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Molecular emulsions: from charge order to domain order
1Laboratoire de Physique Théorique de la Matière Condensée (UMR CNRS 7600), Université Pierre et Marie Curie, 4 Place Jussieu, F75252, Paris cedex 05, France. aup@lptmc.jussieu.fr.
Physical Chemistry Chemical Physics : PCCP
|October 14, 2017
Summary
Micro-segregation in aqueous alcohol mixtures is not detected by scattering pre-peaks due to cancellations. This occurs because species correlations are out-of-phase, masking nano-scale domain structures in scattering data.
Area of Science:
- Physical Chemistry
- Materials Science
- Chemical Physics
Background:
- Aqueous mixtures of small molecules, like n-alkanols, exhibit micro-segregation into nano-meter sized domains.
- This micro-segregation is expected to cause long-range oscillatory correlations and pre-peaks in scattering data, but these are typically absent in experimental results.
Purpose of the Study:
- Investigate the origin of the missing scattering pre-peaks in aqueous n-alkanol mixtures.
- Explain the cancellation mechanism obscuring micro-segregation signals in scattering data.
Main Methods:
- Large-scale molecular simulations of aqueous-1-propanol mixtures.
- Analysis of atom-atom pair correlation functions and structure factors.
- Comparison of X-ray and neutron scattering data.
Main Results:
- The absence of scattering pre-peaks is due to the exact cancellation of contributions from various atom-atom correlations.
- This cancellation arises from out-of-phase, long-range oscillatory correlations (beyond 1 nm) between same and cross species.
- X-ray scattering shows exact cancellation, while neutron scattering cancellation depends on deuteration ratios.
Conclusions:
- Micro-segregation in aqueous n-alkanol mixtures is masked by destructive interference in scattering data.
- The observed cancellation mechanism differs from ionic melts and room temperature ionic liquids.
- Re-evaluation of scattering data analysis is needed to detect micro-segregation in such systems.