1. Effect of pH on the Rheology of a Liquid Crystalline Interface from Crude Oil Emulsion Fractions Isabela Soares, Angela Duncke, Angel da Silva, Carla Barbato e Márcio Nele

2. Motivation
From Biology
Crude oil
From Industry
Food

3. Introduction Lamellar liquid crystals (LC)
Surfactant bilayer;
Surrounding the emulsion droplets;
Increases emulsion stability
The relevance of LC in crude oil emulsions still under debate.

4. Purpose of the Study
Verify the influence of pH on the interfacial elastic modulus of systems able to form LC

5. Background What exactly is interfacial rheology?
Interfacial rheology explores rheological properties directly at the interphase as a two-dimensional approach (Bulk: 3D aproach)
Dilatacional x Shear
Changes in shape at constant area
Dilatacional
Shear
Changes in surface area with constant shape

6. Basic Equations and Models
Interfacial rheology can be consideraded as analagous to bulk rheology
Viscoelastic interfaces
Shear stress
Shear viscosity
Shear rate
Expansion of the interface at a constant area
Dilatacional
viscosity
Spring: elastic behaviour
Dashpot:
plastic behaviour

7. Dilatacional Measuring Thecniques
Tensiometer TECLIS Tracker- H
Computer (Software)
Sample (syringe)
Quartz cuvette
Camera CCD

8. Dilatacional Measuring Thecniques
Laplace equation and modeling
Theoretical profile

9. Dilatacional Measuring Thecniques
Interfacial rheology (Area/Volume dilatation)
Interfacial Modulus (ε)
Input -> Interfacial area/volume dilatacion
Output -> Interfacial Tension
ε‘ – Real part
ε‘’ - Imaginary part
Volume profile test
Area profile test
Possible profiles

10. Dilatacional Measuring Thecniques - Sinusoidal
The oscilations provide the interfacial rheology data: total elastic modulus (mN/m)
Active cycles (s)
Area mm²
Blank cycles (s)
To performe a test:
Density (both phases)
Volume of the drop
Period
Amplitude
# Active/blank cycles
Total time
Time (s)
* Blank and active cycles depend on the oscilation period (T)

11. 5 Active Cycles selected 5* 10s = 50s
30 Blank Cycles
30* 10s = 300s
Total periodic range: = 350s

12. Materials Crude oils = A or B Deionized water (pH 7)
NaOH solution (pH 10)

13. Methods Interfacial rheology experiments Emulsions
Tracker-H Teclis Tensiometer
Oscillating test: Volume Profile Type
Maximum oil droplet size : 70 µL
Droplets (water) : 90 % (± 63.0 µL)
Droplets (NaOH solution) : 60% (± 43.0 µL)
Oscillation amplitude : 6% of the total volume
Total time: 3h (10800 s)
Emulsions
Polytron 3100, 3 min at 6,000 rpm
20 wt.% of oil A or B + 80 wt.% of water or NaOH
Polarized light microscopy at Axiovert 40 MAT (Carl Zeiss)

14. Results and Discussion
Oil A
Oil B
Acid Number (mg KOH/g)
2.8
1.2
Density (g/cm³)
0.94
0.92
Tension
(mN/m)
pH 7
21.17
15.46
pH 10
12.45
14.11
Elastic Modulus (mN/m)
14.8
11.4
19.5
11.6

15. Results and Discussion
Oil A
pH 10
pH 10
pH 7
pH 7
ε‘’ ~ 0

16. Results and Discussion
Oil B
pH 10
pH 10
pH 7
pH 7
ε‘’ ~ 0

17. Results and Discussion
Water pH 7
NaOH pH 10
NaOH pH 12
Oil A
Oil B

18. Conclusions
The acid number (related with naphthenic acid content) is an important factor for LC formation.
Higher pHs conditions, the crude oils systems present a more rigid film and more liquid crystals structures.
Acid Number
Liquid Crystals pH

19. Acknowledgement
To Petrobras, CNPq and CAPES.