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Neutron Spin Echo Spectroscopy (NSE)

Neutron Spin Echo Spectroscopy (NSE). 2003 Summer School NCNR, NIST Gaithersburg, MD 20890. Group A. Alina Visinoiu Erick Lawson Gokhan Caliskan Jose Rodriguez Kapil Gupta Martin Sulic Mike Lewis Tessema Xabiher. Goals: • Spontaneous curvature • Bending elasticity

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Neutron Spin Echo Spectroscopy (NSE)

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  1. Neutron Spin Echo Spectroscopy(NSE) 2003 Summer School NCNR, NIST Gaithersburg, MD 20890 Group A Alina Visinoiu Erick Lawson Gokhan Caliskan Jose Rodriguez Kapil Gupta Martin Sulic Mike Lewis Tessema Xabiher

  2. Goals: • Spontaneous curvature • Bending elasticity • Saddle splay elasticity Spontaneous curvature, bending elasticity, saddle splay elasticity Diffusion shape fluctuations NSE (t scale ~ 1 - 10 ns) Why NSE? H2O Surfactant film C10H22 Surfactant Diffusion: • NMR • Dynamic light scattering (t scale > 100 ns) Shape fluctuations are in very short time and length scales!

  3. Experimental AOT Surfactant molecule Hydrophilic head Hydrophobic tail Experiment I Diffusion of AOT micelles in C10D22 (5.4 % vol. fraction) Experiment II Shape fluctuations in AOT/D2O/C10D22 microemulsion (5.4/4.6/90 % vol. fraction) Inverse microemulsion droplet Inverse spherical micelle Shape fluctuations D2O ~ 25 AOT Translational diffusion AOT C10D22 C10D22 Translational diffusion

  4. • elastic scattering • inelastic scattering   0 ± 0  <cos(±)> Angle B Principle of NSE L Neutrons posses spin and magnetic moment. They precess in magnetic fields with the Larmor frequency that depends on the strangth of the magnetic field only. (g =1.83108 s-1T-1) S N B B sample n !

  5. Experiment II AOT/D2O/C10D22 microemulsion Summary of data analysis Experiment I AOT micelles in C10D22 • Goal: • Calculate the bending modulus of elasticity • Calculate the frequency of deformation

  6. Echo Point determination Echo Point:- Phase current where the magnetic field integral in the two magnets are balanced. • Measured echo point for 13 fourier time points at three Q values (.05,.085,.12)

  7. Results • Faster decay at high Q

  8. Results • Stokes-Einstein Relationship: • D = (1-)kBT/6Rh, • Rmicelle=1.6nm • Remulsion= 3.4nm Values are in good agreement with the SANS Data.

  9. Q independent Q dependent • Fitting model Results

  10. Bending modulus 2- damping frequency <|a|2> - amplitude of deformation p2- size polydispersity, measured by SANS k= .1kBT • Fluctuations are thermal in origin

  11. Summary • Energy resolution is very high (10-5meV) • Measures the Intermediate scattering function(I(Q,t)) • Provides information on the Brownian dynamics of the particle • Very small shape fluctuations can be characterized Acknowledgements • NIST/NCNR staff • NSF

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