Dissymmetry light scattering

Apart from their utility in determining the correction factor 1/P( ), light-scattering dissymmetry measurements afford a measure of the dimensions of the randomly coiled polymer molecule in dilute solution. Thus the above analysis of measurements made at different angles yields the important ratio from which the root-mean-square... 

Value based on light-scattering dissymmetry for a fraction of molecular weight 220,000.22... 

Figure 18 Plot of light-scattering dissymmetry ratio [7(45°)//(135°) against concentration c for a polystyrene-i)/oc/c-poly(ethylene/propylene) (37000 59 700 M ) copolymer in decane at 30 °C. The experimental points are indicated by circles ( ). The full curve and squares ( ) indicates the behaviour predicted theoretically using a hard-sphere model (reproduced...

Large changes in light-scattering dissymmetry indicating the formation of extended micelles were observed for synthetic surfactants in the early 1950s.For such systems it appears that an increase in surfactant concentration always favours the formation of extended micelles rather than globular micelles. 

Fig. 46.—Dissymmetry ratio for light scattered at 45° and 135° as a function of -x/r /X for random coil polymer chains. ...

Turbidity as determined by light-scattering measurements, and the same quantity corrected for dissymmetry (Chap. VII). 

Values of molecular weight (uncorrected for dissymmetry) have been obtained by Harrap and Manners238 from light-scattering investigations, as follows rabbit liver, 6.8 X 106 rabbit muscle, 2.8 X 109 cat liver, 10.0 X 109 fetal sheep liver, 14.8 X 106 Tetrahymena pyriformis, 9.8 X 106 and Ascaris lumbricoides, 8.8 X 106. 

If the intensity of light scattered by a colloidal dispersion is measured as a function of c and 0, the Zimm method enables us to convert this information into several parameters that characterize the colloid M, B, and Rg. In some situations this is more information than is actually needed. If spatial extension is the only information sought, a simpler method for evaluating it employs the so-called dissymmetry ratio. 

Tn the critical region of mixtures of two or more components some physical properties such as light scattering, ultrasonic absorption, heat capacity, and viscosity show anomalous behavior. At the critical concentration of a binary system the sound absorption (13, 26), dissymmetry ratio of scattered light (2, 4-7, II, 12, 23), temperature coefficient of the viscosity (8,14,15,18), and the heat capacity (15) show a maximum at the critical temperature, whereas the diffusion coefficient (27, 28) tends to a minimum. Starting from the fluctuation theory and the basic considerations of Omstein and Zemike (25), Debye (3) made the assumption that near the critical point, the work which is necessary to establish a composition fluctuation depends not only on the average square of the amplitude but also on the average square of the local... 

Figure 6. Cloud-point curve for polystyrene in cyclohexane (%) determined from light scattering and (M) determined visually. The arrows indicate (from left to right) maximum of the cloud-point curve, maximum of the dissymmetry ratiof critical point.

Particles which are too small to show a series of maxima and minima in the angular variation of scattered light are frequently studied by measuring the dissymmetry of scattering (usually defined as the ratio of the light scattered at 45° to that scattered at 135°). The dissymmetry of scattering is a measure of the extent of the particles compared with A. If the molecular or particle size is known, it can be related to the axial ratio of rod-like particles or the coiling of flexible linear macromolecules. 

Compared to the colligative methods light scattering can yield information on a possible dissymmetry of the aggregates. For anisotropic particles the direction of the electric field associated with the incident light may not coincide with the shift of the electron cloud. The intensity of light scattered at (usually) 90° from anisotropic aggregates is increased over the value predicted on the basis of isotropy by the Cabannes factor. 

Figure 12. Changes in apparent particle size with pH of batch MMA-MAA copolymer latexes (determined by dissymmetry method of light scattering)...

Problem 4.19 Using the light-scattering data given in Problem 4.17 for a polystyrene sample with benzene as the solvent determine by the dissymmetry method (a) the molecular weight of the polymer, (b) size of the polymer molecule in solution, and (c) second virial coeflScient for the polymer/solvent system. 

---