Blue phases temperature range

A similar effect occurs in highly chiral nematic Hquid crystals. In a narrow temperature range (seldom wider than 1°C) between the chiral nematic phase and the isotropic Hquid phase, up to three phases are stable in which a cubic lattice of defects (where the director is not defined) exist in a compHcated, orientationaHy ordered twisted stmcture (11). Again, the introduction of these defects allows the bulk of the Hquid crystal to adopt a chiral stmcture which is energetically more favorable than both the chiral nematic and isotropic phases. The distance between defects is hundreds of nanometers, so these phases reflect light just as crystals reflect x-rays. They are called the blue phases because the first phases of this type observed reflected light in the blue part of the spectmm. The arrangement of defects possesses body-centered cubic symmetry for one blue phase, simple cubic symmetry for another blue phase, and seems to be amorphous for a third blue phase. 

When the disperse phase has a slightly higher refractive index the compound tends to be blue when it is lower than that of the PVC the compound tends to be yellow and hazy. In order to overcome this a carefully determined quantity of a second MBS additive, with an appropriate refractive index and whieh is compatible with the PVC compound and hence forms a continuous phase with it, may be added to match the refractive indices. Such a matching operation should be evaluated at the proposed serviee temperature range of the product since the temperature coefficients of the two phases are usually different and a film which is blue at proeessing temperature may become yellow at 20°C. 

Note 3 With chiral nematic substances forming chiral nematic mesophases of short pitch (<700 nm), up to three blue phases occur in a narrow temperature range between the chiral nematic phase and the isotropic phase. 

In the past, blue phases largely remained a subject of scientific curiosity, because for many years the rather limited temperature range (commonly from 0.5 to 2°C) severely restricted further scientific exploration as well as practical use of these intriguing phases. Early work on blue phases primarily focused on new materials [379-392], their response to electric fields [393 -06], the shape of blue phase crystals grown for example under an applied electric field [407 -09], as well as lasing in blue phases [410]. 

It was really only a matter of time until researchers in the field started doping blue phases with quasi-spherical nanoparticles. This area is very much in its infancy, but the few recent reports already show some promising results. Yoshida et al., for example, reported on an expansion of the temperature range of cholesteric blue phases from 0.5 to 5°C by doping blue phases with gold nanoparticles (average diameter of 3.7nm) as well as a decrease in the clearing point of approximately 13°C [427]. A similar effect was also observed by Kutnjak et al. for CdSe quantum dots simultaneously capped with oleyl amine and TOP (diameter of the core 3.5 nm) in CE8 (Merck) and CE6 (BDH). The authors found that particularly blue phase III was stabilized in these mixtures, blue phase II destabilized, and... 

Expanding the Stable Temperature Range of Blue Phases. 109... 

Early studies on blue phase were assuredly marked by one astonishing discovery after another, such as the narrow stable temperature range, optical isotropy, three-dimensional order, and frustration. These unique characteristics, not observed in any other liquid crystal phases, have enthralled these pioneering researchers, as is obvious from their writings. 

Fig. 12 Chemical structure of T-shaped dimeric liquid crystal molecules that broadened the temperature range of blue phases to 13 K [24]...

Technologies to expand the narrow temperature range of blue phases have thus been in rapid development in recent years. At last, it seems that we have arrived at the dawn of an era in which real progress will be made towards realizing practical applications of blue phases. 

New chiral phases, called smectic blue phases (BPSm), have been discovered in a small temperature range with the following phase sequence TGB-BPsml-BPsm2-BPsm3-Iso, without any intermediate chiral nematic phase between the BPSm and TGB phases [27,28]. X-ray scattering studies showed that unlike the traditional blue phases, the smectic blue phases possess the quasi-long-range smectic order in addition to three-dimensional orienta-... 

Figure 8.8 Principle of the PIT method an o/w-emulsion changes into a w/o-emulsion above a certain temperature. In the phase inversion range a microemulsion develops, which becomes a blue o/w-emulsion after cooling down. (From Ref. [48], reprinted with permission of Elsevier.)...

Some cholesteric materials show the blue phase as the temperature increases from that of the cholesteric phase and before it reaches that of the isotropic phase. The blue phase is a cubic phase. There have been three blue phases found so far BP I, BP II and BP III phases. It is now understood that the BP I phase is a body-centered cubic, the BP II phase is a primitive cubic and the BP III phase is a fog phase with no structural symmetry. Generally the temperature range of the blue phase is quite narrow, less than 1 degree... 

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 phases occur in cholesteric systems of sufficiently low pitch, less than about 5000 A. They exist over a narrow temperature range, usually 1 C, between the cholesteric liquid crystal phase and the isotropic liquid phase (see (1.3.5)). The first observation of a blue phase was described by Reinitzer himself in his historic letter to Lehmann as follows On cooling (the liquid phase of cholesteryl benzoate) a violet and blue phenomenon appears, which then quickly disappears leaving the substance cloudy but still liquid. Although Lehmann recognized it as a stable phase, not until the 1970s was it generally accepted that the blue phases are thermodynamically distinct phases. The nature of these phases has now become a subject of considerable interest to condensed matter physicists. 

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