Polymer solution dynamics may be inferred from light scattering spectra of dissolved optical probe particles. We compare a variety of probes in solutions of several polymers. In the "overlapping" concentration/molecular weight regime, the Stokes-Einstein equation fails by up to a factor of 2, while the probe diffusion coefficient D follows a scaling law D / Do = exp( -aM" C V Rfj) (c, M, and R are the polymer concentration, molecular weight, and the probe radius, respectively). Experimentally, r = 0.8 ± 0.1, v = 0.6-1.0, and /) = -0.1 to 0, contrary to the theoretical predictions r = 0 and /) = 1. With very high molecular-weight polymers, we observe a further "entangled" regime, characterized by huge (10 4 ) failures of the Stokes-Einstein equation and the appearance of "fast" modes in the scattering spectrum.
A new quantitative X-ray powder diffraction (QXRPD) method has been developed to analyze polyphase crystalline mixtures. The unique approach employed in this method is the utilization of the full diffraction pattern of a mixture and its reconstruction as a weighted sum of diffraction patterns of the component phases. To facilitate the use of the new method, menu-driven interactive computer programs with graphics have been developed for the VAX* series of computers. The analyst builds a reference database of component diffraction patterns, corrects the patterns for background effects, and determines the appropriate reference intensity ratios. This database is used to calculate the weight fraction of each phase in a mixture by fitting its diffraction pattern with a least-squares best-fit weighted sum of selected database reference patterns.The new QXRPD method was evaluated using oxides found in ceramics, corrosion products, and other materials encountered in the laboratory. Experimental procedures have been developed for sample preparation and data collection for reference samples and unknowns. Prepared mixtures have been used to demonstrate the very good results that can be obtained with this method.
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