Smectic M phase

The positional order of the molecules within the smectic layers disappears when the smectic B phase is heated to the smectic A phase. Likewise, the one-dimensional positional order of the smectic M phase is lost in the transition to the nematic phase. AH of the transitions given in this example are reversible upon heating and cooling they are therefore enantiotropic. When a given Hquid crystal phase can only be obtained by changing the temperature in one direction (ie, the mesophase occurs below the soHd to isotropic Hquid transition due to supercooling), then it is monotropic. An example of this is the smectic A phase of cholesteryl nonanoate [1182-66-7] (4), which occurs only if the chiral nematic phase is cooled (21). The transitions are aH reversible as long as crystals of the soHd phase do not form. 

There are the smectic B, F and I phases belonging to this kind of liquid crystal, the so-called hexatic phase. The newly discovered smectic M phase is also catalogued to the hexatic liquid crystal phase. These hexatic phases have a six-fold symmetry which can be observed from the X-ray scattering intensity at q = 2n/a. 

The smectic M phase, discovered in 1990, may be classified as a hexatic phase. The molecules are tilted within layers but are not miscible with the Sp and Si phases. The structural details are under investigation. 

Detailed x-ray diffraction studies on polar liquid crystals have demonstrated tire existence of multiple smectic A and smectic C phases [M, 15 and 16]. The first evidence for a smectic A-smectic A phase transition was provided by tire optical microscopy observations of Sigaud etal [17] on binary mixtures of two smectogens. Different stmctures exist due to tire competing effects of dipolar interactions (which can lead to alternating head-tail or interdigitated stmctures) and steric effects (which lead to a layer period equal to tire molecular lengtli). These... 

Fig. 7. Snapshots from a smectic-A phase of liquid crystal dimer molecules composed of two Gay-Berne mesogens linked by a flexible alkyl chain. Data from [112] supplied by Dr M R Wilson, University of Durham...

Cr Cub, Cubv d E G HT Iso Isore l LamN LaniSm/col Lamsm/dis LC LT M N/N Rp Rh Rsi SmA Crystalline solid Spheroidic (micellar) cubic phase Bicontinuous cubic phase Layer periodicity Crystalline E phase Glassy state High temperature phase Isotropic liquid Re-entrant isotropic phase Molecular length Laminated nematic phase Correlated laminated smectic phase Non-correlated laminated smectic phase Liquid crystal/Liquid crystalline Low temperature phase Unknown mesophase Nematic phase/Chiral nematic Phase Perfluoroalkyl chain Alkyl chain Carbosilane chain Smectic A phase (nontilted smectic phase)... 

Gorecka E, Nakata M, Mieczkowski J, Takanishi Y, Ishikawa K, Watanabe J, Takezoe H, Eichhorm SH, Swager TM (2000) Induced antiferroelectric smectic-CA phase by doping ferroelectric-C phase with bent-shaped molecules. Phys Rev Lett 85 2526-2529... 

Kajitani T, Masu H, Kohmoto S, Yamamoto M, Yamaguchi K, Kishikawa K (2005) Generation of a chiral mesophase by achiral molecules absolute chiral induction in the smectic C phase of 4-octyloxyphenyl 4-octyloxybenzoate. J Am Chem Soc 127 1124-1125... 

Demikhov, E., Kozlovsky, M. V, Amorphous chiral smectic A phase of side-chain copolymers. Liquid Crystals 18, 911 (1995). 

When the number of alkylene spacers m was even (4 or 6) an enantiotropic smectic LC-phase was observed, whereas when m was odd only an isotropic melt was observed. According to the MI, an even value of m yields MI=9.5, while an odd value gives MI=9. 

Als-Nielsen J, Litster J D, Birgeneau R J, Kaplan M and Safinya C R 1980 Lower marginal dimensionality. X-ray scattering from the smectic-A phase of liquid crystals Ordering in Strongly Fluctuating Condensed Matter Systems ed T Riste (New York Plenum)... 

Leadbetter A J, Frost J C and Mazid M A 1979 Interlayer correlations in smectic B phases J. Physique Lett. 40 325-9... 

For compound 23 the uncharacterized phase, denoted as M, was found to be exhibited over a fairly wide temperature range. Ribeiro et al, found that the X-ray diffraction patterns associated with the intermediary phase were typical of a disordered smectic modification. The d spacing of 45.3 A was found to be a little bit shorter than the calculated molecular length which is consistent with the presence of a smectic A phase. As the material also exhibits a Grandjean plane texture it was concluded that the phase must be a TGB modification. However, the platelet/fan texture exhibited by the mesophase conversely suggests that a columnar ordering must be present as well,... 

Fig. 14. The dependence of the transition temperatures on the number of carbon atoms, m, in the terminal alkyl chain for the CB060.m series [68]. denotes nematic-isotropic transitions, O intercalated smectic A-nematic transitions, smectic-intercalated smectic A transitions, A interdigitated smectic A-interdigitated smectic C transitions and interdigitated smectic A-nematic transitions. The melting points have been omitted for the sake of clarity. SmA Interdigitated smectic A phase SmCa interdigitated smectic C phase SmA intercalated smectic A phase S unidentified smectic phase N nematic / isotropic...

Fig. 5.4.2. A rare example of a pair of singular lines, one almost straight and the other almost circular in a toric domain in the (a) smectic A and (h) smectic C phases. Additional disclination lines develop near the centre in the smectic C phase for reasons discussed in 5.8.3. (From A. Perez, M. Brunet and O. Parodi, J. de Physique Lettres, 39, 353 (1978)).

In the meantime, Ohta et studied the complete series of symmetric copper complexes ((53) M = Cu R = R = C H2 +i, = 0 to 14), which confirmed the previous results. The ligand showed a crystal smectic E phase from the octyl derivative onwards as determined by miscibility studies. The first four complexes ((53) M = Cu R = R = C H2 +i, = 0 to 3) were not mesomorphic, then a mono tropic phase was detected for = 4, which became enantiotropic for > 5. Moreover, for n = l and 8, the copper complexes showed an additional mesophase, while the nonyl derivative exhibited two additional mesophases. Crystalline structures of some tetra-alkyl copper, palladium, and nickel complexes of / -diketonates revealed that the flat molecular species were stacked into columns, the planes of the molecules forming a small tilt with respect to the columnar axis-these columns were further organized into layers. Variable-temperature and NMR ... 

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