Microstructures of capped ethylene oxide oligomers in water and n-hexane

TL;DR

This study investigates the microstructural features of capped ethylene oxide oligomers in water and n-hexane, revealing distinct conformational behaviors and density profiles influenced by solvent type and chain length.

Contribution

It provides detailed microstructural analysis of ethylene oxide oligomers in different solvents, highlighting solvent-specific conformational regions and density distributions.

Findings

Water induces a globule region absent in n-hexane.

Density profiles differ significantly between water and n-hexane.

Internal condensation occurs at the chain centroid in water for smaller chains.

Abstract

This report documents microstructural features of CH3(CH2-O-CH2)mCH3 dissolved in water and n-hexane for m = 11, 21, and 31. Probability densities for end-to-end distance, and the associated potential-of-mean-force (pmf), are more revealing of chain microstructures than are the corresponding results for the radii of gyration. For water, the pmf identifies three distinct regions: loop-closure, globule, and high-extension regions. The globule region affirms a water-swollen chain, and is not evident in the n-hexane results. Chain C-atom density profiles from the chain centroid are also different in the water and n-hexane cases. For n-hexane (but not water), the density profiles are similar for the different chain lengths when the distances are scaled by the observed <Rg^2>^{1/2}. For water (but not n-hexane) and the smaller chains considered, the carbon material exhibits a distinctive enhanced concentration, or internal condensation, at the centroid core of the structure.