Study of the end-to-end probability distributions of low-molecular weight, aqueous polyethylene oxide solutions using experimental DEER measurements and molecular dynamics simulations*

Low molecular weight, dilute, aqueous polyethylene oxide (PEO) chain end-to-end distance (R_ee) probability distributions, P(r), were measured experimentally and calculated from simulation, filling a fundamental gap in the existing literature for one of the most widely used water soluble polymers. The distributions were measured by Double Electron Electron Resonance (DEER) spectroscopy, resolving the full P(r) distribution within the technique’s range of validity (~2-9 nm). The DEER technique uses small spin probes conjugated to the polymer ends. The probes in simulation are observed to hydrophobically aggregate below the range accessible to DEER (<1.5 nm), with the perturbation to the distributions dropping off rapidly with molecular weight. The distributions and their average R_ee indicate aqueous PEO is a semi-flexible polymer in good solvent. The average R_ee exhibits excluded volume scaling with molecular weight above the Kuhn length (~0.96 nm), which is quantitatively consistent with scattering data from high molecular weight (>10kDa) PEO.