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Concentration fluctuations and microheterogeneity in aqueous amide mixtures
Larisa Zoranić1, Redha Mazighi, Franjo Sokolić
1Laboratoire de Physique Théorique de la Matière Condensée (UMR CNRS 7600), Université Pierre et Marie Curie, 4 Place Jussieu, F75252 Paris Cedex 05, France.
The Journal of Chemical Physics
|April 2, 2009
Summary
Molecular dynamics simulations reveal microheterogeneity in aqueous amide mixtures, contrasting with experimental data. This study differentiates microheterogeneity from concentration fluctuations using partial site-site structure factors.
Area of Science:
- Physical Chemistry
- Computational Chemistry
- Materials Science
Background:
- Aqueous amide mixtures present complex structural behaviors.
- Experimental data (Kirkwood-Buff integrals) suggest near-ideal mixing.
- Discrepancies exist between simulation predictions and experimental observations.
Purpose of the Study:
- To investigate the microheterogeneous structure of aqueous amide mixtures.
- To reconcile simulation findings with experimental data.
- To analyze the relationship between microheterogeneity and concentration fluctuations.
Main Methods:
- Molecular dynamics simulations of formamide, N-methylformamide, and dimethylformamide mixtures.
- Analysis of partial site-site structure factors.
- Formulation of an analytical statistical model for microheterogeneity.
Main Results:
- Simulations show significant microheterogeneity in aqueous amide mixtures.
- Microheterogeneity arises from H-bonding constraints, distinct from concentration fluctuations.
- Partial site-site structure factors reveal distinct signatures for microheterogeneity (small wave-number prepeaks) and concentration fluctuations (zero wave-number value).
Conclusions:
- Microheterogeneity and concentration fluctuations are distinct phenomena in aqueous amide mixtures.
- The study provides a framework for understanding transient cluster formation kinetics.
- The findings offer insights into the molecular-level structure of amide-water systems.
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