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Quasi-elastic light scattering spectroscopy was used to study the translational diffusion of monodisperse spheres in aqueous 1 MDa hydroxypropylcellulose ͑HPC͒ at 25°C. Probe diameters d spanned 14-455 nm; HPC concentrations were 0рcр7g/L. Light scattering spectroscopy consistently found spectra having the form g (1) (t)ϭ(1ϪA f)exp(Ϫ t ␤)ϩA f exp(Ϫ f t ␤ f). Here f and ␤ f refer to the ''fast'' mode; and ␤ describe the ''slow'' mode. We examine the dependence of , ␤, f , ␤ f , and A f on d, c, scattering vector q, and viscosity. ␤ϭ1 for large probes; elsewise, ␤ and ␤ f are (0,1). The slow mode, with short-lived memory function, is diffusive; for large probes Ϸ(d) Ϫ1. The fast mode, with long-lived memory function, appears coupled to polymer chain internal dynamics. Probe behavior differs between ''small'' and ''large'' probes. Small probes have diameters dϽR h , R h being the chain hydrodynamic radius. Large probes have dуR g , R g being the polymer radius of gyration.

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The structure and dynamics of crosslinked nanoparticles (microgels) made out of hydroxypropylcellulose (HPC) polymer chains were studied using dynamic light scattering spectroscopy. The microgel light scattering spectra were found to be highly nonexponential requiring a spectral time moment analysis in which the spectra were fit to a sum of stretched exponentials. Each term offers three parameters for analysis and represents a single spectral mode. At room temperature microgel spectra reveal three modes. Two faster modes are almost diffusive and correspond to apparent sizes of 25 and 450–650 nm. The slowest mode is independent of scattering angle and is reminiscent of the slow polymer mode observed in identical non‐crosslinked polymer solutions. When solution temperature is varied from 23 to 45°C and back, the microgel undergoes a reversible volume phase transition between 40 and 45°C. According to the time‐moment analysis, above the transition temperature two faster modes collapse into one with apparent hydrodynamic radius of 100–150 nm, while the slow mode remains largely unchanged. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 771–781, 2008

A systematic analysis of the mode structure of diffusive relaxations in 1 MDa hydroxypropylcellulose͑HPC͒:water is presented. New methods and data include ͑1͒ use of integral spectral moments to characterize nonexponential decays, ͑2͒ spectra of small probes in concentrated HPC solutions, ͑3͒ temperature dependence of the mode structure, and ͑4͒ comparison of optical probe spectra and spectra of probe-free polymer solutions. We find that ͑1͒ probe and polymer relaxations are in general not the same; ͑2͒ the apparent viscometric crossover near c t Ϸ6 g/l is echoed by probe behavior; ͑3͒ our HPC solutions have a characteristic dynamic length, namely the 50 nm length that matches the polymer's hydrodynamic radius; ͑4͒ characterization of spectral modes with their mean relaxation time affords simplifications relative to other characterizations; and ͑5͒ contrary to some expectations, Stokes-Einsteinian behavior ͑diffusion rate determined by the macroscopic viscosity͒ is not observed, even for large probes in relatively concentrated solutions. We propose that the viscometric and light scattering effects found in HPC solutions at elevated concentrations reflect the incipient formation of a generalized Kivelson ͓S. A.