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Temperature-dependent hydration at micellar surface: activation energy barrier crossing model revisited
Rajib Kumar Mitra1, Sudarson Sekhar Sinha, Samir Kumar Pal
1Unit for Nanoscience and Technology, Department of Chemical, Biological, and Macromolecular Sciences, S. N. Bose National Center for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700098, India.
The Journal of Physical Chemistry. B
|June 15, 2007
Summary
The activation energy barrier crossing model for micellar surface solvation is validated across a wide temperature range. Solvation times decrease with increasing temperature, supporting the model by analyzing water molecule conversion dynamics.
Area of Science:
- Physical Chemistry
- Supramolecular Chemistry
- Chemical Physics
Background:
- Controversy exists regarding the validity of the activation energy barrier crossing model at micellar surfaces.
- Previous studies lacked a wide temperature range and strict control over probe solubility and micelle structure.
- Understanding solvation dynamics is crucial for micellar chemistry and interfacial phenomena.
Purpose of the Study:
- To investigate the solvation dynamics of 4-(dicyanomethylene)-2-methyl-6(p-dimethylamino-styryl) 4H-pyran (DCM) in sodium dodecyl sulfate (SDS) micelles.
- To rigorously test the activation energy barrier crossing model by employing a wide temperature range (298-348 K).
- To ensure probe insolubility in bulk water and minimize micelle structural perturbations during the study.
Main Methods:
- Time-resolved solvation dynamics using a probe fluorophore (DCM).
- Dynamic Light Scattering (DLS) to measure micelle size changes with temperature.
- Sound velocity measurements to determine micelle hydration numbers.
- Time-resolved fluorescence anisotropy to confirm probe localization within the micellar interface.
Main Results:
- DCM remained insoluble in bulk water across the studied temperature range.
- SDS micelle size showed insignificant changes, while hydration numbers decreased with increasing temperature.
- The probe (DCM) consistently remained within the micellar interface.
- Average solvation time decreased as temperature increased.
Conclusions:
- The study validates the activation energy barrier crossing model for micellar surface solvation.
- Solvation occurs via the conversion of interfacially bound water molecules to free water molecules.
- The calculated activation energy (Ea) of 3.5 kcal mol-1 aligns with molecular dynamics simulations.
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