Cosmetic products

1. 1-Mar-23
V N Kowshalya
Department of Chemistry
Kongu Engineering College
Perundurai

2. Cosmetics
 “Articles intended to be used by
means of rubbing, sprinkling or by
similar applications to the human
body for cleansing, beautifying,
promoting attractiveness, or altering
the appearance without affecting
structure or function and maintaining
health of the skin and hair.”

3. History of Cosmetics
•Cosmetics are becoming inevitable part of life and
used regularly by increasing number of people.
•Exact origin is unknown but archeological excavations
confirm that they were used in early stone age and
traced back to the ancient Egyptians.
•Civilizations have used cosmetics – though not always
recognizable compared to today’s advanced products.
•Cosmetics usage throughout history can be indicative
of a civilization’s practical concerns, such as
•protection from the sun,
•Protection from dryness because of cold
•Irritation from insect bites
•indication of class,
•conventions of beauty
•For spiritual belief/to ward off evil spirits

4. Modern age cosmetics
With ages, most of the purposes
disappeared.
Main purpose of using cosmetics in
modern society.
•Enhance attractiveness
•Improve self esteem
•Promote tranquility
•Personal hygiene
•Prevent ageing
•Protect skin & hair from UV,
pollutants, etc

5. Classification
Skin care cosmetics
Makeup cosmetics
Body cosmetics
Hair care cosmetics
Scalp care cosmetics
Oral care cosmetics
fragrances

6. Basic sciences of cleansing
Cleansing – remove dirt, grime and sebum from skin and
hair
Shampoos and body washes (soaps & liquids)
Basic requirement – cleanse (remove oil, dirt &
microorganisms), condition, facilitate cleansing and
fragrance.
Promoting hygiene and cleanliness have been aimed at
removing odors and the bacteria that cause these odors
from the surface of the human body.

7. Sebum glands adjacent to hair follicles emit a lipid-rich
substance called sebum.
Sebum is the semi fluid secretion of the sebaceous
glands of mammals, consisting chiefly of fat, keratin, and
cellular material.
Role of Sebum:
Sebum serves to protect and lubricate the skin and hair.
Sebaceous secretions favor the growth of facultative
anaerobes such as Propionibacterium acnes.
Hair & Skin

8.  P.acnes hydrolyses the triglycerides present in
sebum, releasing free fatty acids onto the skin.
 The released fatty acids contribute to the acidic
pH of the skin surface (5.4-5.9), which inhibits
the growth of many common pathogens such
as Staphylococcus aureus and Streptococcus
pyogenes (causes skin infections).
 Thus the presence of sebum and the symbiotic
microorganisms that it supports may be
beneficial to the health of the skin.
 However, buildup of sebum on the skin and hair
is perceived by modern consumers to be
“unclean” and undesirable.

9.  Additionally, particulate dust and dirt can adhere to the sebum
layer and this exacerbates the feeling of lack of cleanliness.
 Also the accumulation of P.acnes bacterium will result in acnes
and further causing scar on skin surface.
 Consequently, the principal aim of today’s cleansing products is
to remove oils, particulate soil, and microorganisms from the
surface of skin and hair.
 Because sebum is an oily substance, it cannot be removed by
water alone.
 For this reason, surface active agents (surfactants) are
included in personal care cleaning products.
 The main purposes of surfactants are to lower the interfacial
tension between the soil and the substrate, to emulsify and/or
solubilize oily soils, and to disperse particulate matter.

10. Surfactants
Surfactants, are wetting agents that lowers the
surface tension of a liquid, allowing easier
spreading and dispersion
Surfactants are usually organic compounds that are
amphipathic, as they contain both hydrophobic
groups ("tails") and hydrophilic groups ("heads").
Therefore, they are soluble in both oil and water.

11. Classification
 Polar hydrophilic head
 Non-polar hydrophobic tail – hydrocarbon,
fluorocarbon, or siloxane
 Classified based on their polar heads
(hydrophobic tail often similar)

13. https://youtu.be/nPIlDaAX4vE

14. surfactant = SURFace ACTing AgeNT.
 the term surfactant is not always the one that everyone sticks
with.
 It seems that surfactants have several names that all become
applicable depending of the role of the surfactant
 For example, where foam is the finished product, the surfactant
used maybe referred to as foaming agents.
 Surfactants used in body products, can even be termed as
detergents or soaps.
 Or, in the example of shaving creams, surfactants are considered
lubricants because they protect the skin from irritation and the
razor's sharp edge while still allowing the removal of all of the
unwanted hairs.

15. Surfactant and adsorption
 For aqueous phases in the absence of oil, at very low
surfactant concentrations the amphipathicity expels
surfactant molecules to the surface, a process called
adsorption.
 The driving force for surface adsorption derives from
hydrophobic interaction, which rejects the
hydrocarbon from the aqueous phase.
 The adsorbed surfactant molecules maintain intimate
contact with water at the surface as a consequence of
the relatively strong interactions between the
hydrophilic moieties and water at the surface.
 These strong interactions can be polar, ionic, Lewis
acid/Lewis base, and London dispersion forces.
 The surfactant concentration at which a monolayer of
surfactant molecule adsorbs and covers the surface is
called surface aggregation concentration.

16. Surfactant micelles
As the concentration of surfactant increases,
bilayers/multilayers are likely to form on surfaces.
Surfactant molecule can also form aggregates in aqueous
phase in such a way that they orient their hydrophobic tail
toward neighboring surfactant molecule and their
hydrophilic head towards water or hydrophilic surface.
The surfactant concentration at which surfactant molecules
start to form aggregates such as micelles in solution is
termed as critical micelle concentration(CMC).

17. How surfactant works:
https://youtu.be/F7-ie4uWX04

18.  Surface adsorption of surfactants is favored at low concentrations.
 However, above a critical concentration, CMC, the chemical
potential drive of molecules to form large micellar aggregates
becomes favored over surface adsorption.
 Micelles can assume a number of different shapes. Indeed the
same surfactant can adopt different micelle shapes depending
upon, for example, the concentration of surfactant, the pH of the
solution, or the presence of salt ions.
 Micellization is essentially a phase separation of water from oil,
the extent of phase separation is limited by the need of the
hydrophilic moieties to be in intimate contact with the aqueous
phase.

19.  Micellar shape is a consequence of
two opposing forces: the cohesion of
the core due to hydrophobic
interaction, which is limited by the
repulsion between the hydrophilic
moieties
 Thus, bulk separation is prevented and
micellar phase separation is favored
by the curvature imposed by the
repulsion between the hydrophilic
moieties at the micelle surface.

20. Decreased repulsion between hydrophobic moieties or
increased steric hindrance between hydrophobic core
molecules causes a decrease in the curvature of the
micelle structure.
The molecules must pack according to intermolecular
forces, and consequently the decrease in curvature forces
the micelles to transition in shape from spheres to elliptical
spheroids to rods to worms to packed rods (hexagonal
phase) to infinite two-dimensional layers (lamellar phase)
to inverse rods and inverse spheroids.

21. Surfactants and Cleansing
Surfactants remove oils from the skin and hair surface
by several mechanisms. There are four main
mechanisms for removing oils:
Roll-up
Emulsification
Penetration and
Solubilization.

22. Rollup Mechanism
 Rollup of the oil droplets occurs readily for oils spread on hydrophilic
surfaces.
 Surfactant adsorption on the substrate and on the oil surface causes an
increase in the contact angle of the oil at the oil-water-substrate interface.
 When the 3-phase contact angle approaches 180 degree, the resultant
interfacial force holding the oil droplet to the surface is overcome by the
wetting tension of the surfactant-covered oil and substrate surfaces, and
the oil rolls up into a droplet that lifts off from the substrate under mild
agitation.

23.  Due to the wide variation of surface energies on the skin and hair, the
rollup mechanism is not necessarily predictable.
 Moreover, the diversity on oily soils can alter the route by which the
surfactant adsorbs to the soil and the substrate.
 For example, the surfactant may adsorb by
 encroachment along the surface
 through interaction with a previously applied permeable surface
treatment, or
 by absorption into the substrate and subsequent diffusion to the
interface (bleached hair)
 The rate of rollup varies with the viscosity of the oily soil.
 Viscous or crystal-containing oils and waxes tend to rollup slowly and may
require vigorous mechanical application to become dislodged from the
substrate.

24. Emulsification Mechanism
 Emulsification is favored when the substrates are relatively hydrophobic and
adsorption of the surfactant at the oil-water interface is facile and results in a
low oil-water interfacial tension.
 The resulting low interfacial tension favors expansion of the oil-water
interface into the aqueous phase and the oil-droplet necks and emulsifies
driven by Rayleighe -Taylor instability.

25. Penetration Mechanism
 Favored by polar oils, such as sebum, or phase-separated simple
coacervates at temperatures above their lower critical solution
temperature.
 If the surfactant diffuses into the oil in sufficient concentrations, the oils
can become part of a self-assembled mesomorphic phase, such as
lamellar phase.

26.  Water layers are an essential part of these self-assembled
surfactant systems.
 Repulsion between the bilayers of a resulting lamellar phase
will cause the lamellar phase to swell and break off.
 Fresh surfactant then penetrates the newly exposed surface
and the process repeats.
 The dislodged oil becomes an emulsion stabilized by lamellar
phase.
 The penetration mechanism is especially useful in hard water
area where anionic surfactants form coacervate phases in the
presence of calcium salts.

27. Solubilization Mechanism
process of incorporating a water-insoluble
hydrophobic substance in the internal hydrophobic
core of micelles.
The kinetics of micellization and surfactant
adsorption and exchange between micelles is
important in this mechanism
1-Mar-23

28. Surfactant and Foam
 Foam is a two-phase system in which the gas (air) phase is dispersed in a small
amount of liquid (water) continuous phase.
 A bubbly foam – wet foam (e.g. in ice cream) is formed when the amount of
gas incorporated is low enough for bubbles to retain roughly spherical shape.
 Polyhedral foam – dry foam (e.g., beer foam) – the gas- to-liquid ratio is so large
that bubbles are pressed against one another in a honeycomb- type structure.
 Wet foam tends to form at the lower portion of the foam column, while dry foam
tends to form at the upper portion.
 The wet foam is more spherical and
viscous, and the dry foam tends to be
larger in diameter and less viscous.
 Wet foam forms closer to the
originating liquid, while dry foam
develops at the outer boundaries.
1-Mar-23

29.  Foaming is a cue that provides the user with evidence that the product is working to
cleanse the body, but foaming is more than a consumer-perceived sensory attribute;
foam does serve to float hydrophobic particles away from the substrate
 foaming of liquids is enabled by surfactants and characterized by their very low density.
 Large surface area confers the advantages of dust removal, but the adsorption of
surfactant from the bulk could deplete the micellar surfactant concentration and thereby
diminish cleansing by emulsification, penetration, and solubilization mechanisms.
 In such instances the need to generate a foam while achieving excellent cleansing
mandates a lower limit of surfactant concentration in the formulation.
 There are three distinct processes that should be considered when trying to understand
the basics of foams:
 foam initiation and formation
 foam stability
 foam drainage and rupture
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30. Foam Formation
 The formation of a foam initially requires the formation of large gas voids that
create enormous area of liquid-gas interface.
 Initially small spherical bubbles are imbibed in a creamy “kugelschaum” ("kugel"
means "sphere" and "schaum" means foam) .
 When the volume fraction of air increases to a limit, the liquid faces between the
bubbles distort and the foam becomes a system of air trapped in polyhedral films
(polyederschaum).
 In a pure liquid, the interfacial area is unstable and the liquid film retracts into the
bulk liquid almost as quickly as it formed.
 In surfactant solutions, the surfactant adsorbs at the surface of the liquid –
reducing surface tension and forms a film around the gas bubbles.
 This surfactant adsorption results in a surface tension gradient that creates
velocity gradient normal to the plane of the film, which creates a tension at the
interface that opposes drainage of the liquid from the film.
1-Mar-23

31.  In the case of a pure liquid, there is no preferential adsorption at the interfaces, and hence no
velocity gradient to oppose liquid drainage.
 As a result, there will be no viscous shear force opposing drainage, and the film will exhibit
plug flow (resisted only by extensional viscosity), and the draining elements will tear the film
apart.
 On the other hand, surfactant adsorption leads to a surface tension gradient that balances
the viscous forces of liquid flow, and the film becomes stable for a longer duration.
 Surface tension drives to minimize the surface area of the bubble however the excess
pressure (pressure difference between inside and outside bubble) counteracts it and an
equilibrium bubble size is reached.
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32. Foam Stability
 The stability of a foam may be measured in terms of loss of foam volume over
a period of time.
 All foams are thermodynamically unstable, due to their high interfacial energy,
which is dissipated upon rupture of the foam.
 A minimum concentration of surfactant is required to increase foam lifetime to
confer stability on the foam lamellae.
 when a surfactant is present the interfaces are essentially rigid and a
parabolic velocity profile will exist.
 Therefore, the increased viscosity will slow down drainage and collapse.
 Foam formation can be linked to dynamic surface pressure, but foam stability
seems to depend on surface dilatational rheology (interface is expanded and
contracted in a controlled manner - method for measuring the stability of
emulsions and foams).
1-Mar-23

33.  Low concentrations of adsorbed surfactants result in liquid
monolayers that are elastic.
 Expansion of the interface leads to an immediate elastic recoil that
prevents the formation of a foam.
 At higher surface excess concentrations, the surface dilatational
rheology becomes viscoelastic, and it seems that the viscous
component is necessary for foam stability.
 Dilatational viscoelasticity has been linked to the presence of
surfactant aggregates or complexes in the surface adsorbed layer
1-Mar-23

34. Foam Drainage
 During foam production the foam is predominantly in a liquid state and the
volume fraction of liquid/gas is relatively high.
 However, this liquid state is metastable, and upon cessation of foam
generation, the foam coarsens.
 Liquid drains from foam under gravity.
 Foam drains along lamellae to the curved junction of thin lamellae (plateau
borders) where the pressure is low.
 As the liquid drains, the film of bubble brought closer.
 The process of coarsening essentially entails an increase in the average
bubble size and a decrease in the lamellar distance between bubbles.
 Coarsening occurs by drainage of the liquid between the fragile
membranes of the bubbles, and diffusion of gas across the faces of liquid
films that surround the gas bubbles
 Film drainage can be slowed by increasing the viscosity of the intralamellar
liquid.
 This can be achieved by the addition of water-soluble polymers, especially
hydrophobically modified hydrophilic polymers that can interact with both
sides of the lamellae and span the channel.
1-Mar-23

35. Foam Rupture and Collapse
 A liquid of high surface tension pulls more strongly on the surrounding fluid than a
liquid of lower surface tension.
 Therefore, if a surface tension gradient is set up in a liquid, the liquid will
spontaneously flow away from the region of low surface tension.
 This can be demonstrated by sprinkling pepper on a clean water surface and then
adding one drop of surfactant solution to the center of the surface. The pepper
immediately flows to the periphery of the vessel. This is an example of Marangoni
flow.
 Marangoni flow can lead to lamellar film stability or instability.
 soap films are in a condition of pseudoequilibrium since the surface energy can be
lowered by collapse of the film into a smaller volume of unfoamed liquid.
 Fluctuations caused by air flows or convection within the film cause variations in
the film thickness.
1-Mar-23

36.  If the fluctuation causes the film to be pinched, the surface area of the pinch
point increases with respect to the rest of the film.
 This causes a transient lowering of the excess surface concentration of
surfactant, which causes a momentary increase in surface energy, which in
turn causes Marangoni-driven flow of liquid into the pinch point, which
restores the film to its original thickness, thereby stabilizing the film against
rupture.
 This process is called the Gibbse Marangoni effect, and the surface elasticity
conferred on the film to cause it to self-heal is called Gibbse Marangoni
elasticity.
 If the Marangoni flow is faster than the surface diffusion rate of surfactant, the
weak spot in the film may not be repaired, and catastrophic film failure will
result.
1-Mar-23

37. Polymers in Cosmetics
 Polymers are used extensively in cosmetic products, almost to the point of being ubiquitous.
The range of uses for polymers is diverse and, apart from packaging, polymers are used as:
 film formers in hair fixatives, nail products, mascara, and transfer-resistant makeup
 thickeners and rheology modifiers for emulsions, gels, pigmented dispersions, hair
colorants, and hair relaxers
 emulsifiers that can be stimuli responsive upon application for sophisticated skin
treatments and products such
 as sports sunscreen
 conditioners for skin and hair
 moisturizers for skin
 emollients that improve the “rub-in” characteristics of skin products
 pigment dispersers and stabilizers
 waterproofing agents
 controlled-release matrices
 foam stabilizers and destabilizers
 sensory-feel additives
 antimicrobial agents
1-Mar-23

38. Polymer Solubility and Compatibility
 In considering the use of polymeric ingredients, it is essential to understand the basis of
polymer solubility and compatibility. Regular solution theory reveals two drivers for the
dissolution of one substance in another:
 enthalpic interaction between the components; a negative enthalpy of interaction favors
dissolution
 increase in configurational entropy due to mixing of the components according to the
relationship
 As the molecular weight of the solute increases, the entropic driving forces are diminished for
dissolution of polymers.
 As a consequence, polymer solubility depends strongly on the enthalpic interaction between
the polymer and the solvent.
1-Mar-23

39. Polymer Conformation – spatial arrangement (variation in shape, size
and positioning of polymer as a whole)
 Regular solution theory considers the statistical thermodynamics of solute
and solvent, specifically, the interactions between the components and the
possible configurations that the solute and solvent molecules can be
arranged relative to each other.
 For polymers, there is another consideration - the conformational contribution
of the polymer molecule to the free energy of mixing.
 The conformation refers to the statistical “shapes” that are available to given
polymer molecules.
 This is important because many of the properties of polymers are related to
the size and shape of the polymers themselves.
1-Mar-23

40. End-to-end Distance
 In flexible polymer molecular chains, each link is joined
randomly, and if one could start at the beginning of the chain
and trace a path along the chain, the final distance between
the two chain ends would be less than the end-to-end distance
of a stretched chain.
 In fact, the end-to-end distance of perfectly random chain
would scale as the square root of the number of links in the
chain.
 This is a useful concept but, unfortunately, the end-to-end
distance of a polymer molecule is a difficult parameter to
measure.
 Moreover, theories that assume random-flight polymers
necessarily assume unperturbed polymer chains (polymeric
chain without interactions).
1-Mar-23

41.  The conditions for an unperturbed chain are that the polymer segment-segment
interactions are exactly equal to the polymer-solvent interactions. This is
defined as the “theta” (ϴ) condition.
 The theta condition hovers between solubility and insolubility.
 Increase in solvency causes expansion of the polymer hydrodynamic volume,
and decrease in solvency causes collapse and phase separation of the
polymer from solution.
 Therefore, the theta condition, which is the basis of many statistical
thermodynamic theories of polymer solutions, is essentially experimentally
inaccessible, since even slight fluctuations of temperature or pressure will
cause a departure from theta conditions.
 Consequently, theta condition polymer dimensions are computed by
extrapolation from experimental measurements.
1-Mar-23

42. Radius of Gyration
 The radius of gyration of a polymer molecule is
the average distance of every link from every
other link in the chain.
 This is equivalent to measuring the average
distance of every point on the chain from the
center of gravity of the whole chain.
 The radius of gyration is a measure of the
distribution of mass in the molecule, and this
parameter can be measured by light-scattering
techniques.
1-Mar-23

43. The Hydrodynamic Radius
 Due to the constraints of the molecular chain, the “links” of polymer chains
cannot usually pack tightly together.
 There is always some excluded volume within the chain.
 In a good solvent, the chain swells and imbibes many molecules of solvent.
 It is not unusual for a polymer molecule to swell a hundred-fold or more when
immersed in a good solvent.
 The hydrodynamic radius is the radius of the equivalent sphere of a polymer
chain plus the solvent contained within that chain in solution.
 The hydrodynamic radii of polymer chains can be measured by viscosity,
dynamic light scattering, and size exclusion chromatography.
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44. Polymer Dimensions
 For real polymer chains, the chain is stiffened by, for example,
(1) bulky groups that hindered rotation around chain backbone
bonds,
(2) the formation of ring structures along the backbone,
(3) the formation of helical conformations,
(4) intermolecular crystallization between chains,
(5) interaction with a good solvent, or
(6) the presence of dissociated ionic groups in the polymer
molecule.
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45.  The stiffness of polymer molecules is characterized by their persistence
lengths or by their “Kuhn” lengths.
 The Kuhn length (the length of hypothetical segments that the chain can be
considered as freely joined) is twice the persistence length.
 Below the persistence length, the polymer molecule is “stiff.”
 Beyond the Kuhn length, a polymer molecule becomes flexible.
 The persistence length can be measured by dielectric relaxation, viscoelastic
relaxation, and ultrasonic relaxation techniques and by light scattering.
 The Kuhn length of stiff molecules like cellulose ethers is much longer than
that for acrylic polymers.
 Although the cellulose ethers are stiff and their thickening properties derive
from that stiffness, their molecule still become coils when they are longer than
the Kuhn length.
1-Mar-23

46. Basics of Dispersions
 A dispersion consists of a finely divided particulate
material suspended in an immiscible liquid.
 Emulsions are a special case of dispersions in which
the dispersed phase is also a liquid.
 Dispersions and emulsions are not
thermodynamically stable.
 They are pseudo stable, and the expectation for
cosmetic products is that the discontinuous
particulate phase can be maintained in stable
suspension for several years.
 Dispersion of finely divided solids in liquids cannot
usually be achieved by mechanical mixing alone.
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47.  The liquid must first thermodynamically wet the surface and interstices to
penetrate the interparticle interstices and cause disintegration of the dry
powder aggregates into their fundamental particles that are then uniformly
distributed throughout the liquid by mechanical mixing
 When a liquid spreads spontaneously on a solid surface, the solid-air
interface is replaced by a liquid-air interface and a liquid-solid interface.
 Each of these interfaces has surface energies associated with them.
 Spontaneous creation of new surfaces requires that the total free energy of
the surface(s) that are created should be less than the total free energy of the
initial surfaces.
 This means that the work of spreading has to be negative for spontaneous
spreading of a liquid on a solid surface.
1-Mar-23

48.  In order to break up an aggregate, the liquid must do more than just spread;
it must be forced into the pores of the aggregate.
 Therefore spontaneous penetration is favored by low solid-liquid interfacial
tension and high liquid-vapor tension, and small pore radius.
 Most surfactants lower both surface tension and interfacial tension.
 Therefore, disaggregation depends on the use of specifically adsorbing
surfactants that preferentially wet the solid-liquid interface rather than
adsorb at the liquid-air interface.
 Since surfactants adsorb at all interfaces, specific adsorption at the solid-
liquid interface ideally requires the choice of surfactants that adsorb by
dipole-dipole interaction, Lewis acid-Lewis base interaction, or opposite
charge attraction.
 The chosen surfactant should also be used sparingly to ensure adsorption
at the desired interface only.
1-Mar-23