Liquid crystal dispersions

Drzaic P S 1995 Liquid Crystal Dispersions (Singapore World Scientific)... 

Drzaic, P. S. Liquid Crystal Dispersions, World Scientific Singapore, 1995. 

Polymer-dispersed liquid crystals (PDLCs) are made up of nematic liquid crystals dispersed in a solid continuous polymer matrix. These are prepared by mixing a reactive monomer into a non-polymerisable LC medium and then polymerising the reactive monomer to create a polymer matrix, at the same time capturing the LCs as dispersed droplets, greater than 1 pm in diameter, i.e. the wavelength of visible light.3 -33... 

It also demonstrates that in both cases a similar reflectance vs temperature curve exists. In the region of the liquid crystal dispersion, i.e. between 20°C and 40°C, the oil removal increases significantly. Above the phase transition W + La — W + L3, between 40°C and 70°C, no further increase in oil removal takes place. For olive oil, a small decrease in detergent performance is observed. The interfacial tensions between aqueous solutions of C12E3 and mineral oil lie at about 5 mN m 1 at 30°C and 50°C and these relatively high values indicate that, in this system, the interfacial activity is not the decisive factor in oil removal from fabrics. 

As salinity was increased toward optimum, the formation of a permanent brine layer between the liquid crystal dispersion and microemulsion occurred. For the PDM system, the layer was stable except for some penetration by small projections of surface liquid crystal. No noticeable buildup of liquid crystal occurred at the dispersion boundary. 

The formation of a dispersion front can be described in terms of the diffusion path. As oil diffuses into the liquid crystal dispersion, the continuous phase gradually increases in oil content from an initial composition which would ordinarily be called a micellar solution to compositions which would be called... 

Arguably the most important parameter for any surfactant is the CMC value. This is because below this concentration the monomer level increases as more is dissolved, and hence the surfactant chemical potential (activity) also increases. Above the CMC, the monomer concentration and surfactant chemical potential are approximately constant, so surfactant absorption at interfaces and interfacial tensions show only small changes with composition under most conditions. For liquid crystal researchers, the CMC is the concentration at which the building blocks (micelles) of soluble surfactant mesophases appear. Moreover, with partially soluble surfactants it is the lowest concentration at which a liquid crystal dispersion in water appears. Fortunately there are well-established simple rules which describe how CMC values vary with chain length for linear, monoalkyl surfactants. From these, and a library of measured CMC values (35-38), it is possible to estimate the approximate CMC for branched alkyl chain and di- (or multi-) alkyl surfactants. Thus, most materials are covered. This includes the gemini surfactants, a new fashionable group where two conventional surfactant molecules are linked by a hydrophobic spacer of variable length (38). 

P. S. Drzaic, Liquid crystal dispersions, (World Scientific, NJ, 1995). 

Drzaic Paul S. Liquid Crystal Dispersion. Singapore World Scientific, 1995. 

Techniques for Obtaining Liquid Crystals Dispersed into a Polymeric Matrix... 

J. W. Doane, G. Chidichimo, and N. A. Vaz, Light modulating material comprising a liquid crystal dispersion in a plastic matrix, US Patent 4688900, assigned to Kent State University (August 25,1987). 

Figure 8.17 Theoretical diagram of structures which may occur in emulsions (viewed between crossed polars) (a) frozen liquid crystal (b) L2 phase (c) oil globule (d) gel network of frozen liquid crystal dispersed in phase (e) crystal in globule (b and d not visible in light microscope). From Barry [93] with permission.

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