Computational Study on Molecular Aggregation Behavior in Aqueous Mixtures using Molecular Dynamics Simulation and Graph Theoretical Analysis
- Abstract
- Alcohol aqueous mixtures have received considerable attention due to the various properties resulting from the intermolecular interactions of the water-water, alcohol-alcohol, and water-alcohol. Among many properties, molecular aggregation behavior comparably gained a much higher research interest, and in this regard, several exhaustive studies have been conducted accordingly. Nevertheless, the reason for the different aggregation behavior of dissolved molecules and the effect on the water H-bond network is still poorly understood and lacks a quantitative explanation. There are two morphologically distinct aggregation behaviors classified into water-compatible and water-incompatible networks, and these behaviors have been previously established in salt solutions. Herein, these two distinct network types are applied in alcohol-water mixtures to investigate the reasons for the different aggregation behavior of dissolved alcohol molecules and their effect on the water H-bond network by combining molecular dynamics simulation and graph theoretical analysis.
Interestingly, methanol, ethanol, and n-butanol show similar aggregation behavior in pure liquid despite different chain lengths. But, methanol and ethanol exhibit a water-compatible network, where the alcohol H-bond network and water H-bond network are well intertwined. However, the H-bond network of n-butanol aggregates exhibits a different behavior, a water-incompatible network, and tends to segregate from the water H-bond network. Despite the fact that n-butanol, sec-butanol, isobutanol, and tert-butanol have various aggregate sizes and molecular shapes, there are no obvious differences in the network properties of pure alcohol aggregates depending on the type of butanol isomer. However, the n-butanol, sec-butanol, and isobutanol form a chain-like H-bond network in both pure alcohols and alcohol-water mixtures, while the tert-butanol forms small H-bond aggregates because of its distinctive globular-like molecular shape. Dispersion forces between the chain-like aggregates encourage the formation of bigger alcohol aggregates by pressing water molecules away from them. In contrast, tert-butanol forms small-sized aggregates due to its globular-like molecular shape and does not form large butanol aggregates because of the poor dispersion interactions between the aggregates. n-Butanol-water mixture exhibits upper critical solution temperature behavior. At a specific mole fraction, heating changes the alcohol aggregation pattern from two split liquid phases to one single phase. This research is expected to help understand fundamental issues of aggregation behavior, such as miscibility and phase separation in binary aqueous mixtures.
- Author(s)
- Seungeui Choi
- Issued Date
- 2023
- Type
- Thesis
- URI
- https://scholar.gist.ac.kr/handle/local/19026
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