Probe Diffusion in Hydroxypropylcellulose−Water: Radius and Line-Shape Effects in the Solutionlike Regime

Abstract

Light-scattering spectroscopy was used to examine diffusion of optical probes of various radii in solutions (0 ≤ c ≤ 15 g/L) of 300 kDa hydroxypropylcellulose (HPC) at 25 °C. Spectra follow well a stretched-exponential g(1)(t) = A exp(−θtβ) ≡ A exp((t/τ)β), plus at elevated c a weak, rapid initial decay. Accurate values for θ, β, and τ were obtained via multi-τ spectral splicing techniques. For 109, 189, and 760 nm diameter spheres, θη (η is the solution viscosity) is independent of c. HPC:water shows pseudo-Stokes−Einsteinian behavior for large probes. For 21 nm probes, θη increases by 10-fold over 0 ≤ c ≤ 15 g/L. From the η and scattering vector dependences, θ and β are inferred to be the quantities most likely to be amenable to direct theoretical calculation.