On the Behavior of the Ethylene Glycol Components of Polydisperse Polyethylene Glycol PEG200

Abstract

Molecular dynamics (MD) simulations are reported for [polyethylene glycol (PEG)200], a polydisperse mixture of ethylene glycol oligomers with an average molar weight of 200 g·mol–1. As a first step, available force fields for describing ethylene glycol oligomers were tested on how accurately they reproduced experimental properties. They were found to all fall short on either reproducing density, a static property, or the self-diffusion coefficient, a dynamic property. Discrepancies with the experimental data increased with the increasing size of the tested ethylene glycol oligomer. From the available force fields, the optimized potential for liquid simulation (OPLS) force field was used to further investigate which adjustments to the force field would improve the agreement of simulated physical properties with experimental ones. Two parameters were identified and adjusted, the (HO)–C–C–O proper dihedral potential and the polarity of the hydroxy group. The parameter adjustments depended on the size of the ethylene glycol oligomer. Next, PEG200 was simulated with the OPLS force field with and without modifications to inspect their effects on the simulation results. The modifications to the OPLS force field significantly decreased hydrogen bonding overall and increased the propensity of intramolecular hydrogen bond formation at the cost of intermolecular hydrogen bond formation. Moreover, some of the tri- and more so tetraethylene glycol formed intramolecular hydrogen bonds between the hydroxy end groups while still maintaining strong intramolecular interactions with the ether oxygen atoms. These observations allowed the interpretation of the obtained RDFs as well as structural properties such as the average end-to-end distances and the average radii of gyration. The MD simulations with and without the modifications showed no evidence of preferential association of like-oligomers to form clusters nor any evidence of long-range ordering such as a side-by-side stacking of ethylene glycol oligomers. Instead, the simulation results support the picture of PEG200 being a random mixture of its ethylene glycol oligomer components. Finally, additional MD simulations of a binary mixture of tri-and hexaethylene glycol with the same average molar weight as PEG200 revealed very similar structural and physical properties as for PEG200.

Direct and Indirect DNP NMR Uncovers the Interplay of Surfactants with Their Mesoporous Host Material

“…As for the MCM 41 porous material, especially the larger surfactants investigated in this work, C 10 E 6 and Triton with an average of six and nine ethylene glycol units, respectively, are approximately as long or longer than the pore diameter. However, as the investigated surfactants are not rigid molecules, they are expected to coil via the formation of inter- and intramolecular hydrogen bonds for the PEG units and van der Waals interactions for the hydrocarbons, as well as by entropic forces. − This behavior reduces the effective length of the surfactants to a fraction of their length in the stretched conformation, , therefore allowing for the absorption into the pores.…”

“…Additionally, all carbons are neighboring oxygen atoms that are able to accept hydrogen bonds. Statistically, any carbon can point toward the silica surface and the terminal hydroxyl group could also point inward into the coiled PEG to form hydrogen bonds . The molecules C 10 E 6 and Triton consist of a hydrophilic moiety (the PEG unit) and a hydrophobic moiety (the aliphatic carbon chain and the tetramethylbutylphenyl group, respectively) and are amphiphilic.…”

“…Statistically, any carbon can point toward the silica surface and the terminal hydroxyl group could also point inward into the coiled PEG to form hydrogen bonds. 65 The molecules C 10 E 6 and Triton consist of a hydrophilic moiety (the PEG unit) and a hydrophobic moiety (the aliphatic carbon chain and the tetramethylbutylphenyl group, respectively) and are amphiphilic. The hydrophobic groups cannot interact with the surface of the silica pores and cannot form hydrogen bonds.…”

Fortified Lubricating Response to Sustainable PEG System from Protic Ionic Liquid and Their Strong Hydrogen Bonding Network

“…31 In addition, the exploration of interface behavior, 32−34 IL heterogeneous microstructures, 35,36 and solvent effect 37,38 can enrich and deepen the interaction mechanisms of the IL lubricating system. That is, more than just the interaction between the base system and the substrate, the optimal balance between the base system and the functional additives needs to be considered, which is manifested in the molecular behavior 39 and component formulation. 40,41 The pure polyethylene glycol system may be unstable in severe operating conditions, and the abundant polar oxygen in its ether chain and the terminal hydroxyl groups can be adsorbed to the metal surface, but this is weak physisorption.…”

“…In addition, the exploration of interface behavior, − IL heterogeneous microstructures, , and solvent effect , can enrich and deepen the interaction mechanisms of the IL lubricating system. That is, more than just the interaction between the base system and the substrate, the optimal balance between the base system and the functional additives needs to be considered, which is manifested in the molecular behavior and component formulation. , …”