PHASE BEHAVIOR AND 

STRUCTURE OF 

MICROEMULSIONS

Shuzhen Chen

Katie Weigandt and Javen Weston

NIST Center for Neutron Research
What are Surfactants?

Ramanathan

et al. Phys. 

Chem. Chem. 

Phys. 2013

Surfactant

Water

or

Oil

SelfAssembled 

Structure
What are Microemulsions?

Serra et al. Elsevier 2014

oil

Water
Applications

Lawrence et al. Elsevier 2012

Malik et al. Arabic Journal of 

Chemistry 2012
Objective & Motivation

■ Previously, an interesting gel was found 

with Isopar L

– Impure solvent

– Mixture of various alkanes 

■ To reproduce the gel but with pure alkane 

and a similar anionic surfactant system

■ To investigate the shear-induced gelation 

phenomenon
Sample 

Preparation  Surfactant: Alforterra® K2

-

41S

 Sodium Chloride (NaCl)  Oils: hexane, heptane, 

octane, decane, and 

dodecane

+NaCl
Phase Behavior

14 19 24 29 34

NaCl Concentration

Winsor I Winsor II Winsor III

Decane

Dodecane

Heptane

Hexane

Octane

I III II
Small Angle Neutron Scattering (SANS)

Various Alkanes

Water

Oil

Surfactant
SANS of Two Phases

SAMPLE STUDIED HERE:

Type III with no excess 

oil phase
Middle Phase of 

Various Alkane at 

the Optimal Salinity

0.1

1

10

100

1000

10000

0.001 0.01 0.1 1

Intensity (cm-1)

q (A-1)

Dodecane

Decane

Octane

Heptane

Hexane
Teubner-Strey Model Fitting

Mihailescu et al. Journal of Chemical Physics 2001

d

ξ 0.1

1

10

100

1000

10000

0.001 0.01 0.1 1

Intensity (cm-1)

q (A-1)
Domain Size for the Middle Phase of Various 

Alkanes

0

200

400

600

800

1000

5 7 9 11 13

d (Å)

Alkane Length

Domain Size of Alkanes
Objective

■ To reproduce the gel 

but with pure alkane 

and a similar anionic 

surfactant system

■ To investigate the 

shear-induced 

gelation 

phenomenon
Shear-Induced Gelation

Vortexed

0 0.05 0.1 0.15 0.2 0.25

Oil:Water Ratio

Decane Dodecane Heptane

No Gel Gel

14 19 24 29

NaCl Concentration

Decane

Dodecane

Heptane

Hexane

Octane

Optimal salt concentration
Small Angle Neutron Scattering (SANS)

Oil to Water Ratio Scan

Water

Oil

Surfactant
Oil scan at 22% 

NaCl in Decane 

and D2O and H2O

0.1

1

10

100

1000

10000

0.001 0.01 0.1 1

Intensity (cm-1)

q (A-1)
Domain Size for the Oil Scan

0

100

200

300

400

500

600

0 0.05 0.1 0.15 0.2 0.25 0.3

d (Å)

Oil:Water Ratio

Domain Size of Decane Scan
Rheology

 The study of flow and 

deformation of materials

 Investigate the 

viscoelastic properties of 

the shear-induced gel

 Time scale of thixotropy 

(change of viscosity due 

to stress)

 Mechanical property—

strength of gel
Flow Curve

Critical Shear rate

 Below —phase separation

 Above —stable system and shear 

thickening

Gel decays over time 
0.1

1

10

100

1 10 100

G′ and G′′ (Pa)

Angular Frequency (rad/s)

G'

G''

Frequency Sweep for Dodecane Emulsion 

 G′ - Storage modulus or storage 

of elastic energy 

 G′′- Loss modulus or dissipation 

of elastic energy
Strength of Various Alkane Gels

0.01

0.1

1

10

100

0 0.05 0.1 0.15 0.2 0.25 0.3

G’ (Pa)

Oil:Water Ratio

Dodecane

Decane

Heptane
RheoSANS Preliminary Results

RheoSANS

L. Porcar (NIST), J. Moyer (NIST), P. D. Butler (NIST), L. D. Pozzo (NIST, UW)

G. Langenbucher (Anton Paar)

Scattering of 5% Decane at 350 s-1
Conclusions

■ Increase in alkane length increases the optimal salt 

concentration and decreases the domain size 

■ Alkane length does not affect the conditions where shear-induced 

gels form

■ Heptane gel is weaker compared to that of decane and dodecane

Future Works

■ RheoSANS –Below and above oil:water gel 

ratio 

■ RheoSANS with different contrast points

Water

Oil

Surfactant

Water

Oil

Surfactant
Acknowledgement

 Katie Weigandt and Javen Weston

 NIST and NCNR

 Center for High Resolution 

Neutron Scattering (CHRNS)

 Joe Dura, Julie Borchers, and 

Brandi Toliver

 John Pisanic