C, is considered as a typical smectic compound, as well as its eutectic mixture,, with nonyloxy CB (M27). The currently used LC, constituants of the mixtures employed in the text, are listed in Table II. ... 

Continued investigations led to the identification of three main types of mesophase a smectic state smegma in Greek, meaning soap), a nematic state nema in Greek, meaning thread), and a cholesteric state observed in systrans containing molecules with a chiral craitCT. 

Analogous ochre-yellow polymers 4.26 that contain thiophene in the main chain (Mw= 11,300-35,300 PDI = 1.5-2.7) have also been prepared [61]. Upon slow concentration of their solutions in chlorinated solvents, such as chloroform, lyotropic nematic liquid-crystalline phases form. In one case, a lyotropic smectic state was identified. 

A number of different smectic states exist among the low molecular weight mesomorphic compounds. The molecules, for example, might be normal to the planes or tilted relative to the normal. The different states have been given various letter designations (Smectic A, B, C etc.) and deVries (2) has classified the x-ray patterns obtained from the various types of smectic (and also nematic) states. 

The decrease in the melting and/or clearing points of the monomers caused by the presence of the polymer was detected in both the smectic state polymerization of vinyl oleate (l8,19) and in the polymerization of cholesterylacrylate in the cholesteric state (ij). The polyvinyl oleate formed in this reaction was crystalline while the polycholesterylacrylate was amorphous. The temperat ore of the phase transition was reduced in both cases. 

In our present work the mesomorphic state polymerization was investigated from the point of view of solid-state polymerization. The thermodynamic interactions of monomers and polymers can he represented hy state diagrams. Effects reported hy Sadron et al. may only he expected in the homogeneous areas of the state diagrams. The thermodynamic conditions leading to such areas are fulfilled frequently in smectic states hut rarely in cholesteric or nematic ones. 

Frame II from Fig. 2b pictures the development of the smectic phase from the nematic state. The benzene rings are in the smectic state arranged in planes perpendicular to the draw direction, whereas the lateral packing of neighbouring molecules shows no positional order. The smectic phase could be attained through an increase in the mobility of the molecular segments lead-... 

Finally, there is some indication that polymers with mesogenic moieties and flexible spacers in the main chain may also form smectic phases which exhibit 3 D-order. The X-ray diffraction patterns of poly (p,p -benzylidene aminophenylsebacate) and poly-diphenyl sebac ate) in the smectic state were characterized by a sharp central ring and a sharp outer ring which indicates a periodic order within the lamellae. Such results are typical features of... 

---