Light scattering liquids

Fig. 8 Photographs of light scattering liquid crystal cells filled with a gel consisting of 5CB and ZI3I2 (a) light scattering state (electric field off) (b) light transmission state (electric field on)...

In the next section we discuss linear hydrodynamics and its role in understanding the inelastic light scattering experiments from liquids, by calculating the density-density correlation fiinction,. Spp. 

Schaetzing R and Ulster J D 1979 Light scattering studies of liquid crystals Advances in Liquid Crystais vol4 (London Academic)... 

Next let us consider the light scattered by liquids of low molecular weight compounds. We are actually not directly interested in this quantity per se, but in scattering by solutions-polymer solutions eventually, but for now solutions of small solute molecules. The solvent in such a solution does scatter, but, in practice, the intensity of light scattered by pure solvent is measured and subtracted as a blank correction from the scattering by the solution. 

The first thing to realize about scattering by liquids is that individual molecules can no longer be viewed as independent scatterers. If a liquid were perfectly uniform in density at the molecular level, its molecules could always be paired in such a way that the light scattered by each member of a pair would be exactly out of phase with the other, resulting in destructive interference. No net scattering results in this case. The second thing to realize, however, is that density is not perfectly uniform at the molecular level. 

Light Scattering by Liquid Surfaces and Complementary Techniques, edited by Dominique Langevin... 

Rayleigh s results do not apply fully to solutions. He had assumed that each particle acted as a point source independent of all others, which is equivalent to assuming that the relative positions of the particles are random. This is true in the gases with which he worked, but is not true in liquids. Hence, for solutions, the scattered light is less intense by a factor of about 50 due to interference of the light scattering from different particles. 

With the development of new instrumental techniques, much new information on the size and shape of aqueous micelles has become available. The inceptive description of the micelle as a spherical agglomerate of 20-100 monomers, 12-30 in radius (JJ, with a liquid hydrocarbon interior, has been considerably refined in recent years by spectroscopic (e.g. nmr, fluorescence decay, quasielastic light-scattering), hydrodynamic (e.g. viscometry, centrifugation) and classical light-scattering and osmometry studies. From these investigations have developed plausible descriptions of the thermodynamic and kinetic states of micellar micro-environments, as well as an appreciation of the plurality of micelle size and shape. 

Dynamic surface tension has also been measured by quasielastic light scattering (QELS) from interfacial capillary waves [30]. It was shown that QELS gives the same result for the surface tension as the traditional Wilhelmy plate method down to the molecular area of 70 A. QELS has recently utilized in the study of adsorption dynamics of phospholipids on water-1,2-DCE, water-nitrobenzene and water-tetrachloromethane interfaces [31]. This technique is still in its infancy in liquid-liquid systems and its true power is to be shown in the near future. 

Lafosse, M., Dreux, M., Morin-Allory, L., and Colin, J. M., Some applications of a commercial light-scattering detector for liquid chromatography, J. HRC CC, 8, 39, 1985. 

Mourey, T. H. and Oppenheimer, L. H., Principles of operation of an evaporative light-scattering detector for liquid chromatography, Anal. Chem., 56, 2427, 1984. 

---