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RELATIONSHIP BETWEEN RHEOLOGICAL BEHAVIOUR AND THE TYPE OF FORMED

MESOPHASE WHEN PREPARING NANOEMULSIONS

Ronald Márquez, Ana Forgiarini, Katty Vega, María I. Briceño, Laura Márquez, Jean Louis Salager

For instance Salinity scan

Two opposite effects there is a minimum!

Formulation influences both drop break-up and the coalescence

more accurately one minimum on each side of optimum formulation!

Tens

ion!

Stab

ility!

Dro

p si

ze!

Salinity!S*! S*! S*!

O/W! W/O!

minimum!+! minimum!

MEH!

...... but in different ways

Drop size versus Formulation experimental data

With liquid crystal at optimum instead of microemulsion drops do not coalesce, hence small at optimum

Microemulsion at optimum Liquid crystal at optimum

But Optimum Formulation (γ min) depends on surfactant concentration

Hence drop size depends on dilution that results in formulation changes

dilution

dilution

Emulsification by dilution = Mass transfer + formulation change

If original formulation is adequate (slightly hydrophilic surfactant)

Dilution by water of oil solution produces a formulation scan through 3 φ because of the partitioning

Close to optimum formulation > low γ = minimum drop size

Ø  High coalescencia if mesophase is µemulsion > not stable

Ø  Protection against coalescence if mesophase is LC > stable

Nanoemulsification strategy (low energy) S

WO

Lα LLC

Original oil+surfactant (microemulsion or LC)

LαLLC swells

LαLLC breaks

nanodroplets

2 phases water penetrates in LC

Dilution Path

Inversion + mass transfer change in formulation and composition SPONTANEOUS EMULSIFICATION

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S

WO

Lα LLC

Original oil+surfactant forms LC that takes water in

LαLLC swells

LαLLC breaks

nanodroplets

2 phases

OIL

WATER

Dilution Path

Inversion + mass transfer change in formulation and composition SPONTANEOUS EMULSIFICATION

Equilibrium Ternary Diagram and dilution path through a LC

HLB 12

T = 30ºC Actually 4 mesophases were formed before an O/W emulsion was reached

original solution

Conductivity vs. Water content 4 mesophase cases

Tween 80-Span 20 (HLB=12)/Water/Paraffin Oil system at a S/O relationship of 25/75, 0.06% NaCl and T=30ºC

ü Conductivity increases

ü Posible phase transitions

Droplet Size and Rheology Relationship

O+LC

O+LC+Wm

Drop Size O+LC mesophase

O+LC+Wm mesophase

The rigidity of the liquid crystalline phase in the O+LC+Wm region makes difficult the formation of fine droplets

in the O+LC region the lamellar liquid crystalline phase initially formed releases oil and decreases the rigidity of the mesophase

ü  x > Rigid LC

Rheology (G’/G”)

O+LC

O+LC+Wm

Conclusions

Phase Inversion Emulsification by dilution shows a relationship between

Ø  rheological behavior, Ø  type of mesophase formed Ø  droplet size of final emulsion

Viscoelasticity measurements allow to distinguish the phase transition between the O+LC and O+LC+Wm cases This is important because … nanoemulsions are only attained with O+LC mesophase slowly produced, then quickly diluted.

S

WO

LC