1

Bending Modulus of MicroemulsionsUsing Neutron Spin Echo Spectrometer

Group AMohan babu Boggara

Xihua ZhaoZheng Yi

Joel HeltonElvis ZambranoLillian FrazierNina VerdalJiaqiang Yan

Outline

• Colloidal systems (Microemulsions)

• Neutron Spin Echo Spectrometer

• Data Analysis

• Results and Discussion

2

H2O

C6H14Surfactant

Colloidal systems

H2O

SurfactantCylindrical micelles Lamellae

H2O

Vesicles

Properties of the surfactant film:

• Interfacial tension• Lateral elasticity• Spontaneous curvature• Bending elasticity• Saddle splay elasticity

D2O(deuterated)

C6D14(deuterated)AOT

(hydrogenated)AOT/D2O/d-Hexane –5.1/2.5/92.4 v/v% φ= 0.077= 7.7%

Neutron Spin Echo• δδδδE=10-5–10-2 meV (very small!!!) -- Fourier time of 10 ps to 100 ns• Q = 0.05- 1.25 Å-1 (Resolution : +/- 0.02 Å-1)

• Cold neutrons: λ = 5 – 12 Å, E = 0.5 – 3.3 meV

�

S

B B

�/2 flipper �/2 flipper� flipper

3

NSE-Data Reduction and Analysis

Carbopack—Fully Elastic scattering (For Resolution Measurement)Background—SolventSample– Quasi-elastic ScatteringMicro emulsion information– Average size and polydispersity from SANS

4

Intermediate Scattering function

(Isample-Ibackground)/IResolution

Fourier time

Q

( )( ) ( )[ ]tQQD

tQItQI 2exp

0,, −==

Diffusion Coeff. of Droplet Deformation

( )

( )[ ] ( )���

��� +

+=2

2022

002

22022

54

5)(

aQRfQRjQ

aQRfDQD treff

π

λ

5

Bending Modulus of Elasticity

���

�

���

� ++=η

ηηηλπ 3

32'23481 3

022R

p

Tkk B

λ2 –frequency of deformation<|a|2> –amplitude of deformationp2 – size polydispersity, measurable by SANS or DLS

Farago et al. (1990)

Our Result: k /kBT = 0.24 @ 298K

Acknowledgments

Dobrin P. Bossev, Antonio Faraone, Steve Kline and Larry Kneller for their dedication and support during the experiments.

The entire NCNR staff for organizing the 2005 summer school.

6

Questions

Echo-point

0

2000

4000

6000

8000

1 104

1.2 104

-4 -2 0 2 4

1nsec_8A_19990609.dat1 cm apertures before solmain1 and after solmain2

solphase1 = 1.1296 A

Cou

nts/

35se

c

Phase Current (solphase2) (A)

y = m1*exp(-(m0-m2)*(m0-m2)/...13.7085159m1

9.1772e-050.56644m2 0.00429611.238m3 3.552e-050.23287m4

2.66367229.4m5 NA2539.1Chisq