Liquid-crystal separation

The wide variety of the state diagrams of crystal and mixed (semicrystalline) equilibria for low-molecular compounds have been fully cx nsidered in the literature (Kogan, 1968 Shpil rain and Kassel man, 1977 Vol and Kagan, 1979). 

The thermodynamic stimulus for crystallization (liquid-crystal phase separation) is the equality of the chemical potentials of each component in the crystal phase G o,.cr and in the solution 6 , at a certain temperature Y l and concentration x,f. 

The absence of specific precrystallization phenomena in a one-component liquid is the subject of a number of papers (Skripov and Baydakov, 1972 Skripov, 1975). 

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Dihydroxylamino-manganous Chloride, [Mn(NH3OH),]Cl2, may be formed by treating a hot aqueous solution of manganous chloride with hydroxylamine hydrochloride and adding a further quantity of the base in alcohol. On cooling the liquid crystals separate. The substance is white and very stable, only beginning to decompose at 150° C.5... 

Figure 6.9. State diagram of the system PEO+water liquid-liquid separation- M = 5,000 (/), M = 3,000 (2) liquid-crystal separation—A/ = 5,000 ( f), M =. 3,000 ( ) (Malcolm et al., 1957) [Reprinted with permission from G.N.Malcolm, J.S.Rowlinson. TVans. Faraday Sor. 7(415) (19.57) 921-931. Copyright 1957 by the Royal Society of Chemistry]...

D. O. Shah and W. C. Hsieh, Microemulsions, Liquid Crystals and Enhanced Oil Recovery, in Theory, Practice, and Process Principles for Physical Separations, Engineering Foundation, New York, 1977. 

Chiral liquid crystals Chiral recognition Chiral separation Chiral separations Chiral shift reagents... 

A number of analytical methods have been developed for the determination of chlorotoluene mixtures by gas chromatography. These are used for determinations in environments such as air near industry (62) and soil (63). Liquid crystal stationary columns are more effective in separating m- and chlorotoluene than conventional columns (64). Prepacked columns are commercially available. ZeoHtes have been examined extensively as a means to separate chlorotoluene mixtures (see Molecularsieves). For example, a Y-type 2eohte containing sodium and copper has been used to separate y -chlorotoluene from its isomers by selective absorption (65). The presence of ben2ylic impurities in chlorotoluenes is determined by standard methods for hydroly2able chlorine. Proton (66) and carbon-13 chemical shifts, characteristic in absorption bands, and principal mass spectral peaks are available along with sources of reference spectra (67). 

However, conductive elastomers have only ca <10 of the conductivity of soHd metals. Also, the contact resistance of elastomers changes with time when they are compressed. Therefore, elastomers are not used where significant currents must be carried or when low or stable resistance is required. Typical apphcations, which require a high density of contacts and easy disassembly for servicing, include connection between Hquid crystal display panels (see Liquid crystals) and between printed circuit boards in watches. Another type of elastomeric contact has a nonconducting silicone mbber core around which is wrapped metalized contacts that are separated from each other by insulating areas (25). A newer material has closely spaced strings of small spherical metal particles in contact, or fine soHd wires, which are oriented in the elastomer so that electrical conduction occurs only in the Z direction (26). 

Liquid Crystal Third Phase. In addition to micelles and microemulsion droplets, surfactants may form Hquid crystals. A Hquid crystal is a separate phase, which comes out of solution, not like the micelles or microemulsion droplets, which are microscopic entities within the solution. 

Liquid crystals stabilize in several ways. The lamellar stmcture leads to a strong reduction of the van der Waals forces during the coalescence step. The mathematical treatment of this problem is fairly complex (28). A diagram of the van der Waals potential (Fig. 15) illustrates the phenomenon (29). Without the Hquid crystalline phase, coalescence takes place over a thin Hquid film in a distance range, where the slope of the van der Waals potential is steep, ie, there is a large van der Waals force. With the Hquid crystal present, coalescence takes place over a thick film and the slope of the van der Waals potential is small. In addition, the Hquid crystal is highly viscous, and two droplets separated by a viscous film of Hquid crystal with only a small compressive force exhibit stabiHty against coalescence. Finally, the network of Hquid crystalline leaflets (30) hinders the free mobiHty of the emulsion droplets. 

Similarly, different unit operations are available to accomplish the same processing objective. For example, a filter, a centrifuge, or a decanter could be used to separate a solid from a liquid. Crystallization or distillation could also be used for purification. 

It yields a well-defined phenyl-urethane, melting at 113°. It requires considerable care to obtain this compound, which should be prepared as follows terpineol mixed with the theoretical amount of phenyl-isocyanate is left for four days at the ordinary room temperature. Crystals separate which are diphenyl urea,, and are removed by treating the product with anhydrous ether, in which the diphenyl urea is insoluble. If the liquid be very carefully and slowly evaporated fine needles of terpinyl-phenyl urethane separate. This compound has the formula C Hj. NH. COOCjqHj-. The correspnanding naphthyl-urethane melts at 147° to 148°. 

A 7.7 mg portion of band 5 was taken up in a minimum of acetone and refrigerated until crystals separated. This cold acetone mixture was centrifuged and the supernatant liquid removed by pipette. To the remaining crystals, a few drops of ice-cold ether-acetone, three to one mixture, were added, shaken, recentrifuged and the supernatant wash liquid removed by pipette. The ether-acetone wash was repeated. The resulting crystals were dried under vacuum yielding 3.3 mg of pure compound F, 17-hvdroxycorticosterone. 

After cooling crystals separated from the remaining liquid are collected by filtration and re-crystallized from aqueous ethanol, whereby 2,5 parts by weight of 3-(2, 4, 5 -triethoxybenz-oyl]-propionic acid are obtained as colorless needles, melting point 150°C to 151 °C. 

Add 2.0 g of salicylic acid, 5.0 mL of acetic anhydride, and 5 drops of 85% H3P04 to a 50-mL Erlenmeyer flask. Heat in a water bath at 75°C for 15 minutes. Add cautiously 20 mL of water and transfer to an ice bath at 0°C. Scratch the inside of the flask with a stirring rod to initiate crystallization. Separate aspirin from the solid-liquid mixture by filtering through a Buchner funnel 10 cm in diameter. 

The anisotropy of the liquid crystal phases also means that the orientational distribution function for the intermolecular vector is of value in characterising the structure of the phase [22]. The distribution is clearly a function of both the angle, made by the intermolecular vector with the director and the separation, r, between the two molecules [23]. However, a simpler way in which to investigate the distribution of the intermolecular vector is via the distance dependent order parameters Pl+(J") defined as the averages of the even Legendre polynomials, PL(cosj r)- As with the molecular orientational order parameters those of low rank namely Pj(r) and P (r), prove to be the most useful for investigating the phase structure [22]. 

There have been several simulations of discotic liquid crystals based on hard ellipsoids [41], infinitely thin platelets [59, 60] and cut-spheres [40]. The Gay-Berne potential model was then used to simulate the behaviour of discotic systems by Emerson et al. [16] in order to introduce anisotropic attractive forces. In this model the scaled and shifted separation R (see Eq. 5) was given by... 

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