Cholesteric blue liquid crystalline phases

There is ample evidence that small cycloalkanes and many of their derivatives with similar sphere-like shapes can exist as plastic crystals [21,22]. They are not birefringent and exhibit fewer X-ray diffraction lines in the plastic phases than in the corresponding (lower temperature) normal crystalline phases. Many plastic phases have cubic lattices like those of the closely related smectic D phases [33] which are comprised of aggregates of rod-like molecules. In both cases, more than one molecule can constitute the unit cell or fundamental lattice unit so that several molecules may tumble in a correlated motion. A similar microscopic model explains the lack of optical birefringence in the related cholesteric blue liquid crystalline phases from some chiral... 

The structure of the blue phase is of some importance. Among the lipoproteins carrying lipids in the blood, low-density lipoproteins (LDL) have attracted much attention. They are the factors mainly responsible for plaque formation, which ultimately leads to atheriosclerotic changes and heart disease. The major components of the LDL-particles are cholesterol fatty acid esters. A remarlmble property is the constant size of LDL particles [28], which indicates that the interior must possess some degree of order. It seems probable that the structure proposed above for cholesterol esters in the cholesteric liquid-crystalline structure should occur also in the LDL-particle. In that case the LDL particle can be viewed as a dispersed blue phase, whose size is related to the periodicity of the liquid-crystalline phase, and the protein coat at the surface is oriented parallel to adjacent specific crystallographic planes of the blue phase. These amphiphilic proteins will expose lipophilic segments inwards emd expose hydrophilic groups towards tiie enviroiunent. 

L-glucose enantiomer (Figure 5.38). Correspondingly, the green cholesteric liquid crystalline phase becomes red upon addition of D-glucose and blue upon addition of L-glucose. Diasteromeric hexoses gave similar effects. ... 

A cholesteric phase represents a special case of a nematic phase. The planes of adjacent molecules are also parallel, but the longitudinal axis of adjacent planes are turned about a definite angle. The result is a screw structure of the system. Cholesteric thermotropic liquid crystalline phthalocyanines are also known. ( + )-2,3,9,10,16,17,23,24-octakis[4-(dodecyloxy)-2-oxapentyl]phthalo-cyanine (preparation see Schemes 13 and 14) shows a texture typical for cholesteric phases [155], At 160°C, this compound gives a fluid isotropic phase. Upon cooling an anisotropic phase appears at 153 °C. The texture similar to platelets (blue phase) changes at 66 °C to typical cholesteric fan-shape structure and remains fan-shaped down to room temperature. Except for the discotic... 

The concept of defects came about from crystallography. Defects are dismptions of ideal crystal lattice such as vacancies (point defects) or dislocations (linear defects). In numerous liquid crystalline phases, there is variety of defects and many of them are not observed in the solid crystals. A study of defects in liquid crystals is very important from both the academic and practical points of view [7,8]. Defects in liquid crystals are very useful for (i) identification of different phases by microscopic observation of the characteristic defects (ii) study of the elastic properties by observation of defect interactions (iii) understanding of the three-dimensional periodic structures (e.g., the blue phase in cholesterics) using a new concept of lattices of defects (iv) modelling of fundamental physical phenomena such as magnetic monopoles, interaction of quarks, etc. In the optical technology, defects usually play the detrimental role examples are defect walls in the twist nematic cells, shock instability in ferroelectric smectics, Grandjean disclinations in cholesteric cells used in dye microlasers, etc. However, more recently, defect structures find their applications in three-dimensional photonic crystals (e.g. blue phases), the bistable displays and smart memory cards. 

For facilitating the survey of the numerous publications concerning phase transitions the latter are classified by the method of examination. The letter after the reference gives the types of the liquid crystalline phases which are involved in the transitions investigated. The different smectic phases are all listed under the symbol S if only transitions between smectic phases were observed see letter k. In the cases of twisted-grainboundary phases (TGB), cholesteric phases (N ) and blue phases (BP) their symbols are positioned beside the reference number of the literature and the referring letter. The letters mean the following combinations of phase transitions (a) N-I (b) S-I (c) S-N-I (d) Cr-N-I (e) Cr-S-I (f) Cr-S-N-I (g) S-N (h) Cr-N (i) Cr-S-N (j) Cr-S (k) S-S. 

The strange blue phase liquid-crystalline condition of certain cholesteryl esters (nonanoate and myristate) exists over a very narrow temperature range between the cholesteric and isotropic phases. Its structure has now been probed by study of deuterium-labelled materials. The H n.m.r. spectra have been inter-... 

The blue phase was earlier classified as belonging to the cholesteric phase, but is in fact a separate phase. It is in a sense a crystalline liquid. The molecules are positionally disordered and have no fixed mean positions, but the spatial pattern of molecular orientations can be assigned to a translation group. Usually the blue phase falls between the cholesteric and the isotropic phase, but direct transition to the smectic phase has been observed. Three blue phases have been found, one of them is amorphous. 

Emoto A, Uchida E, Fukuda T (2012) Optical and physical applications of photocontrollable materials azobenzene-containing and liquid crystalline polymers. Polymers 4 150-186 Ericson LM, Fan H, Peng HQ, Davis VA, Zhou W, Sulpizio J, Wang Y, Booker R, Vavro J, Guthy C et al (2004) Macroscopic, neat, single-walled carbon nanotube fibers. Science 305 1447-1450 Etchegoin P (2000) Blue phases of cholesteric liquid crystals as thermotropic photonic crystals. Phys Rev E 62 1435-1437... 

Besides those phases mentioned above, many other phases of liquid crystals such as smectic G, H, I, F,...,Q,..., and cholesteric blue phase have been identi-fjed,2,7,8 name a few. Numerous new molecular engineered liquid crystalline... 

---