cosmetics and physical chemistry - mae fah luang...

Nattaya Lourith, Ph.D. 1

Cosmetics and Physical Chemistry

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Lecture plan

+ Formulation Chemistry+ Physical property+ Rheology+ Colloids and Interface Science+ Emulsion

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Cosmetics- Compounds mixing- Desired characteristics mixture

Formulation Chemistry 4

FormulationMeasurement

- Liquids by volume- Solids by weight

Without any chemical equation being written down

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Particular more profitable cosmetics

+ non-allergenic formulations+ longer duration wearability

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Chemical Principles- Thermodynamics of mixing- Phase equilibria- Solutions - Surface Chemistry- Colloids- Emulsions- Suspensions

+ Adhesion

+ Weather resistance

+ Texture

+ Shelf life

+ Biodegradability

+ Allergenic response

Etc.


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AppearanceColorOdorpHViscositySurface and Interfacial TensionCloud Point

Physical property

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pH

9Visible Light

Red

Orange

Yellow

Green

Blue

Indigo

Violet

R

O

Y

G

B

I

V

700 nm

650 nm

600 nm

550 nm

500 nm

450 nm

400 nm

Color

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Journal of Fluid Mechanics, 429, 381-390, (2001).

Fluid

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FIG. 1. Formation of the chain of large bubbles in a very viscous mineraloil polymer solution

FIG. 2. Fast formation of the chain of bubbles in 2% methocel solution in waterFIG. 3. Chain of bubbles in 2% methocel solution in waterFIG. 4. Chain of bubbles in hand soap contain methocel

Physics of Fluids, 14, 3375-3379, (2002).12

Rheology


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Rheology = Viscosity + Elasticity

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Newtonian fluid

Hookian body

15Viscoelastic body 16

Flui

d be

havi

ors

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New

toni

an f

luid

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Non-Newtonian fluid


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Viscosity

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Fluid behavior

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Newtonian fluid and viscosity

Exp. Water

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Non-Newtonian fluid and viscosity

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Exp. Toothpaste

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Hysteresis loop

Exp. Lotion & Shampoo

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Colloid and interface scienceColloid

colloid (Greek for glue-like)- Thomas Graham, 1861- pseudosolution- 10-9-10-6 m

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Colloid and interface science

Colloids and dispersion- dispersion medium

+ gas+ liquid+ solid

- disperse phase+ molecular form+ ionic form 30

Dispersion system3 types based on particle size

- molecular+ molecules or ions up to 1 nm

- colloidal+ 1 - 1,000 nm

- coarse

+ 1,000 nm (1 µm)


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3 types based on disperse particle’s properties- molecular colloids

: macromolecular solution : thermodynamically stable true solution

- association colloids: small molecules and ions solution : MICELLES :

thermodynamic equilibrium truly stable system

- disperse colloids: thermodynamic unstable system with multiphases

Dispersion system

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Disperse colloids

Sponge Pomade, gelatin jellyColored glass

XerogelGel Solid colloid

Gas Liquid Solid

Solid

Shaving foamMilky lotionNail enamel

Foam Emulsion Suspension

Gas Liquid Solid

Liquid

-SpraysPowder, sprays

-Aerosol Aerosol

GasLiquid Solid

Gas

Exp.Exp.namenamephasephasemedium

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Colloid in cosmetics≡≡ Lotions (Lotions (o/wo/w) : high viscosity at low shear rate) : high viscosity at low shear rate≡≡ Hand creams (Hand creams (o/wo/w or w/o) : high viscosity at high or w/o) : high viscosity at high

shear rate; bodyshear rate; body≡≡ Lipsticks (suspension) : Lipsticks (suspension) : viscoelasticviscoelastic solidsolid≡≡ Nail polishes (suspension) : Nail polishes (suspension) : thixotropicthixotropic≡≡ Shampoos (gel) Shampoos (gel) ≡≡ Antiperspirants (suspension) : shear thinning Antiperspirants (suspension) : shear thinning ≡≡ Foundations (suspension Foundations (suspension –– emulsion): emulsion): thixotropicthixotropic

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Interface

A – molecules attracted in all directions

B – molecules being attracted inwards only

Boundary between 2 phases

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Interfacial tension

Surface tension : one of two phases is vapour or vacuum

Interfacial tension : more comprehensive

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Cosmetics- adsorption- emulsification- wetting- foaming

Interface phenomena


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Interfacial tensionγs : solid – air

γl : liquid – air

γsl : solid – liquid

cosθ = (γs - γsl)/γl

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Interfacial tension

ϕ = 0° ϕ < 90° ϕ = 90° ϕ >90° ϕ = 180°

γs - γsl > 0 γs - γsl = 0 γs - γsl < 0

Wetting

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Surfactant : Micelles40

Micelles

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Micelle forms

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Soap and interfacial tension

Grease on surface Greasy surface immersed

in soap solution

Grease surrounded by soap molecule film forming a globule

The grease globule separates from the surface with agitation


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Emulsion types

oil-in-water (o/w)- creamy texture

- a much higher electrical conductivity

water-in-oil (w/o)- greasy

Greater phase volume need not necessarily be the dispersion medium

> 74% there is either a phase inversion or the droplets are deformed to polyhedra

Polyhedral cells

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Macroemulsions droplet i.d. > 10 µm

Miniemulsions 0.1 > droplet i.d. > 10 µm

Microemulsionsdroplet i.d. < 100 nm

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Emulsifier & System

o/w, w/oMicroemulsionsMacroemulsionsBilayer dropletsDouble and multiple emulsionsMixed emulsion

Nonionic surfactantsSurfactant mixturesIonic surfactantsNonionic polymersPolyelectrolytesLiquid crstalline

Structure of the systemNature of emulsifier

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EmulsionCreaming – less dense phase risesSedimentation – greater dense phase sinks Inversion – internal phase becomes external phaseOstwald ripening – small droplets get smaller and

diffuses forming biggerFlocculation – droplet stick togetherCoalesence – droplets combine into larger ones

The most important physical properties of an emulsion is its stability

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Emul

sion

Creaming Sedimentation Ostwald ripening

FlocculationCoalesenceInversion

Emulsion

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Physical properties of emulsions

- Internal and External phases identification- Droplet size and size distributions- Concentration of disperse phase- Rheology- Electrical properties- Multiple phase emulsions


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Emulsion stability

Factors - low interfacial tension- steric stabilization - electrical double layer repulsions- relative small volume of disperse phase- narrow size distribution- high viscosity

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Emulsion inversion

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encapsulation and phase transfer of a guestmolecule by reversed unimolecular micelles

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Phase inversion temperature

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Stability enhancement• Creaming or Sedimentation

oil & water’s density matchingdroplet size reductionthickeners adding

• Flocculationhigh surfacelow electrolytes low ions valency

• Ostwald ripeningsecond disperse phasesurfactant

• Coalescence mix surfactantsliquid crystal film

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HLBHyrophilic Lipophilic BalanceWilliam C. Griffin, 1971

HLB : a relative ratio of polar and non-polar groups of amphiphilic surfactant

+ surfactant HLB

+ required HLB


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Surfactant HLBNecessary to obtained the desired emulsifying

properties

Exp. The mixture of 40% Span60 (HLB = 4.7) and 60% Tween60 (HLB = 14.9). What is the HLB of this mixture?

(4.7 × 0.4) + (14.9 × 0.6) = 10.82

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Required HLB

HLB needed for emulsification of the oil phase.

Exp. Prepare the mixture of Span80 (HLB = 4.3) and Tween80 (HLB = 15.0) with the required HLB of 12.0

[4.3 × (1-X)] + 15X = 12.0

4.3 – 4.3X + 15X = 12.0

10.7X = 7.7

X = 0.72

72% Tween80 + 28% Span80

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Exp. Of the O/W emulsion containing cetyl alcohol 15 g. , white vaseline 1 g., lanolin 2 g., glycerin 5 g. and water q.s. 100 g., calculate the required HLB.

Required HLB

Cetyl alcohol 13.0

White vaseline 10.5

Lanolin 15.0

O/W emulsion required HLB

Total oil phase = 15 + 1 + 2 = 18

Total required HLB = [15(13.0/18)] + [1(10.5/18)] + [2(15.0/18)]

= 10.83 + 0.58 + 1.67 = 13.0858

Multiple emulsions

w/o/w o/w/o

Particles as emulsion stabilizers

A : preferential wetting by water leading to o/w

B : preferential wetting by oil leading to w/o

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HLB values and applications

Anti-foaming agentsW/O emulsifiersWetting agentsO/W emulsifiers DetergentsSolubilizers

1.5 – 3 3 – 67 – 98 – 15 13 – 15 15 – 18

Application HLB range

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Variation of emulsion type


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Breaking emulsions- Chemical demulsification, i.e. change the HLB

+ add an emulsifiers of opposite type + add agent of opposite charge

- Freeze-thaw cycles- Add electrolyte, Change the pH, Ion exchange- Raise temp- Apply electric field- Filter through fritted glass or fibers - Centrifugation 62

Clou

d po

int

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Clou

d po

int

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Phase behavior

a single liquid phase at room temperature andseparates into two phases at sub-ambient

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Cloud point test

phase separation at temperatures aboveand below room temperature 66

Critical micelle concentration : CMC

The concentration at which micelles are formed


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Critical micelle temperature : CMT

Solution

Cloudpoint

C

Micelles +solution

CMC

CMT

PhaseSeparation

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Krafft Point

Crystals +solution

Tkrafft

CMC

C

Micelles +solution

Solution

Liquidcrystals

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Foam

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Foam

Dispersion of gas in a liquid where the volume fraction of the gas is larger

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Spherical bubblesWet spherical foam at 400X

Polyhedral cellsDry hexagonal foam at 400X 72

Bubbles formation

Two bubbles floating at the liquid-air interface. The pressure in the liquid at B is less than at A or A’

Plateau border between three cells in a foam. Due to the curvature of the liquid-gas interface, the pressure is lower by ΔP at the point of intersection of the channels leading to capillary flow


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Foam stability- Drainage - Coarsening - Film rupture

+ too thin and weak film foam+ collapse and vanish

: aqueous solution of short chain acids or alcohols=> unstable foam

: soap solution, detergents, saponins, etc.=> metastable foam

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Film foam stabilization

Liquid crystal

Micelle

Liquid crystals stabilize foams

Electrostatic film foam stabilization

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Foam breaking- Mechanical - Shock waves- Compression waves- Ultrasonics- Rotating discs- Heating - Electrical spark

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Antifoams

With an antifoam on one surface, electrostatic stabilization is lost.

A : antifoam drop, B : entering the surface, C : leading to film rupture

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References

Schlossman ML. (ed.) The chemistry and manufacture of cosmetics – Volume I. 3rd. Allured: Illinois, USA. 2000.

Tadros TF. (ed.) Emulsion science and technology. Wiley: Weinheim, Germany. 2009.

Tadros TF. (ed.) Colloids in cosmetics and personal care. Wiley: Weinheim, Germany. 2008.

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