Association and microheterogeneity in aqueous 2-butoxyethanol solutions

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Understanding the behavior of 2-butoxyethanol (BE) in aqueous solutions is crucial for various chemical applications.
• Previous experimental studies suggest aggregation phenomena in BE-water mixtures, but the precise mechanisms and structures remain elusive.
• Microheterogeneity and self-assembly in dilute solutions are complex phenomena requiring advanced simulation techniques for detailed investigation.

Purpose of the Study:

• To investigate the aggregation behavior and microheterogeneity of 2-butoxyethanol (BE) in dilute aqueous solutions using molecular dynamics simulations.
• To determine the critical concentration for BE aggregation and characterize the structure and size of the formed aggregates.
• To compare simulation results with existing experimental data for validation and further insight.

Main Methods:

• Employed large-scale molecular dynamics simulations with systems comprising up to 32,000 molecules to capture aggregate formation.
• Utilized two distinct force fields to ensure the robustness and reliability of the simulation outcomes.
• Analyzed pair correlation functions and density oscillations to identify microheterogeneity and estimate aggregate dimensions.

Main Results:

• Observed intramolecular hydrogen bonds in 2-butoxyethanol (BE) at very low concentrations, forming five-member ring structures.
• Detected initial signs of BE association around a mole fraction of 0.005, with rapid aggregation leading to micelle-like structures by 0.02.
• Estimated aggregate radius at X(BE) = 0.04 to be approximately 42 Å, consistent with experimental light scattering and neutron scattering data.

Conclusions:

• Molecular dynamics simulations confirm the formation of micelle-like aggregates of 2-butoxyethanol (BE) in water at concentrations above X(BE) ≈ 0.005.
• The simulation results align well with experimental observations, validating the model's ability to reproduce aggregation phenomena.
• The study provides quantitative insights into the length scales of microheterogeneity and the structural evolution of BE aggregates in aqueous solutions.