Microstructures of Capped Ethylene Oxide Oligomers in Water and N ‐Hexane

Abstract

This report documents microstructural features of CH 3 (CH 2 -O-CH 2 ) m CH 3 dissolved in water and n-hexane for m = 11, 21, and 31. Probability densities for end-toend 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 highextension 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 R g 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.

Statistical Analyses of Hydrophobic Interactions: A Mini-Review

“…Those high-resolution results were matched with direct observation of P ( r ) in the complementary region . Adapted with permission from ref . Copyright 2014 John Wiley and Sons, Inc.…”

“…In contrast with hydrophobic hydration, the association (Figure ) of end-methyl groups capping a poly­(ethylene oxide) (PEO) oligomer in aqueous solution shows a distinct hydrophobic interaction. , That interaction is also suggested by the density profile of poly­(dimethylsiloxane) (PDMS) interacting with a polar surface, even in the absence of aqueous solution . The PEO example was constructed for feasible direct measurement, e.g., by neutron diffraction, of the hydrophobic interactions shown.…”