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Microemulsions

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brine/oil ratio. surfactant/oil ratio. M Wt. of surfactant. Manipulating ... Surfactant formulation- surfactant, alcohol and brine with or without added oil. ... – PowerPoint PPT presentation

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Title: Microemulsions


1
Microemulsions
2
Microemulsions
  • Microemulsions are thermodynamically stable,
    optically transparent, isotropic dispersions of
    aqueous and hydrocarbon liquids stabilized by an
    interfacial film of surfactant molecules
  • Microemulsions are monodispersed spherical
    droplets (diameter lt 100 nm) of water in oil or
    oil in water, depending on the nature of the
    surfactant.

3
Microemulsions and (Macro) emulsions are Different
4
Formation of Microemulsions
DGm free energy change for microemulsion
formation DG1 free energy change due to
increase in total surface area DG2 free energy
change due to interaction between droplets DG3
free energy change due to adsorption of
surfactant at the oil/water
interface from bulk oil or water DS increase
in entropy due to dispersion of oil as droplets
Ruckenstein, E, Chi, J. C., Faraday Trans. II
71 (1975) 1690.
5
Stability of MicroemulsionsWhy are
microemulsions thermodynamically stable?
?Gm gt 0 for C D ? emulsion formation
ve
? Gm ? G1 ? G2 ? G3 - T?S
Unstable
0
Stable
-ve
?Gm lt 0 for A B in certain R range
? microemulsion formation in that R range
NOTE Microemulsions form spontaneously only when
IFT is small. (order of 10-3 mN/m)
Ruckenstein, E, Chi, J. C., Faraday Trans. II
71 (1975) 1690.
6
Watch the apparent dichotomy !
The Young Laplace Equation predicts an inverse
relation of pressure drop with droplet radius
Further, free energy arguments should predict, a
rapid coalescence of droplets that are lt 100 nm
Then why are microemulsions thermodynamically
stable?
7
Microemulsions are formed because ...
  • The penalty for the apparent increase in free
    energy is compensated by the lowering of IFT to
    ultra low levels (10-2 10-3 mN/m)
  • The work done in lowering IFT is achieved through
    a gain in system entropy ?S due to the creation
    of a large number of sub-micron sized droplets

All this occurs when at molecular levels,
surfactants form the most condensed interfacial
film between oil and water
8
Microemulsions form when CPP 1
The most condensed interfacial film between oil
and water is formed when maximum number of
surfactants pack Occurs when surfactants orient
vertically !
9
Formulating Microemulsions Bancrofts rules
(CPP lt 1) O/W emulsion
(CPP gt 1) W/O emulsion
Change in variables (T, Salting out electrolyte
etc.)
10
Formulating Microemulsions Bancrofts rules
Surfactant
3 phase domain (oil - ?E -water)
(Bicontinuous ?E)
1 phase microemulsion
Water
Oil
W/O or O/W microemulsion
CPP 1
Sometimes, a co-surfactant such as a short chain
alcohol is used in conjunction with the
surfactant to facilitate condensed interfacial
film formation
11
But! Watch what we just did !
Surfactant
3 phase domain (oil - ?m -water)
(Bicontinuous ?E)
1 phase microemulsion
Water
Oil
W/O or O/W microemulsion
CPP 1
We just happened to bring OIL AND WATER, 2
IMMISCIBLE LIQUIDS, INTO 1 SINGLE PHASE
See the Potential for Enhanced Oil Recovery?
12
Tracking phase change using test tubes
Surfactant
Surfactant
Surfactant
Water
Oil
Water
Oil
Water
Oil
T3
T1
T2
13
Some Definitions / Conventions
Surfactant
Surfactant
Surfactant
Water
Oil
Water
Oil
Water
Oil
T3
T1
T2
Winsor I
Winsor II
Winsor III
Lower phase ?E
Middle/ 3 phase ?E
Upper phase ?E
14
Manipulating Micro-Emulsions
Variables to play with
  • Salinity
  • Oil chain length
  • Alcohol conc.
  • Temperature

Total surfactant brine/oil ratio surfactant/oil
ratio M Wt. of surfactant
15
Interfacial Tension with Salinity
16
Solubilization
  • For middle phase microemulsion,
  • 1 mol CaCl2 ? 16-19 moles of NaCl
  • and for oil-external microemulsions,
  • 1 mol CaCl2 ? 4 moles of NaCl
  • Values of optimal salinity
  • LiCl gt NaCl gt KCl gt NH4Cl
  • At phase inversion, partition coefficient is
    near unity.
  • Repulsion forces between micelles decreases due
    to the neutralization of surface charge of
    micelles by counterions.

17
Enhanced Oil Recovery by Microemulsion Flooding
  • Proper selection of chemicals in formulating the
    surfactant slug.
  • Surfactant formulation- surfactant, alcohol and
    brine with or without added oil.
  • Correlation between interfacial tension and
    interfacial charge.

18
Enhanced Oil Recovery by Microemulsion Flooding
Vol. fraction of middle phase
TRS 10-410 wt.
  • Even at very low surfactant concentration,
    microscopic amount of middle phase remains.
  • Oil recovery maximum near the optimal salinity of
    the system.

19
Enhanced Oil Recovery by Microemulsion Flooding
  • For high salinity reservoirs, mixed surfactants
    are promising for enhanced oil recovery.
  • Electrophoretic Mobility Maximum mobility
    corresponds to minimum in interfacial tension at
    the crude oil/caustic interface.
  • Transient Processes
  • At optimal salinity
  • Fastest coalescence occurs
  • Minimum in pressure jump
  • Minimum in apparent viscosity

20
  • Various phenomena occurring at the optimal
    salinity

21
Production of Complex Oxides/ nanoparticles
through microemulsions
  • W/O microemulsions provide a novel vehicle for
    synthesis of a micro-particulate oxalate
    precursor which yields very high density sintered
    pellets of YBa2Cu3O7-x.
  • Steric barrier by surfactant monolayer restricts
    the growth of precipitated particles and hinders
    intergrain coagulation.

22
  • Schematic of W/O microemulsion and the reaction
    mechanism

23
Microstructure of microemulsion method synthesis
  • Microstructures of sintered YBa2Cu3O7-x
  • prepared by W/O microemulsion

Microstructures of Pd, Pt nanoparticles
prepared using W/O microemulsion
24
Drug Detoxification by Microemulsion
Drug
25
Test on Isolated Guinea-pig Heart
26
Experiment Detail Measured QRS intervalInfused
Bupivacaine (5 µM) to cause cardiotoxicity (QRS
prolongation 20 msec)
Test on Isolated Guinea-pig Heart
R
Q
S
2) Bupivacaine
1) Control
3) Bupivacaine ME
27
Isolated Guinea Pig Heart - Results
28
De-Emulsification
  • Cotton, wool, glass fibers and teflon to promote
    coalescence
  • Addition of acid/base neutralizes the particle
    charge and leads to coagulation
  • Application of high voltages
  • Heating of emulsion.
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