Mixtures dynamic scattering

Sensitized for blue-green or red light, photoconductive polyimides and liquid crystal mixtures of cyanobiphenyls and azoxybenzene have been used in spatial light modulators [255-261]. Modulation procedure was achieved by means of the electrically controlled birefringence, optical activity, cholesteric-nematic phase transition, dynamic scattering and light scattering in polymer-dispersed liquid crystals. 

Akcasu AZ. Dynamic scattering from multicomponent polymer mixtures in solution and in bulk. In Brown W, ed. Dynamic Light Scattering The Method and Some Applications. Oxford Clarendon, 1993 1-75. 

Akcasu AZ, Nagele G, Klein R. Identification of modes in dynamic scattering from ternary polymer mixtures and interdiffusion. Macromolecules 1991 24 4408-4422. 

Akcasu et al. [74] attempted to identify the fast and slow modes with the two modes observed in dynamic scattering experiments from ternary polymer solutions. They defined the vacancies as the third component in a mixture of A and B polymers and concluded that the slow mode was obtained when vacancies were gradually removed, resulting in an incompressible binary mixture of A and B. The fast mode was obtained in the opposite limit of high vacancy concentration or a matrix with very high mobility. Since the polymer mobility and the vacancy concentration are small below, and high above, Tg, this suggested that the slow and fast-mode theories described interdiffusion below and above Tg, respectively. 

Finally, we remember that the Kapustin-Williams domains take place due to the effect of the positive conductive anisotropy of the nematic liquid crystal cr /a and disappear in the region or /a < 0 (Fig. 5.7(a)). The considerable decrease in the threshold voltage of the Kapustin-Williams domains for the large conductive anisotropy c7 /(jj proved to be a useful tool for developing liquid crystal mixtures for a dynamic scattering display with low controlling voltages [56]. 

Chevrons, inertial domains (Table 5.1), and light dynamic scattering which were discussed were also observed in mixtures of polymers with low molecular mass nematics [118]. 

Data Sheets on dynamic scattering mesogens and mixtures from E. Merck (Germany), Hoffman La Roche (Switzerland), American Liquid Crystal Company (Cleveland, U.S.A.), Chisso (Japan), etc. A. M. Lackner, J. D. Margerum, Mol. Cryst. Liq. Cryst. 1985,122, 111 S. E. Petrie, H. K. Bucher, R. T. Klingbiel, P. I. Rose, Eastman Org. Chem. Bull. 1973,45, 2. 

Dielectric anisotropy is an additive molar property. Thus, a small amount of PEBAB [Ae 10] (about 10-15 mol %) dissolved in MBBA [Ac —0.2] will provide a material suitable for twisted nematic devices. The threshold will, of course, be higher for this mixture than for a pure positive one such as 4-pentyl-4 -cyanobiphenyl, where the dielectric anisotropy is much higher. There are other influences on the threshold voltage for liquid crystal cells, principally the materials elastic constants and, in the case of dynamic scattering, material viscosity. The response times also are dependent upon elastic constants, viscosity, and dielectric anisotropy. These factors are discussed at length in a review by Goodman." ... 

M. Benmouna, H. Benoit, M. Duval, and Z. Akcasu. Theory of dynamic scattering from ternary mixtures of two homopolymers and a solvent. Macromolecules, 20 (1987), 1107-1112. 

M. Benmouna, M. Duval, and R. Borsali. Dynamic scattering from mixtures of homopolymers and copolymers in solution. Macromolecules, 21 (1987), 520-521. 

Figure 10.18 Dynamic light scattering (DLS) of vesicle mixtures, (a) P-index phase diagram and (b) size distributions (from DLS) for DDAB-oleate mixtures, total concentration 1 mM in 0.2 M borate buffer at pH 8.5, 25.0 °C, scattering angle 90°. (From Thomas and Luisi, 2004.)...

Nash, W., Pinder, D.N., Hernar, Y., Singh, H. (2002). Dynamic light scattering investigation of sodium caseinate and xanthan mixtures. International Journal of Biological Macromolecules, 30, 269-271. 

Even the traditional methods discussed in this chapter can be used for concentrated dispersions through contrast matching. For example, silica particles coated with silane coupling agents in a refractive index-matched mixture of ethanol and toluene can be used in combination with visible probe particles to study the dynamics of particles in dense systems. In the case of microemulsions (Chapter 8), selective deuteration of a component (oil, water, or surfactant) can be used in neutron scattering experiments even to measure the curvature of the oil-water interface. 

Measurements of static light or neutron scattering and of the turbidity of liquid mixtures provide information on the osmotic compressibility x and the correlation length of the critical fluctuations and, thus, on the exponents y and v. Owing to the exponent equality y = v(2 — ti) a 2v, data about y and v are essentially equivalent. In the classical case, y = 2v holds exactly. Dynamic light scattering yields the time correlation function of the concentration fluctuations which decays as exp(—Dk t), where k is the wave vector and D is the diffusion coefficient. Kawasaki s theory [103] then allows us to extract the correlation length, and hence the exponent v. 

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