Optical probe diffusion

For both 0f and pf, there is one behavior at c < c, a crossover at approximately the same concentration for all parameters, and a distinct behavior at c > c. The phenomenology is entirely consistent with a system that has two fundamentally different dynamical behaviors separated by a dynamic crossover at c. There is no indication in the region c < c that one has a series of different behaviors linked by crossovers. Our experimental results based on optical probe diffusion confirm the interpretation of Phillies and Quinlan that r (c) of HPC solutions shows a sharp dynamic transition at a concentration c" 6 g/L. 

This volume presents a systematic analysis of experimental studies on the dynamics of polymers in solution. 1 cover not only classical methods, e.g., rheology, and more modem techniques, e.g., self-diffusion, optical probe diffusion, but also radically innovative methods not generally recognized as giving information on polymer dynamics, e.g., capillary zone electrophoresis. Actual knowledge comes from experiment. The intent is to allow the data to speak for themselves, not to force them into a particular theoretical model in which they do not fit freed of the Procrustean bed of model-driven analysis, the data do speak, loudly and clearly. 

K. A. Streletzky and G. D. J. Phillies. Relaxational mode structure for optical probe diffusion in high molecular weight hydroxypropylcellulose. J. Polym. Sci. B, 36 (1998), 3087-3100. 

As a practical experimental matter, if the particles with bi 0 are dilute (the nonscattering particles having bi = 0 may be nondilute), positions of pairs of scattering particles are not correlated, so and the measured are equal. Equation 4.7 thus describes a dilute suspension of intensely-scattering probe particles diffusing through a nonscattering complex fluid, and therefore forms the basis of optical probe diffusion measurements. 

This section treats four approaches for calculating light scattering spectra of macromolecule solutions. Historically, the methods were primarily applied to colloid particles and protein molecules. Charged colloids are not the center of this volume, but the results clarify the meaning of measurements on polymer solutions. Furthermore, colloid motion is central to studies of optical probe diffusion. Finally, the quantitative success of the colloid calculations indicates that the nature of the forces between diffusing macromolecules in solution is well-understood. 

The literature examined here includes three major experimental approaches, namely (i) optical probe diffusion studies, largely made with quasi elastic light scattering spectroscopy (QELSS), to observe diffusion of dilute probe particles, (ii) particle tracking studies in which the detailed motions of individual particles are recorded, and (iii) true microrheology measurements of the driven motion of mesoscopic probes. 

Historically, particle tracking was first used by Brown to study the motion now called Brownian. Optical probe diffusion based on quasielastic light scattering, as applied to polymer solutions, dates back to Turner and Hallett, who in... 

For clarity, the remaining literature in this section is discussed in chronological order. Work by Phillies and Quinlan had been preceded by extensive optical probe diffusion studies of HPC water solutions Brown and Rymden used QELSS to examine 72 nm radius PSL spheres diffusing in solutions of hydroxyethylcellulose (HEC), hydroxypropylcellulose (HPC), carboxymethylcellulose (CMC), and polyacrylic acid(PAA)(56). The focus was polymer-induced cluster formation, indicated by the substantial decreases in Dp and increases in the second spectral cumulant as seen at very low (0.001 g/g) concentrations of HEC and HPC. These changes were substantially reversed by the addition of 0.15% Triton X-100. The Dp of spheres was reduced by the addition of small amounts of fully-charged pH 9 CMC, but addition of TX-lOO had no effect in CMC solutions. Brown and Rymden also examined sphere diffusion in nondilute polymer solutions. Relatively complex dependences of Dp on concentration were suppressed by the addition of TX-IOO. In the presence of TX-lOO, simple stretched-exponential concentration dependences were observed, but the second spectral cumulant still increased with increasing polymer concentration. 

Ngai and Phillies(61) extend the Ngai-Rendell coupling model(62) to treat probe diffusion and polymer dynamics in polymer solutions. This is not an experimental paper it forces extant experimental data to confront a particular theoretical model, which in the paper was extensively reconstructed to treat the particular experimental methods under consideration. Ngai and Phillies consider zero-shear viscosities and optical probe diffusion spectra for HPC solutions, extracting from them the Ngai-Rendell model relaxation time tq and coupling exponent n. Optical probe spectra and other measurements were used to obtain n in four independent ways, namely from r](c) and from the concentration, time, and wave-vector dependences of g q,t). The four paths from t] and lead to consis-... 

There are already vast numbers of reviews, monographs, edited collections, conference proceedings, and web pages on polymer diffusion, light scattering, electrophoresis, rheology, and almost every topic I cover, other than optical probe diffusion. Why does the world need another book about polymers in solution ... 

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