Mutual Diffusivities of Binary Mixtures of Water and Poly(ethylene) Glycol from Heterodyne Dynamic Light Scattering

Abstract

In the present study, the mutual diffusivity D11 in binary mixtures of water with technical polydisperse poly(ethylene) glycol (PEG) blends with molar masses of (1000, 4000, or 6000) g⋅mol−1 as well as with a purified monodisperse PEG homolog with a polymerization number of 21 and a molar mass of 943 g⋅mol−1 was investigated by heterodyne dynamic light scattering (DLS) as a function of temperature and/or PEG concentration. The measured D11 for technical PEG 1000 and pure PEG 943 match within the experimental uncertainties and agree well with the available literature data. D11 decreases with increasing molar mass of the PEGs at constant temperature and weight fraction. For the technical PEG 4000, it could be shown that D11 increases with increasing temperature and exhibits a non-linear concentration dependence. This study demonstrates that heterodyne DLS can be applied for the reliable determination of D11 of aqueous solutions of PEGs over a broad range of PEG weight fractions from 0.01 up to the solubility limit with an average expanded uncertainty (k = 2) of 5.5%. Moreover, the results show that monodisperse PEGs are suitable model systems for studying the diffusion behavior of bimodal and also multimodal particulate systems.

Separation of Molar Weight-Distributed Polyethylene Glycols by Reversed-Phase Chromatography – Analysis and Modelling Based on Isocratic Analytical-Scale Investigations

“…Chromatographic separation of molar weight-distributed PEGs may be a flexible and interesting alternative, since it could provide monodisperse PEGs with intermediate MWs. For example, simple scale-up of the methods described in this work yielded a pure single homolog of PEG 1000, which was then used for determining diffusion coefficients by heterodyne dynamic light scattering [9]. Another feature of chromatography is that it can deliver simultaneously a large number of individual homologs within a homologous series, thus including the homologs and their "direct neighbors" within a molar weight distribution (MWD).…”