TRANSLATIONAL DIFFUSION OF SMALL AND LARGE MESOSCOPIC PROBES IN HYDROXYPROPYLCELLULOSE-WATER IN THE SOLUTIONLIKE REGIME

Quasi-elastic light scattering spectroscopy was used to study the tran slational diffusion of monodisperse spheres in aqueous 1 MDa hydroxypr opylcellulose (HPC) at 25 degrees C. Probe diameters d spanned 14-455 nm; HPC concentrations were 0 less than or equal to c less than or equ al to 7 g/L. Light scattering spectroscopy consistently found spectra having the form g((1))(t) = (1 - A(f))exp(- theta t(beta)) + A(f) exp( - theta(f)t(beta)f). Here theta(f) and Pf refer to the ''fast'' mode; theta and beta describe the ''slow'' mode. We examine the dependence o f theta, beta, theta(f), beta(f), and A(f) on d, c, scattering vector q, and viscosity eta. beta = 1 for large probes; elsewise, p and ef ar e E (0,1). The slow mode, with short-lived memory function, is diffusi ve; for large probes theta approximate to(d eta)(-1). The fast mode, w ith long-lived memory function, appears coupled to polymer chain inter nal dynamics. Probe behavior differs between ''small'' and ''large'' p robes. Small probes have diameters d<R-h, R-h being the chain hydrodyn amic radius. Large probes have d greater than or equal to R-g, R-g bei ng the polymer radius of gyration. (C) 1998 American Institute of Phys ics.