Practical Mndern Hair Science
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`UNILEVER EXHIBIT 1055
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`IPR2013-00509
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`

`

`Practical Modern Hair Science
`www.Alluredbooks.com
`CHAPTER 3
`
`Shampoo and
`Conditioner Science
`
`Robert Y. Lochhead
`University of Southern Mississippi
`
`Shampoos and conditioners are the highest volume of products
`sold in personal care. In this chapter, we will consider the science
`that underpins the functioning of these product types. The principal
`function of shampoos is to cleanse the hair. However, since the
`introduction of two-in-one shampoos in the 1970s, it has not
`been sufficient for a shampoo to merely cleanse the hair. Modern
`shampoos should at least cleanse, condition, make the hair easier
`to style, and fragrance the hair with a pleasant, lingering smell.
`Modern conditioners should lower the friction between hair fibers to
`allow easier grooming and alignment of the hair fibers while leaving
`them glossy and avoiding lankness.
`The science of shampoos and conditioners is still evolving and
`in addition to describing fundamentals, this chapter attempts
`to take the reader to the frontiers of research in shampoo and
`conditioner science.
`
`Introduction
`Located within the hair follicle is a sebaceous gland that
`continuously excretes an oily material, known as sebum, onto
`the hair and scalp. This substance consists of compounds such as
`fatty acids, hydrocarbons, and triglycerides, and serves as nature’s
`conditioning treatment—providing lubrication and surface
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`hydrophobicity, while potentially replenishing components of
`the cell membrane complex. However, after a day or so, buildup
`of this substance begins to result in a greasy look and feel.
`Moreover, particulate dust and dirt adhere readily to this sebum
`layer. In modern cultures such sebum-soiled hair is deemed to
`be undesirable, and therefore, it should be removed on a regular
`basis by a facile process. This process is, of course, shampooing.
`Sebum cannot be removed by water because oil and water do not
`mix. Aqueous shampoos can remove oily soil from the hair surface
`because shampoos contain surface-active agents, commonly
`abbreviated as surfactants. The molecules of these surface-active
`agents self-assemble into micelles, which are the agents that
`solubilize oily soils.
`To understand how surfactants work, it is necessary to consider
`the exact process that leads to oil and water being incompatible.
`There are two different possibilities for substances to be insoluble
`in water. In one case, substances have stronger intermolecular
`cohesion than water. This is why substances like sand, clay, and
`glass are insoluble in water; the molecules of sand attract each
`other more strongly than the molecules of water and this attraction
`leads to the sand being insoluble. This reason for the insolubility is
`exactly opposite to the reasons for the insolubility of hydrophobic
`substances such as oils. The intermolecular forces between the oil
`molecules are weaker than the intermolecular bonds between water
`molecules and the oils are expelled from water. This expulsion arises
`largely from entropy and the effect has been coined hydrophobic
`interaction.1,2 From the time of the Phoenicians, it has been known
`that oil spreads to calm troubled waters. This effect arises from the
`fact that the spread oil has a lower surface tension than the water. At
`this point it is appropriate to consider the effect known as surface
`tension. Molecules in the bulk of liquids are attracted on all sides
`by their neighboring molecules. However, molecules at the surface
`are subjected to imbalanced forces because they are attracted by the
`underlying liquid molecules, but there is essentially no interaction
`with the vapor/gas molecules on the other side of the liquid/vapor
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`boundary. This imbalance leads to a two-dimensional force at the
`surface, namely surface tension. The surface tension is numerically
`equal to the surface free energy.3 The magnitude of surface tension
`directly correlates with the strength of the intermolecular forces.
`Water has hydrogen bonds, dipole-dipole interaction, and dispersion
`forces between its molecules, and as a consequence the surface
`tension of water is rather high—72 mN/meter at room temperature.
`On the other hand, only dispersion forces are present between the
`molecules of alkanes. As a consequence, the surface tension of
`alkanes is relatively low—ranging 20–30 mN/meter.
`Surfactants comprise molecules that contain two parts: a
`hydrophobic segment that is expelled by water and a hydrophilic
`segment that interacts strongly with water. Such molecules are said
`to be amphipathic (amphi meaning “dual” and pathic from the
`same root as pathos which can be interpreted as “suffering”). Thus,
`a surfactant molecule “suffers” both oil and water. This dual nature
`confers interesting properties on surfactants in aqueous solution.
`At very low concentrations, the surfactant is expelled to the surface,
`a process called adsorption. This adsorption causes the surfactant
`concentration at the surface to be much higher than the surfactant
`concentration in the bulk of the solution. At extremely low
`concentrations, when the surfactant molecules on the surface are
`located too far apart to effectively interact with each other, Traube’s
`Rule applies. Traube’s Rule states that the ratio of the surface
`concentration to the bulk concentration increases threefold for each
`CH2 group of an alkyl chain.4 This ratio is called the surface excess
`concentration.5 According to this rule, soap with a dodecyl chain
`should have a surface excess concentration that is more than a half-
`million times its concentration in the bulk solution. At extremely
`low concentrations, the surfactant molecules on the surface act as a
`two-dimensional gas. As the concentration increases, the surfactant
`molecules begin to interact, but they are still mobile within the
`plane; they behave as two-dimensional liquids. At even higher
`concentrations, as the surfactant saturates the surface, the chains
`orient out of the surface plane and the chain-chain interactions
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`cause the surfactant to behave as a two-dimensional solid. Irving
`Langmuir was awarded the 1932 Nobel Prize in Chemistry for
`measuring this effect and explaining it on a molecular basis.6
`When a surfactant adsorbs to saturate an aqueous surface, the
`surface is largely composed of the surfactant’s hydrophobic groups;
`this means that the surface essentially has low surface energy. As a
`consequence of the low surface energy, the surface area is easier to
`expand to a film. This means that the system is easier to foam, since
`aqueous foams really consist of water films with entrapped gas. If
`the foam surface is structured by the adsorbed surfactant, then foam
`stability can be achieved.7
`
`Surfactant Micelles
`Relatively large aggregates form within solution just beyond
`the concentration at which the surface becomes saturated with
`surfactant.8 These aggregates are surfactant micelles in which
`the hydrophobes are segregated within the core of the aggregate
`and the hydrophilic groups are located on the surface where they
`interact strongly with water.9 For a given system, micelles initially
`form at the precise concentration at which the driving force for
`surface adsorption becomes equal to the driving force for aggregate
`formation. This driving force is the chemical potential of the
`surfactant species. The lowest concentration at which micelles form
`is named the critical micelle concentration (CMC). The aggregates are
`large; for example, micelles of sodium dodecyl sulfate at the CMC
`contain about 100 molecules and the thickness of the head group
`layer is about 0.4 nm.10
`Surfactant micelles have liquid centers. They effectively solubilize
`hydrophobic substances only when the temperature of the system is
`above the Krafft point. Krafft found this phenomenon in 1895, and
`68 years later Shinoda explained that the Krafft point corresponds to
`the melting point of the hydrated solid surfactant.11
`Micelles have different shapes. The simplest shape is the
`spherical micelle that was postulated by Hartley in 1936. The
`shape of a micelle can be explained on the basis of the principle
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`of opposing forces (see Figure 1). Two or three amphipathic
`molecules alone cannot form a stable micelle because micellization
`is essentially a cooperative process that requires the participation
`of many amphipathic molecules bound together by hydrophobic
`interaction. However, if hydrophobic interaction accounted solely
`for the formation of micelles, then the association would continue
`until phase separation occurred, as in oil separating from water.
`Therefore, there must be a force that opposes the hydrophobic
`association and controls the size of the micelles. This force is the
`repulsion between the head groups that could arise from ion-ion
`repulsion and/or hydration of the head groups.12 Theoretically,
`the repulsive surface terms are difficult to handle from a
`thermodynamic perspective but the presence of micelles has been
`validated experimentally.
`
`Figure 1. The shape of a surfactant micelle is determined by
`the balance between the mutual repulsion between hydrophilic
`groups at the micelle surface and the cohesion due to hydrophobic
`interaction. This has been dubbed the principle of opposing forces.
`
`If micelle structure was determined solely by thermodynamics,
`spherical micelles would always be favored over other shapes.
`However, real micelles are not restricted to a spherical shape;
`spherical structures account for only a small minority of micelles.
`The shapes of surfactant molecules and the way they can be packed
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`also plays an important role in determining micelle shape. Although
`thermodynamics and packing geometries are inextricably linked,
`by considering the limits of possible packing arrangements we can
`obtain insight into the shapes of micelles and the transformation
`from one shape to another as physical and chemical conditions
`are changed. In this context, the many shapes of micelles, arising
`from the principle of opposing forces, can be appreciated by
`considering Packing Factor Theory (Figure 2).13 First, consider a
`spherical micelle. In this instance the micelle radius, R, the volume
`of the hydrophobic core, v, and the surface area of the amphipathic
`molecule at the hydrophobe/water interface, a, are related by:
`
`
`
`
`
`
`
`Eq. 1
`
`
`
`
`
`The radius of a micelle, R, cannot exceed the fully extended
`length, l, of the hydrophobe chain of the surfactant molecule. This
`gives the critical condition for the formation of spherical micelles:
`
`
`
`
`
`
`
`
`
`
`
`
`
` Eq. 2
`
`Figure 2. The packing factor of a surfactant molecule is the volume of
`the tail group divided by the volume of the cylinder subtended by the
`head group to the length of the tail group.
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`The fraction, v/al, is known as the packing factor (Figure 3).
`When the packing factor has a value of 1/3, the surfactant molecule
`can be approximated by a conical shape and the molecules pack into
`a sphere (Figure 4).
`
`Figure 3. Surfactant molecules with a packing factor of 1/3 have a
`shape that can be approximated by a cone.
`
`Figure 4. These conical molecules pack naturally into a sphere.
`
`When the packing factor has a value of ½, the micelles become
`cylinders (Figure 5), and when the packing factor has a value of
`1, the surfactant molecules pack as planar bilayers in a so-called
`lamellar structure (Figure 6).
`For ionic surfactants, the area per head group can be decreased
`by adding soluble salt to the solution to lessen the ionic repulsion
`between the head groups. (Salt also enhances the hydrophobic
`interaction.14) Increase in salt and/or surfactant concentration causes
`spherical micelles to transition to rods and then to long worm-like
`micelles.15 The wormlike micelles behave like polymers in solution.16
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`These micelles also form branched as well as linear structures, and
`above a certain concentration (the critical overlap concentration, C*)
`they entangle just like polymer molecules17 and display viscoelastic
`rheology.18-20 This behavior is depicted in Figure 7 as it was
`explained by Candau in 1993.21 An increase in salt concentration
`causes spherical or elliptical micelles to transition into rods, then
`to worms then to branched worms. As the surfactant concentration
`increases, the micelles form entangled networks. Consumers desire
`
`Figure 5. Surfactant molecules with a packing factor
`of ½ pack naturally into cylinders.
`
`Figure 6. Surfactant molecules with a packing factor of 1 pack
`naturally into bilayer planes.
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`Chapter 3
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`thicker shampoos, in part because they are easier to apply, but
`also for aesthetic reasons; a thicker formula is generally perceived
`as being more-luxurious. The desired rheology is achieved from
`formulations that contain worm-like micelles.
`
`Figure 7. Ionic surfactant micelles change shape as a function of ionic
`strength and surfactant concentration.
`Wormlike micelles do, however, show “non-polymeric” behavior
`at certain shear rates when the shear stress becomes independent of
`the shear rate and the relaxation time becomes monodisperse.22 This
`behavior has been explained on the basis that the entanglements
`can be broken and reformed as the rod-like micelles disassemble
`and then reassemble upon passing through each other.23-24 Systems
`like these have been dubbed “phantom networks” by Cates to
`signify that one micelle flows through another just as we imagine a
`phantom would pass through a wall. The phantom network behavior
`may explain why shampoos can show viscoelasticity without the
`“stringiness” observed in entangled polymer solutions.
`At higher concentrations, the rod-like micelles mutually repel,
`and this favors alignment into a nematic phase. At still higher
`concentrations the aligned rods pack in a hexagonal array to form
`hexagonal phase liquid crystals (Figure 8). The hexagonal phase
`has the properties of a clear ringing gel that is birefringent in
`polarized light.
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`Figure 8. Rod-like micelles can pack into hexagonal liquid crystal phase.
`As the surfactant concentration is increased further and/or
`dissolved salt concentration is increased, the surface of the micelles
`becomes less curved until the large planar aggregates of the lamellar
`phase are formed (Figure 9). Modern shampoos consist essentially
`of entangled worm-like micelles and conditioners are usually in the
`form of the lamellar phase.
`
`Figure 9. Increase in surfactant concentration causes micelles to transition from
`spheres to rods to hexagonal phase to lamellar phase to inverse hexagonal
`phase to inverse micelles.
`
`In summary, shampoo and conditioner formulation essentially
`involves the preparation of surfactant mixtures that possess the
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`aforementioned structures, while also being esthetically pleasing.
`The hair care formulation scientist has an ever-increasing variety
`of surfactants available in the formulation toolbox, and so these
`structures can be obtained via a wide range of concoctions.
`Nonetheless, attaining such stable structures is not a trivial task,
`due to the presence and interactions of so many ingredients in
`the typical formulation. Therefore, with historical knowledge
`involving many established ingredients already being relatively
`well-understood, it is a brave formulation chemist that opts to cut a
`new pathway. Moreover, it is also probably prudent to arrive at these
`structures in the most cost-effective manner. For these reasons, it
`is imperative to understand how the surfactant structure, together
`with interactions with other molecules alters the nature of the
`aggregate structures.
`
`Oily Soil Removal Mechanisms
`The principal function of a shampoo is to remove oily soil from
`the hair. There are several principal detergency mechanisms for
`removing oily soils: “roll-up,”25 emulsification, penetration, and
`solubilization.
`In the roll-up mechanism, the detergent solution causes a steady
`increase in the contact angle of the oil at the oil/fiber/aqueous
`interface (Figure 10).
`
`Figure 10. In this mechanism the oil contact angle at the oil/water/fiber interface
`steadily increases until it “rolls up” and floats off of the solid surface. This
`mechanism was first reported by N. K. Adams.
`
`The oil droplet is rolled up on the surface, and when the contact
`angle reaches 180 degrees, the interfacial force that is holding it to
`the surface is overcome by the wetting tension of the oil and aqueous
`solutions on the fiber surface. Roll-up is favored by fibers that are
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`oleophobic and hydrophilic.26 The removal of oily soil by detergent
`compositions is not necessarily predictable due to the wide variation
`of the surface properties of hair that arise from prior treatments
`and weathering. Moreover, the transport of the detergent solution
`to the fiber surface can occur by three different routes: (i) along the
`fiber surface, (ii) through a previously applied permeable surface
`treatment, or (iii) through the body of the fibers (Figure 11).
`
`Figure 11. In the roll-up mechanism, the detergent solution can be transported
`to the fiber/oil interface along the fiber surface, through a permeable coating
`on the fiber, or through the fiber itself.
`
`Roll-up of oily drops on fibers occurs when the contact angle
`exceeds a critical value and this causes the oily drop to adopt an
`unstable axially asymmetric attachment on one side of the fiber.27
`The rate of roll up depends also on the viscosity of the oily soil,
`and mechanical action is often necessary to dislodge viscous oily
`soils from the fiber surface. In some cases, the oil forms a viscous
`emulsion when contacted by the detergent composition, and the
`resulting viscous soil can be difficult to remove from the fiber.
`“Perfect” hair is covered by a covalently attached monolayer of
`18-methyleicanosoic acid (18-MEA), which confers hydrophobicity
`on the hair. Modern grooming techniques and weathering removes
`this layer of 18-MEA.28 Removal of the layer of 18-MEA results
`in hair becoming macroscopically hydrophilic.29 The roll-up
`mechanism, therefore, should be expected to become more
`prominent on damaged rather than pristine hair.
`Initially if the fiber is completely coated in oil, or if the fiber itself
`is hydrophobic, the detersive solution cannot easily reach the oil/fiber
`interface, and the soil will be removed by emulsification (Figure 12).
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`Emulsification is favored by low oil/water interfacial tension that
`allows the oil surface to be expanded into an emulsion droplet.30
`
`Figure 12. Emulsification can remove the soil if the interfacial tension between the
`oily soil and the surfactant solution is low.
`
`In the penetration mechanism of oily soil removal, surfactant-
`rich phases penetrate the oil at the interface. This results in an
`interfacial liquid crystalline phase that swells and is broken off
`to reveal a fresh soil interface, and then the process is repeated
`again and again.31 The penetration mechanism occurs with polar
`soils and/or phase separated coacervates of nonionic surfactants
`above the lower critical solution temperature (LCST). Spontaneous
`emulsification, in the absence of detersive surfactant, has been
`observed for non-polar-polar soil mixtures like sebum.32 The
`penetration mechanism can occur with anionic surfactants that
`form coacervate phases in the presence of calcium salts.33
`Solubilization is the process of incorporating a water-insoluble
`hydrophobic substance in the internal hydrophobic core of micelles.
`Direct solubilization can occur in the presence of an excess of
`surfactant micelles with respect to oily soil.34 The rate of exchange
`of surfactant molecules between micelles is important because the
`micelles must re-assemble around the soil to solubilize the soil by
`encompassing it inside the micelle.
`
`Foam/Lather
`One essential attribute of a shampoo is its ability to produce
`a rich lather or foam. The important elements of a foam are
`the lamellae and the Plateau border. The micrograph in Figure
`13 depicts these structural features of a foam. The lamellae are
`stabilized by surfactants adsorbed at the air-water interface.
`
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`Figure 13. Micrograph showing surfactant foam structure.
`
`Foams lose stability by two main mechanisms: draining of the
`liquid and puncture of the lamellae. The foam lamellae are the
`junctions between two foam bubble cells and the plateau border is
`situated at the triple-cell junction. The Laplace pressure in the liquid
`components of the foam is inversely proportional to the curvature
`of the interface. The higher curvature of the plateau border results
`in a lower pressure in that region and this causes the liquid in the
`foam to drain preferentially from the lamellae to the plateau borders.
`Based upon this reasoning, it can be understood that drainage can
`be hindered in two ways, namely by blockage of the lamellae or by
`blockage at the plateau border. About two decades ago, Des Goddard
`carefully measured the drainage from foam films and deduced
`that polyquaternium-24 adsorbed across the lamellar interface and
`hindered the drainage of liquid from the foam. In addition, about
`thirty years ago, Stig Friberg concluded that certain liquid crystals
`blocked the plateau border region and delayed foam drainage and
`conferred longer-term stability on surfactant foams. In the case of
`cationic polymers, hindered drainage of the lamellar liquid could be
`caused by adsorption of the cationic entities at the lamellar surface
`with the nonionic and/or anionic blocks in the lamellar liquid.
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`Alternatively, formation of phase-separated coacervates between the
`cationic polymer and the anionic surfactant could result in blockage
`of the plateau border. Of course, if the interaction of the cationic
`polymer was strong enough to form “inverse micellar” structures,
`then there would be a possibility that the phase-separated particles
`could cause a local reversal of the curvature in the lamellae and this
`in turn would result in breakage of the lamellar film and subsequent
`foam destabilization. This type of foam destabilization mechanism
`has been extensively reported by Peter Garrett.
`
`Solid Foams
`Cationic conditioners
`that would normally be
`incompatible with liquid
`shampoos can be delivered
`from solid foams. Solid
`foams also make it possible
`to have one scent for the
`solid and then to allow
`a different fragrance to
`bloom when the solid is
`wetted by water.35 The
`porous solids are made by
`mixing the surfactants,
`glycerin as a plasticizer,
`and water in the presence
`of a water-soluble polymer.
`Figure 14 shows a solid
`foam in which poly(vinyl
`alcohol) is the water-soluble
`polymer. After a heating
`and mixing cycle, the
`porous solid is formed by
`aeration.
`
`Figure 14. Micrograph showing solid foam structure
`(reproduced from US Patent Application 20110195098).
`
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`The Anatomy of a Shampoo Formulation
`Shampoos consist essentially of water, a primary surfactant,
`one or more co-surfactants, and soluble salt. Other ingredients
`are added for fragrance, preservation, conditioning, and styling
`attributes. Cleaning is achieved mainly by the primary surfactant,
`which is often an anionic surfactant that would adopt a conical
`shape if it was present in water alone. The co-surfactant is usually
`a nonionic or zwitterionic surfactant with a relatively small head
`group surface area. This molecular shape allows the co-surfactant
`to serve two roles: (i) it packs between the molecules of the primary
`surfactant to reduce the curvature and to promote the formation
`of worm-like micelles with their high viscosity and luxurious
`rheology; and (ii) it packs between the primary surfactant in the
`lamellae of the foam to provide good lather that is easily removed
`by rinsing. Salt enhances the function of the co-surfactant by
`“damping down” the ionic repulsion between primary surfactant
`head groups and promoting the formation of wormlike micelles. If
`excess salt or co-surfactant is added, shampoo compositions can
`separate into phases that contain co-existing micelles and liquid
`crystals. These phase-separated compositions often exhibit thin
`viscosities and haziness.
`
`The Primary Surfactant
`The lauryl sulfates have been the primary surfactant workhorses
`of the shampoo industry for decades. The sulfate head groups bear
`an anionic charge when dissolved in water. The long chain alkyl
`tail group has an average length of 12 carbon atoms. It is important
`to understand that this is an average chain length; commercial
`lauryl sulfates have a distribution of chain length from as short as
`8 carbons to as long as 18 carbons. This chain length distribution
`changes from supplier to supplier and it also changes depending
`on the source of raw materials. Formulators should be aware that
`changes in the chain length distribution of the surfactants can lead
`to subtle changes in the properties of the shampoo.
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`During the 1970s, triethanolamine lauryl sulfate was preferred
`as a primary surfactant due to its excellent cleaning properties and
`luxurious flash foaming capability. However, it was replaced by
`laureth sulfates for two reasons: the concern over the formation of
`nitrosamines from secondary amine components and the reduced
`eye irritation exhibited by the laureth sulfates.
`Over the last two decades, the primary surfactants of most
`shampoos have been sodium laureth sulfate, ammonium lauryl
`sulfate, and sodium lauryl sulfate.
`The co-surfactant–often called the foam booster–has most
`prominently been selected from two types of materials: alkylamide
`MEA and alkylamidobetaines. Modern shampoos contain primarily
`betaines as co-surfactants.
`
`Enhancing Mildness
`Isethionates are surfactants noted for their mildness to skin,
`and for at least three decades, they have been the basis of non-soap
`detergent bars such as Dove (Unilever). They have been making
`inroads into shampoos based upon mildness claims. Moreover,
`Unilever researchers discovered that the mildness can be enhanced
`even further by including mildness benefit agents that can be
`flocculated by cationic polymers present in the formulation and
`delivered as flocs upon dilution of the formulation.36 The preferred
`benefit agent in this case is petrolatum; the cationic polymers
`are well known polymers like polyquaternium-10 and guar
`hydroxypropyltrimonium chloride. This could form the basis of
`shampoos that are mild to the skin.
`Certain non-cross-linked linear acrylic copolymers can lower
`the irritation potential of surfactants and provide products that are
`clear and highly foaming.37 The preferred polymers interact with the
`surfactant and effectively shifting the CMC to higher concentrations,
`while lowering the critical aggregation concentration—the latter
`being the concentration at which the surfactant selectively interacts
`with the polymer rather than adsorbing at the liquid surface
`(Figure 15). It is postulated that free surfactant molecules and
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`Shampoo and Conditioner Science
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`free surfactant micelles are responsible for irritation of skin and
`eyes and that binding of the surfactant to the polymer effectively
`reduces the concentration of free micelles. A measure of mildness
`is the delta CMC, which is defined as the difference between the
`CMC of the surfactant alone and the higher CMC of the surfactant
`in the presence of the polymer. Larger values of delta CMC for a
`particular surfactant are apparently correlated with lowering of the
`irritation potential. The delta CMC provides a measure that is useful
`for selecting, comparing, and optimizing polymers that reduce the
`irritation potential of selected surfactant systems. Carbomer and
`acrylates copolymer have been identified as polymers that exhibit a
`satisfactory delta CMC.
`
`Figure 15. Plot of surface tension vs. surfactant concentration for
`surfactant alone and for surfactant in the presence of polymer. The
`difference in the CMC induced by the presence of the polymer is
`claimed to be related to the effect of the polymer in enhancing the
`mildness of a shampoo.
`
`Conditioning Shampoos
`Today’s conditioning shampoos are expected to confer wet-hair
`attributes of hair softness and ease of wet-combing, and the dry hair
`attributes of good cleansing efficacy, long-lasting moisturized feel,
`and manageability with no greasy feel.
`The origin of conditioning shampoos can be traced to the
`balsam shampoos of the 1960s followed by the introduction of
`polyquaternium-10 by Des Goddard38,39 in the 1970s and 1980s in
`which he introduced the concept of polymer-surfactant complex
`coacervates that phase-separate and deposit on the hair during
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`Chapter 3
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`rinsing. The first two-in-one shampoos depended on a complex
`coacervate being formed between anionic surfactant and the
`cationic hydroxyethylcellulose, polyquaternium-10. This complex
`was solubilized in excess surfactant and it phase-separated as a
`coacervate liquid phase upon dilution during the rinsing cycle.
`Later guarhydroxypropyltrimonium chloride was introduced as
`an alternative cationic polymer that worked on the same principle
`as polyquaternium-10. These two polymer types continue to
`dominate the compositions of conditioning shampoos.40 Guar is a
`galactomannan and it is interesting that, in recent years, recently
`a new cationic galactomannan hydrocolloid, cationic cassia,
`has been claimed to confer conditioning shampoo benefits.41,42
`Polygalactomannans consist of a polymannan backbone with
`galactose side groups. In guar gum, there is a pendant galactose
`side group for every two mannan backbone units. These galactose
`groups sterically hinder the substitutable C-6 hydroxyl unit,
`limiting the extent of possible cationic substitution on guar gum.
`In cassia, however, there is less steric hindrance of the C-6 hydroxyl
`group and, consequently, higher degrees of cationic substitution
`are possible with cassia (60% for cassia relative to 30% for guar).
`Cationic cassia can be used as a conditioning polymer in shampoos
`and conditioners to impart cleansing, wet-detangling, dry-
`detangling, and manageability.
`The mechanism of conditioning shampoos depends upon the
`formation of polymer/surfactant coacervates that phase-separate
`during