Atomistic structure of a micelle in solution determined by wide Q-range neutron diffraction
Rowan Hargreaves1, Daniel T Bowron, Karen Edler
1STFC-ISIS Neutron Scattering Facility, Didcot, United Kingdom. rowan.hargreaves@stfc.ac.uk
Journal of the American Chemical Society
|August 10, 2011
Summary
Neutron diffraction reveals the atomistic structure of surfactant micelles. This study details micelle formation, revealing a hydrophobic core, a disordered corona, and counterion interactions in solution.
Area of Science:
- Physical Chemistry
- Materials Science
- Colloid Science
Background:
- Surfactant micelles self-assemble in solution due to head and tail group affinities.
- Existing models explain micelle size and shape using packing parameters and electrostatics.
Purpose of the Study:
- To determine the complete, atomistic structure of surfactant micelles and their surroundings in solution.
- To provide unprecedented detail on micelle physicochemical properties.
Main Methods:
- Wide Q-range neutron diffraction measurements.
- H/D isotopic substitution of decyltrimethylammonium bromide (C(10)TAB) solutions.
Main Results:
- ~45 surfactant molecules form spherical micelles (radius of gyration 14.2 Å).
- Larger micelles exhibit more ellipsoidal shapes.
- A dry hydrophobic core is surrounded by a corona of headgroups, counterions, water, and alkyl groups.
- A Stern layer contains 0.7 bromide counterions/surfactant molecule, retaining hydration shells.
Conclusions:
- Neutron diffraction provides atomistic resolution of micelle structure.
- Findings align with previous experimental studies on micelle properties.
- Detailed insights into the micelle-solvent interface and counterion behavior are obtained.
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