Translational diffusion of small and large mesoscopic probes in hydroxypropylcellulose-water in the solutionlike regime

Abstract

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.

Relaxational mode structure for optical probe diffusion in high molecular weight hydroxypropylcellulose

“…22 The following sections introduce experimental methods, give the important results of ref. 20, present a coupling/scaling model analysis of our data, and discuss the modes' physical interpretations.…”

“…This article addresses the results of a study 20 of probe diffusion in aqueous solutions of hydroxypropylcellulose. The scattering from probes diffusing in this polymer solution reveals a bimodal S(q, t).…”

“…An apparent influence of the probe size on the relaxational mode structure was discovered. 20 The detailed lineshape analysis can be found in ref. 20.…”

“…20 The detailed lineshape analysis can be found in ref. 20. Here we discuss properties of the spectral parameters that reveal the physical nature of the relaxational mode structure.…”

“…The scattering from probes diffusing in this polymer solution reveals a bimodal S(q, t). Lineshape analysis of S(q, t) was employed 20 for this system, finding two distinct modes of the relaxation. An apparent influence of the probe size on the relaxational mode structure was discovered.…”