Experimental Compressibilities and Structure Factors of Poly(ethylene glycol)Molecular Masses 2000 to 8000 in Aqueous-Solution

Published

June 5, 2009

Author(s)

Kenneth A. Rubinson

Abstract

Small-Angle Neutron Scattering (SANS) is a powerful nondestructive technique that can measure simultaneously macroscopic compressibilities of solutions, overall shapes of macromolecular solutes, as well as their intermolecular structural correlations. We have conducted SANS experiments on aqueous solutions of polyethylene glycols (PEGs) with nominal molecular masses 2000, 4000, and 8000 Da over the q-range 0.03-0.30 Å ^-1 [q = (2π/λ) sin θ]. By incorporating accurate background subtraction, our extrapolations of the intermolecular structure factor S(q) down to S(0) indicate a significant and systematic dependence of the solutions' compressibility on both molecular mass and concentration of PEG, unlike the solutions' osmotic pressures. This implies that the structure of water in the vicinity of PEG is considerably altered relative to the bulk state even though the activity coefficient of water remains nearly invariant in the range. Graphs of S(q) for 3% w/w to 17% w/w solutions each show a gradual rise from the low-q side to a broad plateau, which indicates weak intermediate-range correlations between oligomers that are probably associated with soft, repulsive, solvent-mediated PEG-PEG interactions. Since both the water and PEG change structures from their neat forms, any quantitative assignment of changes in partial volumes must necessarily be arbitrary.

Citation

The International Journal for the Science and Technology of Polymers

Volume

50

Issue

12

Pub Type

Journals

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Keywords

SANS, PEG, structure factor, osmotic compressibility, poly(ethylene glycol)

Citation

Rubinson, K. (2009), Experimental Compressibilities and Structure Factors of Poly(ethylene glycol)Molecular Masses 2000 to 8000 in Aqueous-Solution, The International Journal for the Science and Technology of Polymers, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=33047 (Accessed April 19, 2024)