Emulsions and Emulsion Stability Dec 19 09

1Skin Care Cosmetic EmulsionsSkin Care Cosmetic Emulsions

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Ampa Jimtaisong, Ph.D.Ampa Jimtaisong, Ph.D.School of Cosmetic ScienceSchool of Cosmetic ScienceMae Fah Luang UniversityMae Fah Luang University

December 19, 2097

OutlineOutline

Emulsion Overview Emulsification by Surface-Active Agents Hydrophilic-Lipophilic Balance-HLB Type of EmulsionM l iM l i

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MacroemulsionMacroemulsionMicroemulsionMicroemulsionNanoemulsionsNanoemulsionsMultiple EmulsionMultiple EmulsionPickering emulsionsPickering emulsions

Ampa Jimtaisong Mae Fah Luang University

Emulsion OverviewEmulsion Overview

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Continuous phase Disperse phase System

Gas Solid SmokeLiquid Gas Foam


Some common type two-phase systems

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q F mLiquid Solid DispersionLiquid Liquid EmulsionSolid Gas Foam

Emulsion OverviewEmulsion OverviewWhat is an emulsion? An emulsion is a mixture of two immiscible (unblendable)

substances. One substance (the dispersed phase) is dispersed in the

other (the continuous phase).

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Example: Oil in water emulsion (O/W)Oil: Dispersed phase (discontinuous,

inner, internal phase)Water: Continuous phase (outer,

external phase,)

Emulsion OverviewEmulsion OverviewEmulsification

Emulsification is the process by which emulsions are prepared.

Emulsions are thermodynamically unstable systems because the contact between oil and water molecules is

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unfavorable, and so they will always breakdown over time.


2Emulsion OverviewEmulsion OverviewEmulsification The preparation of emulsions that are

kinetically stable over a time period that is of practical use to the cosmetic industry requires the incorporation of substances known as

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stabilizers. Stabilizers can be classified according to their

mode of operation as either Emulsifiers Texture modifiers



Emulsifiers An emulsifier is a surface-active substance that,

when present at low concentration in a system, has the properties of adsorbing on to the surfaces of interfaces of the system

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altering to a marked degree the surface or interfacial free energies of the surfaces (or interfaces).

Examples: phospholipids, small molecule surfactants and solid particles.



Texture modifiers A texture modifier is a substance that either

increases the viscosity of the continuous phase (thickening agent) or forms a gel network within

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the continuous phase (gelling agent).

The texture modifiers help slowing down the movement of droplets due to gravity or Brownian motion.


Emulsion OverviewEmulsion OverviewTexture modifiers Most of the texture modifiers form hydrated lyophilic

colloids (called hydrocolloids) that form multimolecular layers around emulsion droplets.

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Multimolecular Film

Emulsion OverviewEmulsion OverviewTexture modifiers Hydrocolloid type stabilizers have little or no

effect on interfacial tension, but exert a protective colloid effect, reducing the potential for coalescence by

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potential for coalescence, by Providing a protective sheath around the droplets Imparting a charge to the dispersed droplets (so

that they repel each other) Swelling to increase the viscosity of the system (so

that droplets are less likely to merge)


Emulsion OverviewEmulsion OverviewTexture modifiersHydrocolloid modifiers may be classified as :

Vegetable derivatives, e.g., acacia, tragacanth, agar, pectin, carrageenan, lecithin.

Animal derivatives, e.g., gelatin, lanolin,

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g gcholesterol

Semi-synthetic agents, e.g., methylcellulose, carboxymethylcellulose

Synthetic agents, e.g., Carbopols


3SurfaceSurface--Active AgentsActive Agents

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Emulsification by Surface-Active Agents

Interface-a boundary between any two immisciblephases.

Surface an interface where one phase is a gas, usually an air.

Interfacial free energy the minimum amount of work required to create the interface

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work required to create the interface. The interfacial free energy per unit area-what

we measure when we determine the interfacial tension between two phases surface (interfacial) tension.



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Surface (interfacial) tension is the minimum amount of work required to create unit area of the interface or to expand it by unit area.

Surface (interfacial) tension is also a measure of the difference in nature of the two phases meeting at the

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p ginterface (or surface).

The greater the dissimilarity in their nature , the greater the surface (or interfacial) tension between them.



Surface tension of liquid-a measure of the interfacial free energy per unit area of the boundary between the liquid and the air above it.

When we expand an interface, therefore, the minimum work (Wmin) required to create the additional amount of th t i t f i th d t f th i t f i l t i

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that interface is the product of the interfacial tension (l) and the increase in area of the interface (A) ;

Wmin = l x A



A surface-active agent is, therefore, a substance that at low concentration adsorbs at some or all of the interface in the system and significantly changes the amount of work required to expand those interfaces.

To reduce the interfacial tension & thereby promote

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To reduce the interfacial tension & thereby promote droplet formation (the free energy increase of forming new surface is directly proportional to the interfacial tension)

To stabilize emulsion droplets from flocculation & coalescence


4Emulsification by Surface-Active Agents

General Structural features and Behavior of Surface

Active Agents: Amphipathic structure

A lyophobic group: very little attraction to the solvent

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A lyophillic group: strong attraction to the solvent.



General Structural features and Behavior of SurfaceActive Agents: Amphipathic structure

Surface-active agent dissolves in water solvent, the lyophobic (hydrophobic) group distorts the structure of water (by breaking hydrogen bonds between the water

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water (by breaking hydrogen bonds between the water molecules and by structuring the water in the vicinity of the hydrophobic group), resulting in, some of the surface-active agents are expelled to the interfaces of the system, with their hydrophobic group oriented so as to minimize contact with water molecules.



General Structural features and Behavior of SurfaceActive Agents: Amphipathic structure The surface of the water molecule become covered

with a single layer of the surface-active agent molecules with their hydrophobic groups oriented

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mo cu s w th th r hy ropho c groups or nt predominantly to the air.

Air is nonpolar in nature, same as hydrophobic group-decrease in the dissimilarity of the two phases contacting each other at the surface resulting in a decrease in surface tension of the water.




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24Critical Micelle Concentration

5Emulsification by Surface-Active Agents

25(a) Spherical (b) disk (c) Rod (d) reversed

Emulsification by SurfaceEmulsification by Surface--Active AgentsActive Agents


In a highly polar solvent such as water:Lyophobic (hydrophobic) group may be hydrocarbon

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Lyophobic (hydrophobic) group may be-hydrocarbon, fluorocarbon, siloxane chain.

Lyophilic (hydrophilic) group may be-ionic or highly polar groups.



Surfactants as Emulsifying Agents Regardless of their classification, all emulsifying

agents must be:

Chemically stable in the system,

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Chem cally stable n the system,

Inert and chemically non-reactive with other emulsion components,

Nontoxic and nonirritant.

Reasonably odorless and not cost prohibitive.


An emulsifier is a type of surfactant typically used to keep emulsion (mixtures of immiscible fluids) well dispersed.

Surfactants typically have a hydrophobic (water-hating) and a hydrophilic (water-liking) end.

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Surfactants are classified asClass Example Charge

Anionic Soap: RCOO-Na+ (e.g., Sodium stearate)Alkylbenzene sulfonate: RC6H4SO3-Na+

Negative

Cationic Salt of a long-chain amine: RNH3+Cl-

Quaternary ammonium chloride: RN(CH3)3+Cl-Positive

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Quaternary ammonium chloride RN(CH3)3 Cl

Nonionic Monoglyceride of long-chain fatty acid:RCOOCH2CHOHCH2OHPolyoxyethylenated alkylphenol: RC6H4(OC2H4)xOHPolyoxyethylenated alcohol: R(OC2H4)xOH

None

Amphoteric Long-chain amino acid: RN+H2CH2COO-

Sulfobetaine : RN+(CH3)2CH2CH2SO3-Variable


Criteria for Surfactant Selection

Hydrophilic surfactant O/W emulsion

Lipophilic surfactant W/O emulsion

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Compatibility

Give stable emulsion at low concentration

Use combination of surfactant

6HLBHLB

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Hydrophilic-Lipophilic Balance-HLB All surfactants have water loving part and oil loving part

Ratio of water loving part and oil loving part balance

HLB = Hydrophilic-Lipophilic Balance

The hydrophilicity and lipophilicity are different among emulsifiers and the balance between the two is called

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emulsifiers, and the balance between the two is called HLB value.

The value ranges from 0 to 20.

Low HLB soluble/dispersed in oil High HLB soluble/dispersed in H2O

Hydrophilic-Lipophilic Balance-HLB HLB is generally applied to nonionic surfactants and

used for selection of single or mixed nonionic

surfactants.

Combinations of emulsifiers can produce more stable

emulsions than using a single emulsifier with the same

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emulsions than using a single emulsifier with the same

HLB number.

Matching between the HLBs of the surfactant and the

oil being emulsified.

Hydrophilic-Lipophilic Balance-HLBSurfactant HLB number and application

HLB range Main application

1.5-3 Anti-foaming agents

4-6 W/O emulsifiers

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7-9 Wetting agents

8-18 O/W emulsifiers

13-15 Detergents

15-18 Solubilizers

Hydrophilic-Lipophilic Balance-HLBThe appearance of the Surfactant when added to

water is indicative of it likely HLB value.

Appearance in water HLB Value

Non-dispersed 1-4

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Poorly-dispersed 3-7

Milky 7-10

Translucent 10-13

Clear 13+

Hydrophilic-Lipophilic Balance-HLB HLB Calculation: Griffin's method

HLB = 20 * Mh / M

Mh is the molecular mass of the hydrophilic portion of the Molecule,

M is the molecular mass of the whole molecule

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M is the molecular mass of the whole molecule,

7Hydrophilic-Lipophilic Balance-HLB HLB Calculation: Griffin's method

Calculations of Molecular Mass

Molecular masses of chemical compounds are equal to the sums of the molecular masses of all the atoms in one molecule of that compound.

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H2O = (2 H x atomic mass) + (1 O x atomic mass)

= ( 2 x 1) + ( 1 x 16) = 18 g/molCH3OH =

(-CH2-CH2-O-) =

(atomic weight of C, H , O = 12 , 1, 16 g/mol, respectively)

Hydrophilic-Lipophilic Balance-HLB HLB Calculation: Griffin's method

Water-wetting and oil-wetting power

Alkyl chain coupled to polyoxyethylene chainCH3(CH2)16CH2 (OCH2CH2)nOH

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HLB = % weight content of hydrophilic part of the molecule

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If n = 3, HLB = 7.4

If n = 20, HLB = 15.6

Hydrophilic-Lipophilic Balance-HLB HLB Calculation: Determination of Required HLB Sorbitan monostearate HLB = 4.7 (A) @50 %

Polyoxyethylene sorbitan monostearate HLB = 14.9 (B) @ 50 %

HLB = xA +(1-x)B

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HLB of the mixture of emulsifying agents = ?

Hydrophilic-Lipophilic Balance-HLB HLB pros and cons Positives

-Excellent starting point-Generally produces a fairly good emulsion

Negatives, Ignores the importance of: Electrical double layer

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y Temperature effects of ethoxylates % of emulsifier to be used Phase volume ratios Component interactions

Type of EmulsionType of Emulsion

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Type of Emulsion

Oil-in-Water Emulsion

Water-in-Oil Emulsion

Multiple Emulsion

MacroemulsionNanoemulsion Microemulsion

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8Type of Emulsion Macroemulsion: particle size > 400 nm (0.4 m). Nanoemulsion (miniemulsion): particle size 100-400 nm. Microemulsion: particle size < 100 nm (0.1 m). The appearance of the emulsion is dependant upon the

particle size of the discontinuous phase. Particle size (nm) Size Appearance

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Particle size (nm) Size Appearance---------------- -------------> 400 White100-400 Blue White 400 nm-white opaque milky/cream.

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HLB value of emulsifiers used The quantity of emulsifier used the higher the

level of the emulsifier, the smaller the dispersed phase (valid only for suitable HLB emulsifier used)


9MacroemulsionsMacroemulsionsFormation Order of mixing- the phase of the emulsion which is

added to the other, often forms the dispersed phase. For example : adding Oil into Water O/W emulsion

is likely to be formed.

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Formation The phase-ratio -> the phase that is present in the

largest amount tend to be the continuous phase.

Phase-ratio favor HLB emulsifier Emulsion type

MacroemulsionsMacroemulsions

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W/O ( if less water) O/W O/W

O/W (if large water) W/O O/W

MacroemulsionsMacroemulsionsPhase Inversion Temperature: PIT As the temperature increases, the water solubility of

ethoxylated nonionic emulsifiers becomes poorer (the HLB decreases).

There is a temperature (PIT) at which the hydrophilic and lipophilic characteristics of the emulsifier are

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p pequal (relative to the required HLB of the oil phase).

At this temperature the emulsion will exhibit a phase inversion.

The PIT should be at least 20 C higher than the storage temperature.


MicroemulsionsMicroemulsions Microemulsions are transparent dispersions containing

two immiscible liquids with particles of 10- 100 nm (0.01-0.1 m) diameter that are generally obtained upon mixing the ingredients gently.

Microemulsions may be O/W or W/O. Large amounts of two immiscible liquids (e g water and

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Large amounts of two immiscible liquids (e.g. water and oil) can be brought into a single phase (macroscopically homogeneous but microscopically heterogeneous) by addition of an appropriate surfactant or a surfactant mixture.


MicroemulsionsMicroemulsionsTechnical differentiation between emulsions & microemulsion systems

Macroemulsion Microemulsion

Thermodynamically unstable Thermodynamically stable

Direct oil/water contact at the No direct oil/water contact at the

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interface interfaceMultiple phase only May be single or multiple phase

Cloudy colloidal systems Optically transparent (Isotropic)

MicroemulsionMicroemulsion

The essential distinction between macroemulsion and microemulsion is their particle size and stability.

The macroemulsion is kinetically stable

The microemulsion is thermodynamically stable.

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The stability of the microemulsion can be influenced by addition of salt, other additives, temperature or pressure.


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Microemulsions can be prepared by controlled addition of lower alkanols (butanol, pentanol and hexanol) to milky emulsions to produce transparent solutions comprising dispersions of either water-in-oil (w/o) or oil in water (o/w) in nanometer or colloidal dispersions

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oil-in-water (o/w) in nanometer or colloidal dispersions.

Microemulsion formulation will result in a faster uptake into the skin.



The emulsifying agent is generally 15- 30 %.

Cost and safety

Appropriate selection of ingredients (i.e. surfactants, cosurfactants oils) are key factors in the formulation

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cosurfactants, oils) are key factors in the formulation of microemulsions.


Nanoemulsions Nanoemulsions Nanoemulsions or miniemulsions or finely dispersed

emulsions or ultrafine emulsions.

The preparation of nanoemulsions requires high-pressure homogenization.

They are blue white semiopaque emulsion of 100 nm-

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400 nm drop size.

The emulsifying agent is generally 1- 3 % of the oil phase.


Nanoemulsions Nanoemulsions

The emulsifying agents, mixture of: Ionic surfactant and long-chain alcohol

cosurfactant The chain length of cosurfactant is at least 12

carbons

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O/W type Surfactant + cosurfactant + water = micelle Oils added Breakdown of the formed micelle to tiny droplets


Evaluation of Emulsion TypeEvaluation of Emulsion Type Electrical conductivity

Electrical conductivity of O/W emulsions is higher than that of W/O emulsions

Dilution method Evaluated the emulsion type from the dispersion

t dil ti ith t

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ease at dilution with water Dye method

Evaluated the emulsion type by dissolving water-soluble and oil-soluble dyes in the emulsion


Evaluation of Emulsion TypeEvaluation of Emulsion Type

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volume fraction of the discontinuous phase.

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Multiple EmulsionMultiple Emulsion

Water-in-Oil-in-Water type

Oil-in-Water-in-Oil type

O/W type W/O type

Oil in water Water in oil

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W/O/W O/W/O

Improving the stability of

multiple emulsions is the main

issue for the systems

Multiple EmulsionMultiple EmulsionPreparation of Multiple Emulsions by two-step method

Step 1 W/O emulsion

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Multiple EmulsionMultiple EmulsionStep 1 Preparation of primary emulsion W/O

Dropwise addition of the aqueous phase into oil phase, which contains the hydrophobic surfactants

High shear rate homogenizer may apply to obtain an internal phase size about 1-3 microns.E l

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Example composition: Brij 92 10 % Mineral oil 60% NaCl 0.3% Water to 100%


Multiple EmulsionMultiple EmulsionPreparation of Multiple Emulsions by Two-step Method

Step 2 W/O/W emulsion

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Multiple EmulsionMultiple EmulsionStep 2 Preparation of W/O/W

The primary W/O is added dropwise to a water phase, which contains the hydrophilic surfactants.

Low shear homogenizer must be applied to obtain much larger droplet.

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g p Example composition: Span 80-Tween 20 5 % Primary W/O emulsion 20% Water 75%


Multiple EmulsionMultiple EmulsionEffects of Emulsifiers on W/O/W emulsion The optimal HLB value of primary emulsifier is in the

range of 3-7. The HLB value for secondary emulsifier is 8-16. The emulsifier concentration and emulsifier ratio are

f t ff t th f ti f t bl W/O/W

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of great effects on the formation of stable W/O/W emulsion.

The primary emulsifier can migrate to the external oil phase and it may interact with the secondary emulsifier, therefore, altering the optimal HLBinstability?


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Multiple EmulsionMultiple EmulsionEffects of Emulsifiers on W/O/W emulsionExample: W/O/W multiple emulsion containing Span 83 and Tween 80a

Span 83 HLB 3.7 , the optimum concentration is 20 %

Tween 80 HLB 15, the optimum concentration is 0.1 %

High Span 83 concentrations increased the storage

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pmodulus G (solidlike) values and hence enhanced multiple emulsion stability.

Higher concentration of Tween 80 had a destructive effect on W/O/W emulsion stability


a J. Jiao, D. J. Burgess, AAPs Phama. Sci. , 5, 1,2003

Multiple EmulsionMultiple EmulsionEffects of Emulsifiers on W/O/W emulsion

Example:W/O/W multiple emulsion containing Span 83 and Tween 80a

Photomicrographs of freshly prepared W/O/W emulsion

(A) 0.1% Span 83 (B) 1.0% Span 83

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containing 0.1% w/v Tween 80 in the outer continuous aqueous phase, and various amounts of Span 83 in the oil phase (C) 5.0% Span 83 (D) 20% Span 83

Multiple EmulsionMultiple EmulsionEffects of Emulsifiers on W/O/W emulsion

Example:W/O/W multiple emulsion containing Span 83 and Tween 80a

Photomicrographs of stability of W/O/W emulsions containing 0 1% / T 80 i

(A) 5% w/vSpan83, fresh (B) the same emulsion @16 months room temp.

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0.1% w/v Tween 80 in the outer continuous aqueous phase, and 5% wt/vol Span 83 20% wt/vol Span 83 in the oil phase

(C) 20% w/v Span 83, fresh (D) the same emulsion @ 16 months room temp.

Pickering emulsionsPickering emulsions aa

The role of particles in stabilizing emulsions

The person credited with first investigating particle stabilization in emulsions is Pickering S.U.

Particles more wetted by water than oil, stabilized O/W emulsions by residing at the interface

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O/W emulsions by residing at the interface.

From this report, the term Pickering emulsions has been given to emulsions stabilized by solid particles.

a Hunter TN et al., The role of particles in stabilizing foams and emulsions, Adv Colloid Interface Sci (2007), doi:10.1016/j.cis.2007.07.007

Pickering emulsionsPickering emulsions The role of particles in stabilizing emulsions a

Conditions giving particle contact angles ( measured through the aqueous phase) slightly below 90resulted in O/W emulsions

Conditions giving slightly above 90 W/O emulsions

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Conditions giving slightly above 90 , W/O emulsions were formed.

Interestingly, conditions giving extreme contact angles (close to 0 or 180) no stable emulsions were formed.


Pickering emulsionsPickering emulsionsThe role of particles in stabilizing emulsions

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O/W W/O

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Pickering emulsionsPickering emulsions The role of particles in stabilizing emulsions a

There have been a number of different particle types used as stabilizers in both O/W and W/O emulsions, including silica, metal oxides and sulphates, and clays

The effectiveness of a specific particle type in

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stabilizing an emulsion, depends on the emulsion medium, the particle shape and size, particle wettability and inter-particle interactions.


Pickering emulsionsPickering emulsionsThe role of particles in stabilizing emulsions

Unlike surfactants, particles do not affect emulsion stability by significantly reducing the oilwater surface tension.

For successful stabilization, it is necessary that the

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particles be approximately orders of size smaller than the droplets, for the particles to be properly located around the droplets.


Pickering emulsionsPickering emulsions

The role of particles in stabilizing emulsions

Particle-stabilized emulsions seems to be of great value in the formulation of sun care products.

If such products use physical sun screen substances,

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e.g. TiO2 or ZnO, these physical filters can be distributed uniformly and they can act concurrently as emulsion stabilizers.


Pickering emulsionsPickering emulsions The role of particles in stabilizing emulsions Examples of particulate emulsifiers

Compound Emulsion Type Stabilized

Alumina W/OBetonite O/W

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Magnesium Aluminum Silicate O/WMagnesium Oxide W/OMagnesium Trisilicate W/OTitanium Dioxide (coated) O/W, W/OSilica O/W

References1. J. B. Wilkinson, R. J. Moore, Harrys Cosmeticology, 7th ed. Chemical

publishing, New York, USA, 1982.

2. S. Magdassi, E. Touitou, Novel Cosmetic Delivery Systems, Marcel Dekker, Inc., New York, NY, USA, 1999.

3. J. Knowlton, S. Pearce, Handbook of Cosmetic Science and Technology, 1st ed., Elsevier Advanced Technology, 1993.

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1 ed., Elsevier Advanced Technology, 1993.

4. M. J. Rosen, ed., Surfactants and Interfacial Phenomena, 3rd ed., John Wiley& Sons, Incorporated, NJ, USA, 2004.

5. A. Kogan, N. Garti, Advances in Colloid and interface Science, 123-126, 369-385, 2006.

Periodic table

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Emulsions and Emulsion Stability Dec 19 09

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