Smectic light scattering

The ratio reaches up to one million times. This explains why the liquid crystal is in fact very turbid while ordinary liquid is transparent. The light scattering varies for different phases of the liquid crystals. For example, owing to the suppression of molecules into layers the light scattering of the smectic A phase is less than the nematic liquid crystal. For the smectic C phase, the fluctuation of the projection of tilted molecules onto smectic layers (the c-vector) causes stronger scattering than that in the smectic A phase. 

An important source of error in these calculations is the neglect of short-range order. In particular, the theory fails for the bend and twist elastic constants when smectic-like short-range order is present in the nematic liquid crystal. Under such circumstances these two constants exhibit a critical divergence as the temperature approaches the smectic-nematic point and the light scattering also shows a marked temperature dependence. The present treatment is then inadequate and more elaborate models have been proposed. The phenomenological theory of this aspect of the problem will be discussed in chapter 5. 

Fig. 5.5.2. Temperature dependence of the susceptibility Of) and the correlation lengths if and for smectic A short-range order in the nematic phase of butoxybenzylidene-octylaniline. Open circles were deduced from X-ray scattering, and filled circles from light scattering. The smectic density wavevector remains...

Fig. 5.8.4. Plot of versus from light scattering measurements in the smectic C phase of di(4-n-decyloxybenzal)-2-chloro-l-4-phenylene diamine. The wavevector q relative to the layers is indicated in the inset at the top left-hand comer. The experimental points lie on an ellipse as expected theoretically. However, the minor axis of the ellipse does not coincide exactly with the molecular axis, which is assumed to be inclined at 45 to the layer normal. (After Galerne et /. >)...

Fig. 11.12 Light scattering by the smectic A phase. Huctuating elastic modes in the z and x directions in a planar cell with director no II z (a) and typical geometry of scattering on fluctuating smectic layers (b)...

In this paper, the phase transition behavior, aggregation states, and also, a bistable and reversible light switching behavior based on light scattering have been investigated for the ternary (LCP/LC2/LC1) composite system in an induced smectic phase. 

R. G. Horn, ""Refractive indices and order parameters of two liquit crystals, J. Phys., vol. 39, pp. 105-109, 1978 W. Urbach, H Hervet, and F. Rondelez, ""Thermal diffusivity measurement in ne matic and smectic phases by forced Rayleigh light scattering, Mo lec. Cryst. Liq. Cryst., vol. 46. pp. 209-221, 1978. 

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