Microemulsion Dynamics fromNeutron Spin Echo

Spectroscopy

Group DNCNR Summer School

2007

Sheila Khodadadi, Maggie Johnson, Jacob Tarver

Why study microemulsions?

1987 J. Huang et alPRL 59

Role of interfacetension vs bendingenergy

Fluctuations drivenby bending elasticity

2nm

How do we measure the dynamics?

0.05-15ns

SANS Structure Factor

Radius ~30A

Coherent scattering-collectivedynamics of surfactant shell

Contrast Match SLDs

solvents(D20, d-hexane)~6.1E-6

Surfactant (AOT) ~0.7E-6

NSE Spectrometer

Scatters from the nuclear interactionMeasured property-Final polarization

!

"# $%tF

!

tF"#3I

I is field Integral

Elastic Scatter

Data - Intensity for 1 detector

!

PZ =2A

Nup " Ndown

A

Also normalize to Carbon powder (Resolution)

Results on microemulsion

I(Q,t) atQ=.065,0.1,0.125

13 fourier times atλ=6A

!

I(Q,t)

I(Q,0)= exp "Deff (Q)Q

2t( )

Results-Elastic modulus

Q

Def

f

!

Deff (Q) = Dtr (Q) + Ddef (Q)

Extract Fit parameters R0, a2, Dtr,λ2

k=0.25kT

Conclusions

Were able to measure dynamics andelastic modulus for surfactant shell

Subsequent experiments have used spin-echo to study elastic modulus ofmembranes. (Bossev 2005 SS Invited Talk)

Acknowledgments

Antonio Faraone, Yamali HernandezMichihiro Nagao , Jason Gardner, Maikel

RheinstadterSummer School Instructors & PresentersJulie KeyserDAVE software http://www.ncnr.nist.gov/dave/download.hmtl

CHRNSTHANKS!