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Published on: August 15, 2016
Different submicellar solubilization mechanisms revealed by 1H NMR and 2D diffusion ordered spectroscopy (DOSY)
Mengjian Wu1, Zhaoxia Wu, Shangwu Ding
1Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen, China. cuixh@xmu.edu.cn.
This study reveals distinct submicellar solubilization mechanisms for Triton X-100 (TX-100)/tetradecane and sodium dodecyl sulfate (SDS)/butyl methacrylate systems. Differences below the critical micelle concentration (CMC) are driven by solute-surfactant properties, impacting molar solubilization ratios (MSRs).
Area of Science:
- Colloid and Surface Chemistry
- Supramolecular Chemistry
- Physical Chemistry
Background:
- Understanding how non-ionic and ionic surfactants solubilize hydrophobic molecules is crucial for various applications.
- Submicellar solubilization mechanisms, occurring below the critical micelle concentration (CMC), are less understood than micellar solubilization.
- Investigating these mechanisms provides insights into molecular interactions and self-assembly processes.
Purpose of the Study:
- To elucidate the distinct molecular-scale solubilization mechanisms of Triton X-100 (TX-100)/tetradecane and sodium dodecyl sulfate (SDS)/butyl methacrylate systems below and above their CMCs.
- To compare the influence of different surfactant types (non-ionic vs. ionic) and solutes on solubilization behavior.
- To determine the role of intermolecular interactions in submicellar solubilization.
Main Methods:
- Utilizing 1H Nuclear Magnetic Resonance (NMR) spectroscopy to observe molecular changes.
- Employing 2D Diffusion Ordered Spectroscopy (DOSY) to analyze molecular diffusion and aggregation.
- Quantifying solubilization through Molar Solubilization Ratios (MSRs) at varying surfactant concentrations.
Main Results:
- Both tetradecane and butyl methacrylate exhibit enhanced solubility even below their respective CMCs, contributing to early micelle formation.
- The TX-100/tetradecane system shows solubilization driven by hydrophobic interactions (molecular-pair formation) below the CMC.
- The SDS/butyl methacrylate system demonstrates solubilization influenced by polar interactions between butyl methacrylate and SDS head groups below the CMC, with aggregation occurring above the CMC.
Conclusions:
- Above the CMCs, both systems exhibit similar micellar solubilization behaviors.
- Below the CMCs, distinct submicellar solubilization mechanisms are observed, primarily due to differences in solute and surfactant properties.
- These variations in mechanisms lead to different MSRs and specific solubilization sites within the aggregates.
