Scattering from Polymer Systems

LIGHT SCATTERING FROM POLYMER SYSTEMS Laser Potatiser... 

Brillouin scattering measures the velocity and attenuation of hypersonic thermal acoustic phonons. A theory of Brillouin scattering from polymer blends is presented and illustrated qualitatively by several examples. The study of blend compatibility is illustrated for the system PMMA-PVFS. The detection of inhomogeneous additives is shown for commercial PVC film and cellulose acetate, and simultaneous measurements on separated phases are presented for Mylar film. The main purpose of the paper is to stimulate further work in a potentially promising field. 

The scattering from a system of noninteracting spheres and from a system of polymers (long, chainlike molecules) is discussed in the problems at the end of this chapter. 

Derive an expression for the Fourier transform of the density-density correlation function and hence the scattering from a system of dilute, and hence noninteracting polymers. The chains are described by the position R s) of monomer s along the contour. One chain end has s = 0 and the other has 5 = A, for a finite-sized chain of N monomers. The density is related to the position vector by... 

The scattering patterns in Figure 5.2 represent the scatterings from the systems with very low concentrations of rods, as the interference among the rods has been ignored. A liquid crystalline polymer in its bulk state should, however, be treated as a condense matter. A more realistic X-ray scattering pattern from such a system can be obtained only when the interference function is included in the calculation, as shown in Equation (4) in which S(a, (3, T ) is the interference function, or so-called structure factor of the system. 

Quasielashc light scattering was considered in detail in Chapter 4. The discussion here starts where Chapter 4 left off. The optical probe method refers to the special case of measurements on a ternary solvent matrix polymer rigid probe system in which the matrix polymer does not scatter significantly, while the probe species dominates scattering from the system even though it is dilute. Optical probe studies are formally similar to QELSS studies of ternary polymer polymer solvent systems containing an isorefractive polymer solvent pair. 

De Gennes PG (1979) Scaling concepts in polymer physics Cornell University Press, Ithaca Benoit H, Wu W, Benmouna M, Mozer B, Bauer B, Lapp A (1985) Elastic coherent scattering from multicomponent systems applications to homopolymer mixtures and copolymers. Macromolecules 18 986-993... 

Additional neutron scattering studies on different polymer systems could prove very important. Strobl [31,32,47,103] provides evidence that, for some polymers, lamellar crystallization is preceded by pre-ordering of the melt followed by formation of planar arrays of blocks. Investigating crystallization from the melt, Kaji and coworkers [25] find pre-ordering phenomena relating to orientational fluctuations of stiff polymer segments which, under appropriate conditions, determine phase separation prior to crystallization. 

For both polymer systems the static structure factors were investigated using small angle neutron scattering and the results interpreted in terms of RPA theory. Figure 6.6 displays the temperature-dependent static structure factor obtained from a PE-PEE melt (sample IV). 

Random Systems The scattering from random two-phase systems was considered by Debye(13,14) and other accounts are available (15,16) These formulations have been applied to gels of a fairly stiff polymer by Goebel, Berry and Tanner (17,18) If the system is spatially isotropic then ... 

For polymers whose Mw < 10,000, the intensity of light scattering from the solution differs so little from the neat solvent that the determination is not precise. For polymers whose Mw > 10,000, the need to measure the light scattering at very small values of 0 is beyond the capability of many older instruments. Special treatment is required for mixed solvent systems, copolymers, higher polymers, and polyelectrolytes. 

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