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Shampoo and Conditioner ScienceRobert Y. LochheadUniversity 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.

IntroductionLocated 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 MicellesRelatively 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.

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

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.


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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).

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

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.


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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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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.

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.

Figure 7. Ionic surfactant micelles change shape as a function of ionic strength and surfactant concentration.


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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.

In summary, shampoo and conditioner formulation essentially involves the preparation of surfactant mixtures that possess the

Figure 8. Rod-like micelles can pack into hexagonal liquid crystal 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.

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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 MechanismsThe 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).

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

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.


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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).

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).

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.

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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

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/LatherOne 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.

Figure 12. Emulsification can remove the soil if the interfacial tension between the oily soil and the surfactant solution is low.


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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.

Figure 13. Micrograph showing surfactant foam structure.

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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 FoamsCationic 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 FormulationShampoos 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 SurfactantThe 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 MildnessIsethionates 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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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.

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

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.

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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 rinsing (Figure 16). Polyions in aqueous solution are surrounded by an electrical double-layer of counterions, and the location of the counterions with respect to the polyion is determined by a balance between chemical potential and electrochemical potential, called the Donnan Equilibrium. Surfactant ions contain a large hydrophobic group that makes them intrinsically less soluble in water than inorganic ions such as chloride or bromide. When surfactant ions interact with an oppositely charged polyion, they bind strongly and displace the water-soluble inorganic ions from the polyion; that is, they ion-exchange. Once the surfactant ions


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bind, hydrophobic interaction between the hydrophobic surfactant tails causes the polymer-surfactant complex to phase separate at concentrations below the surfactant critical micelle concentration.

Above the CMC, the surfactant concentration is sufficiently high to form micelles or hemi-micelles along the polyion chain, and the polyion/surfactant complex is solubilized. Conditioning shampoos are formulated within the range of surfactant concentrations that correspond to this solubilized regime. When these shampoos are diluted to a concentration that is in the vicinity of the CMC, then the complex coacervate phase-separates. The separated phase is deposited on the hair during rinsing, and it can co-deposit other additives such as silicone conditioning agents or anti-dandruff agents. Maximum coacervate deposition occurs at precise ratios of cationic polymer to anionic surfactant, but the optimum ratio for coacervation might not coincide with the best ratios for cleaning and foaming.

Cationic guar has been a known additive for 2-in-1 shampoos for more than three decades. However, it has now been shown that improved post-shampoo detangling times are achieved by including a small degree of hydrophobic substitution in the cationic guar derivatives.43

Figure 16. A schematic phase diagram that explains the mechanism of coacervate formation in 2-in-1 shampoos.

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Synthetic copolymers of acrylamide and a Triquat monomer are postulated to provide improved deposition on hair and improved conditioning performance with respect to wet combing.44

Silicones have become standard ingredients in many conditioning shampoos for the smooth, silky hair feel that they confer. Silicones were introduced to shampoos as 2-in-1 conditioning agents in the 1980s. The introduction of silicones needed to overcome two substantial deficiencies: (i) silicones are well known defoamers, and (ii) silicones are incompatible with typical shampoo compositions and they tend to separate due to their low specific gravity. Initial attempts to stably suspend the silicone included the use of water–miscible saccharides such as corn syrup.45 Later products comprised xanthan gum in the shampoo as a suspending agent and acceptable foaming attributes were conferred on the shampoos by formulating with relatively high levels of alkyl sulfates as the primary surfactant, cocamide MEA as the co-surfactant, and ethylene glycol distearate as a surfactant structuring agent.46 In the actual application, there is a technical contradiction involved in the deposition of silicone conditioning components from a detersive, cleansing system; the detersive system is designed to remove oil, grease, dirt, and particulate material from the hair, and the conditioning agent has to be deposited on that same hair in one process. As a result, large excess amounts of silicone are used to ensure deposition, and one consequence of this is that large amounts of the expensive conditioning silicone can be rinsed away rather than deposited on the hair. Cationic polymer/anionic surfactant coacervates enhance the deposition of silicones on hair and, consequently, increase the efficiency of conditioning shampoos.47,48

Volatile cyclic siloxanes confer the desired silky initial feel, but these materials are difficult to formulate in consistent homogenous formulations, They tend to spread uncontrollably over the hair and skin.49 This effect can be controlled with polymeric silicone gels formed in volatile silicones to provide both the initial silky feel and a high viscosity and smooth feel when dry.50 Branched molecules with a silicone core and hydrocarbon branches, or networks formed from


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these branched units, have been disclosed as suitable for improving sensory feel, while minimizing phase separation and conferring good shampoo removability.51

Shampoos containing more than one cationic conditioning polymer and a quaternary silicone give more uniform deposition on hair than standard shampoos based on polyquaternium-10 as the sole conditioning polymer. Thus, a conditioning polymer “cocktail” comprising poly(acrylamide-co-acrylamidopropyltrimonium) chloride, guar hydroxypropyltrimonium chloride, and silicone quaternium-13 give uniform deposition on hair. In this instance, the claims are based upon multiple testing and analysis:52

•Amultipleattributeconsumerassessmentstudythatmeasuredthe attributes of cleanliness, wet-comb, dry-comb, hair softness, lather amount, and creaminess.

• SecondaryIonMassspectrometrytodetectsilicononthehairsurface. This method revealed that a standard commercial shampoo concentrated silicone on the cuticle edges of the hair, whereas the patent application shampoo “distributed silicone more evenly.”

•X-rayphotoelectronspectroscopy(XPS)tomeasurethethicknessof the silicone polymer layer on hair from Si:C:O ratios. This method revealed that the commercial shampoo deposited a significant amount of silicone, and the patent application shampoo deposited only one or two molecular layers.

• Instronringcompressionasameasureofcombability.

Complex coacervates can also be formed from mixtures of cationic and anionic polymers. This could be the underlying mechanism in shampoos that include an anionic and cationic polymer that provide sleekness and gloss.53

Two drawbacks of silicones are that they often destabilize foam and the final compositions are hazy due to light scattered from the suspended silicone droplets. Initially, silicone copolyols were introduced to overcome the insolubility of silicones in shampoo compositions, but this drastically reduced the amount of silicone

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deposited onto hair and compromised conditioning performance. Clear, silicone-containing conditioning shampoos have been formulated by adding trideceth-2 carboxamide MEA to reduce the silicone droplet size.54 Transparent conditioning shampoos can be formulated by incorporating the silicone as microemulsified droplets, but the small microemulsion droplets tend to be rinsed away rather than deposited during the shampooing process. Moreover, coalescence of the droplets can lead to loss of transparency in the product during storage. Attempts have been made to overcome these challenges by including silicone emulsions with high internal viscosities, typically greater than 100,000 centistokes, but the high internal phase viscosity gives deposited silicone that is can be difficult to remove and this causes buildup with each consecutive shampooing. Such buildup usually reduces the volume of the desired hair style and causes “droop” and flatness. Fortunately, shampoo compositions providing superior conditioning to hair while also providing excellent storage stability and optionally high optical transparency or translucency can be obtained by combining low viscosity microemulsified silicone oil with cationic cellulose polymers and cationic guar polymers having molecular weights of at least about 800,000 and charge densities of at least about 0.1 meq/g.55 Conditioning shampoo formulations that include a silicone microemulsion in a conditioning shampoo containing guar hydroxypropyltrimonium chloride and an anionic detersive surfactant have also been reported to be clear.56,57 If pre-gelatinized starch, such as hydroxypropyl distarch phosphate, is included with polyquaternium-10, transparent conditioning shampoos can be obtained.58

Another way to minimize buildup is to treat the hair with water-in-water emulsions that can be prepared by including cationic polymers with soluble salts in surfactant compositions.59 These water-in-water emulsions provide conditioning benefits with good spread of the conditioning phase on the hair and less chance of buildup.

The living free radical polymerization techniques that have emerged in the last decade offer the prospect of preparing precise polymers with unprecedented accuracy in molecular structure and


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variety of chemical types.60 This technique has enabled synthesis of a wide diversity of block and graft polymers that were previously unattainable. Such polymers offer the prospect of conferring conflicting properties within one molecule, which in turn can lead to improved compatibilities in the same system while maintaining stability. These conflicting properties could possibly be achieved by blending different polymers, but different polymers do not mix readily at the molecular level and phase separation may result.61 Block, graft, and gradient copolymers serve to compatibilize such compositions and gradient polymers have been proposed for this purpose. Block copolymers comprising polycationic blocks and nonionic blocks for surface deposition62 and for improved foam retention63 have been claimed, which are desired to deposit on hair in order to modify the chemical properties of the surface for protection or compatibility; to modify hair’s hydrophobic or hydrophilic surface properties; or to modify feel or mechanical properties of the substrate from two-in-one products. The polymers disclosed are block copolymers of polyTMAEAMS (methylsulfate [2-(acryloyloxy)ethyl]-trimethylammonium) g/mole) and polyacrylamide.

Conditioning shampoos can also be formulated to function by mechanisms other than cationic polymer-induced complex coacervation, such as:

•Conditioningcanbeachievedbyincludingchainextendedsilicones in an anionic surfactant-based shampoo. Specific examples of useful silicones include silicone emulsions containing divinyldimethicone/dimethicone copolymer.64

• Shampooscontainingpolyalkyleneoxidealkyletherparticlesgive larger coacervate cohesive flocs (20–500 microns) that resist shear and confer superior deposition efficiency on hair for good wet conditioning.65

•Conditioningshampooscontainingapolyesterformedfromadipic acid and pentaerythritol provides conditioning for dry hair (possibly from reduced hair friction), with no greasy feel.66

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• Inclusionofpolybuteneisthoughttoincreasethedepositionof silicone conditioners and provide improved conditioning benefits, such as wet and dry feel and combing.

O’ Lenick disclosed a unique class of alkyl polyglucoside quaternary surfactants possessing all the multifunctional attributes of cleansing, conditioning, and self-preserving.67 This could have the potential of greatly simplifying the formulation of multifunctional shampoos.

A conditioning shampoo that contains a conditioning gel phase in the form of vesicles is described by Unilever researchers.68 Cationic conditioners are usually incompatible with anionic shampoos, and consequently conditioners based upon cationic surfactants are usually applied as separate post-shampoo products. The Unilever researchers prepared a conditioning gel phase by combining a small amount of water, fatty alcohol, a long-chain secondary anionic surfactant (sodium cetostearyl sulfate), and a long-chain cationic surfactant (behenyltrimethylammonium chloride), and subjecting the mixture to high shear to form a stable vesicular gel phase. Prolonged shear causes the lamellar gel phase to roll-up into an array of multilamellar vesicles (Figure 17). The gel phase was added to a dilute primary surfactant solution (sodium laureth sulfate) to form a conditioning shampoo that conferred good wet smoothness on hair.

Deposition of Particles on Hair to Confer Styling BenefitsWhereas conditioning shampoos are formulated to reduce hair

inter-fiber friction, some consumers need an increase in friction in

Figure 17. Lamellar gel subjected to high shear rolls up into vesicles of gel phase that can be used for conditioning. (Figure reproduced from US Patent Application 20110243870).


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order to achieve styling benefits. Factors that influence hair body and fullness include hair diameter, hair fiber-to-fiber interactions, natural configuration (kinky, straight, wavy), bending stiffness, hair density, and hair length. Increases in friction can be achieved by depositing particles such as titanium dioxide, clay, pearlescent mica, or silica on the hair surface. Particles can be deposited for more purposes than merely increasing inter-fiber friction, e.g., for conferring color, for slip (spherical particles are best for this), and for conditioning (hollow silica, hollow polymer particles). Hollow particles can be included in shampoo to increase hair volume.69,70 Deposited hollow particles that can increase fiber-fiber interaction include complexes of gas-encapsulated microspheres (such as silica modified ethylene/methacrylate copolymer microspheres and talc-modified ethylene/methacrylate copolymer microspheres); polyesters; and inorganic hollow particles.

It has already been noted that cationic guar enhances the deposition of conditioning agents. In a like manner, this macromolecule enhances the deposition of particles on hair.71 Silicones and particulates can be deposited simultaneously. Thus, enhanced deposition of particulate actives, such as zinc pyrithione (shown on cadaver skin treated in a Franz diffusion cell), has been reported72 from shampoos comprising a water-soluble silicone (such as silicone quaternium-13, cetyltriethylammonium dimethicone copolyol phthalate, or stearalkonium dimethicone copolyol phthalate), a cationic conditioning agent (such as acrylamidopropyltrimonium chloride/acrylamide copolymer, or guar hydroxypropyltrimonium chloride), a cleansing detergent, and suspending agents (such as carbomer, hydroxyethylcellulose, and PVM/MA decadiene cross-polymer) to insure homogeneous distribution of the insoluble active.

Hydrophobic modification of cationic hydroxyethylcellulose is claimed to endow better efficacy. Thus, polyquaternium-24, a hydrophobically modified cationic hydroxyethylcellulose, is also disclosed as being a preferable thickener for zinc-depositing compositions.73

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It has been discovered that responsive particles, with two contrasting polymers adsorbed to the particle core,74 can adsorb to the hydrophilic hair surface and render it hydrophobic, thereby conferring conditioning attributes to the hair. For example, grafting of aminopropyl-terminated dimethicone and polyethylenimine on titanium dioxide particles produces responsive particles. These particles form stable dispersions in water and aqueous solutions because they are sterically stabilized by expansion of the polyethylenimine into the aqueous medium. However, when they are deposited on hair and dried, the polyethylenimine layer collapses and the dimethicone layer expands to render the surface hydrophobic. The usefulness of these responsive particles is demonstrated by including them in typical conditioning shampoo and conditioner formulations. In the case of the shampoo, inclusion of the responsive particles results in a higher water contact angle on the treated hair and the conditioner with particles causes an increase in the hydrophobicity of the hair. On the other hand, shampoos containing ethoxylated alcohols have been found to enhance the deposition of large particle silicones (5–2000 microns), and in this case it is claimed that cationic polymer is not required.75

Two-phase Systems for Visual Attributes: There is esthetic appeal to products that exist as separate phases

in the bottle but which mix during application to provide added benefit, such as moisturizing or conditioning, by interaction of the components of the two phases. The most obvious way to formulate such products is to use the immiscibility of water and oil in formulations that are shaken prior to use to produce a metastable emulsion. However, when a surfactant is included in the system such a visually attractive phase separation can be mixed into an emulsion due to shear in manufacturing and packing operations. There are known de-emulsifiers, which are widely used in the oil industry, but these demulsifiers also tend be defoamers that compromise the lather of shampoos. Neutralized polyacrylate can be added as a non-emulsifying foam stabilizer to yield phase-separated compositions


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that resist the production difficulties to make phase-separated shampoos that form temporary emulsions upon shaking and foam during use.76 A two-phase shampoo system can also be formed by mixing polar lipophilic shampoo components with non-polar lotion constituents such as mineral oil.77

Under appropriate conditions, phase-separated systems can be prepared from polymer solutions or micellar surfactant solutions. If two distinct aqueous phases are desired in a composition, one must take into consideration the thermodynamics of coexisting phases and the driving force for such phase separation that comes directly from the chemical thermodynamics of the system. This is especially the case for systems that contain polymers or micelles because the configurational entropy is reduced as molecules are assembled into polymers or aggregated into micelles, and mixing can become unfavorable. If the free energy of mixing is insufficient to maintain uniform dispersion, spontaneous phase separation will occur. Phase separation becomes more likely as the micellar aggregates or polymers get bigger. The addition of salts to ionic surfactant micellar systems causes a reduction in the surfactant intra-micellar head-group interaction, and often an increase in hydrophobic interaction. This can cause a pronounced increase in micelle size and consequent phase separation into a surfactant-rich phase and a surfactant-poor phase. This approach has been adopted by adding mineral salt to induce two distinct layers,78 and by adding the detergent builder, sodium hexametaphosphate, to cause phase separation. In this case, a thickener is required and the system comprises a surfactant, a thickener, a polyalkylene glycol, and a non-chelating mineral salt. The system spontaneously separates into two layers.

A multiphase composition comprising surfactant, betaines, co-surfactant (such as an alkyl ether carboxylate, an acylglutamate; or an acylisethionate), and an appropriate concentration of salt forms a stable multiphase system that becomes temporarily uniformly dispensed upon agitation.79

Multiphase cleansing products have been introduced that go beyond mere phase separation insofar as the separate phases can be

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arranged to form visually attractive patterns inside a transparent container.80 The phases comprise an aqueous cleansing phase, a benefit phase, and a non-lathering structured phase. The aqueous cleansing phase must be capable of adequate lathering.81 The benefit phase comprises hydrophobic component(s) or conditioning components. These products are designed at the nanoscale: the structured phase can be a lamellar-phase formed by adding sufficient electrolytes to an appropriate surfactant. Structurants such as starch have been used in personal cleansing formulations,82 but the surfactant itself can be structured. Thus, lamellar phase does exhibit a yield stress that is sufficient to stably suspend the benefit phase. However, the yield stress of lamellar phase can vary dramatically with temperature, and, in order to overcome this problem, the cleansing and benefit phases were density matched by adding microsphere particles to reduce the specific gravity of the cleansing phase or high density particles to the benefit phase to increase its specific gravity. In this context, it is interesting that it has been recently disclosed that controlled phase separation and deposition could conceivably be achieved by loading the desired “active” phase into hollow-sphere polymer carriers,83 and again it has been reported that certain cationic guar derivatives can enhance the deposition of conditioning additives and/or solid particle benefit agents.84

Lamellar phase, especially if it is made from unneutralized long-chain fatty acids, usually displays poor dispersion kinetics and a lather that is slow to build up or slow to rinse off. However, it has surprisingly been discovered that swollen lamellar gels can exhibit both high product viscosity and fast dispersion kinetics if they are formed by combining C16-24 normal monoalkylsulfosuccinates with n-alkyl fatty acids of approximately the same chain length.85 In this context, Guth claimed a composition that was low-irritating to skin and eyes but synergistic in foaming by combining zwitterionic surfactants-fatty acid complexes with sulfosuccinates,86 and Pratley reported synergistic foaming and mildness from compositions with combinations of specific long-chain surfactants with specific short-chain surfactants and these included fatty acids and


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alkylsulfosuccinnates.87 Amine-oxide copolymers have also been claimed as suds-enhancers.88

Concentrated Cleansing CompositionsMost personal care products are based on aqueous compositions

but concentrated cleansing/personal care compositions offer the benefits of lower transportation costs, less packaging, and convenience for air travelers. If these products are solid, they must possess sufficient strength to resist the forces of extrusion during manufacture, shipping, and handling, but should disperse rapidly in water during use. Porous solid particles that are strengthened by hydrophilic polymers such as poly(vinyl alcohol) or hydroxylpropylmethylcellulose have been shown to exhibit the desired properties.89 Control of interconnectivity of the porous network is vital to this application and is described by a star volume, a structure model index, or a percent open cell content.

Conditioners Conditioning of damaged hair is commonly achieved by

treatment with aqueous formulations that contain fatty alcohols, cationic surfactants, and (optionally) silicones. These components are considered to adsorb in a hydrophilic head-down, hydrophobic tail-up conformation that confers hydrophobicity on the damaged hydrophilic hair surface. The role of a conditioner is to confer sleek lubricity and gloss on the hair. Conditioners are usually based upon cationic surfactants, and they most often are in the form of emulsions of multi-lamellar vesicles. Conditioners comprise a primary cationic surfactant, a co-surfactant, and dissolved salt.

Conventional conditioner formulations are based upon lamellar gels or emulsions using either ceto-stearyl trimethylammonium chloride or distearyldimethylammonium chloride as cationic surfactants and ceto-stearyl alcohol as co-surfactant.

As a primary surfactant, the vast majority of conventional conditioners contain either cetyl/stearyl trimethylammonium

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chloride or distearyldimethylammonium chloride. The secondary surfactant is most often ceto-stearyl alcohol.

Cetyl/stearyl trimethylammonium chloride is a conical molecule according to Ninham’s packing factor. On the other hand, ceto-stearyl alcohol consists of molecules with the approximate shape of an inverted conical molecule. The role of ceto-stearyl alcohol in a conditioner is to pack between the cationic cones and convert the micellar structure into a lamellar structure with just enough curvature to form a vesicle. Distearyldimethylammonium chloride spontaneously forms vesicles in the presence of salt, and therefore there is usually no need to add a long-chain alcohol to conditioner formulations based upon distearyldimonium chloride.

These products form a gel matrix that confers conditioning benefits from rinse-off products. They have been the basis of hair conditioners for the last half-century, and they provide excellent detangling, wet- and dry-combing, and good anti-static properties, but they can leave the hair feeing lank and greasy, and they give a long-lasting slippery feel during rinsing which is perceived by some consumers as an unclean hair feel.

Pristine hair, as it emerges from the scalp, is coated with a covalently bound layer of 18-methyleicanosoic acid (18-MEA).90-92 It has been shown that the layer of 18–MEA confers hydrophobicity and boundary lubrication on hair fibers.93 This discovery has influenced researchers to seek to include 18-MEA in conditioner formulations.94 Pristine hair shows a measured advancing water contact angle that is high, but a receding contact angle that is likewise high, and the hair tends to align. However, once the 18-MEA layer is removed, the receding contact angle is low (even approaching 0 degrees), and this corresponds to cuticle edges that are essentially hydrophilic. This means that the major differences for such 18-MEA deficient hair would be in its drying behavior rather than its wetting characteristics. The low receding contact angle would tend to “pin” the water to the hair. This would lead to longer drying times during which the capillary forces imparted by the water between hair fibers would tend to cause


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the hair fibers to clump and entangle. The inclusion of 18-MEA in prototype conditioner formulations that were based upon stearoxypropylmethylamine, dimethylaminopropylstearamide, and stearyltrimethylammonium chloride left the conditioner on the hair surface, and this in turn yielded improvements in inter-fiber lubricity due to improved deposition at the hair surface.

Conditioning Polymers in Hair Straightening Applications The two main processes for relaxing or straightening hair are

hair treatment with a reducing agent to cleave the disulphide cystine bridges (S—S) within the hair structure, and treatment of stretched hair with a strong alkaline agent.

Repeated relaxation treatments can cause significant hair damage, to both the cuticles and the cortex. The damage can be assessed by measuring the porosity of the hair, and the porosity of the keratin fibers can be measured by fixing 2-nitro-para-phenylenediamine at 0.25% in an ethanol/buffer mixture (10:90 volume ratio) at pH 10 at 37°C for 2 minutes. Cationic and amphoteric polymers, such as polyquaternium-6, polyquaternium-7, and polyquaternium-39, added to hair relaxer formulations, mitigate this degradation of the hair structure. Also, the inclusion of high molecular-weight (>106 g/mole) copolymers of acrylamide and diallyldimethylammonium chloride, acryloyloxytrimethylammoniumchloride, or acryloyloxyethyldimethylbenzylammonium chloride in the relaxing formula results in significant reduction in the hair structural damage caused by alkaline relaxation.

Conditioning PolymersCationic conditioning polymers are used to enhance the

conditioning properties, especially to mitigate the effects of extreme processing that are experienced during hair-straightening. Cationic polymeric conditioners can improve wet combability and ameliorate electrostatic charging of the hair (manifested by flyaway).

Many cationic polymers have been developed for the purpose of conferring conditioning properties on hair. In fact, there are

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now more than one hundred polyquaternium ingredients listed in the INCI dictionary, and this list is still expanding. The primary purpose of polyquaternium polymers is to confer good conditioning benefits. A non-exhaustive list of conditioning polymers is shown in Table 1.

Table 1. Examples of cationic conditioning polymers

Chitosan

Cocodimonium hydroxypropyl hydrolyzed Collagen

Cocodimonium hydroxypropyl hydrolyzed hair Keratin

Cocodimonium hydroxypropyl hydrolyzed Keratin

Cocodimonium hydroxypropyl hydrolyzed Wheat protein

Cocodimonium hydroxypropyl Oxyethyl Cellulose

Steardimonium hydroxyethyl Cellulose

Stearyldimonium hydroxypropyl hydrolyzed Oxyethyl Cellulose

Guar hydroxypropyltrimonium Chloride

Starch hydroxypropyltrimonium Chloride

Lauryldimonium hydroxypropyl hydrolyzed Collagen

Lauryldimonium hydroxypropyl hydrolyzed Wheat protein

Stearyldimonium hydroxypropyl hydrolyzed Wheat protein

polyquaternium-4

polyquaternium-10

Cationic hydroxyethylcellulose

polyquaternium-24

hydrophobically modified cationic hydroxyethylcellulose

poly(methacryloxyethyltrimethylammonium methosulfate)

poly(N-methylvinylpyridinium chloride)

Onamer M (polyquaternium-1), peI-1500 (poly(ethylenimine)

polyquaternium-2

polyquaternium-5-poly(acrylamide-methacryloxyethyltrimethylammonium ethosulfate)]

polyquaternium-6 poly(dimethyldiallylammonium chloride)

polyquaternium-7

poly(acrylamide-co-dimethyldiallylammonium chloride)


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polyquaternium-8

polyquaternium-11

[poly-(N-vinyl-2-pyrrolidone-methacryloxyethyltrimethylammonium ethosulfate)]

polyquaternium-16 [Co(vinyl pyrrolidone-vinyl methylimidazolinium chloride)

polyquaternium-17

polyquaternium-18

polyquaternium-22

poly(sodium acrylate – dimethyldiallyl ammonium chloride)

polyquaternium-27

polyquaternium-28

polyvinylpyrolidone-methacrylamidopropyltrimethylammonium chloride)

polyquaternium-31

poly(N,N-dimethylaminopropylacrylate-N-acrylamidine-acrylamide-acrylamidine-acrylic acid-acrylonitrile) ethosulfate

polyquaternium-39

poly(dimethyldiallylammonium chloride–sodium acrylate–acrylamide)

polyquaternium-43

poly(acrylamide-acrylamidopropyltrimoniumchloride-2-acrylamidopropyl sulfonate-DMapa)

polyquaternium-44

poly (vinyl pyrrolidone--imidazolinium methosulfate)

polyquaternium-46

poly (vinylcaprolactam-vinylpyrrolidone-imidazolinium methosulfate)

polyquaternium-47

poly (acrylic acid-methacrylamidopropyltrimethyl ammonium chloride–methyl acrylate)

polyquaternium-53

polyquaternium-55

poly(vinylpyrrolidone-dimethylaminopropylmethacrylamide-lauryldimethylpropylmethacrylamido ammonium chloride)

pVp/Dimethylaminoethyl Methacrylate Copolymer

Vp/DMapa acrylate Copolymer

pVp/Dimethylaminoethylmethacrylate polycarbamyl

polyglycol ester

Table 1. Examples of Cationic Conditioning Polymers (Cont.)

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pVp/Dimethiconylacrylate/polycarbamyl polyglycol ester

Quaternium-80 (Diquaternary polydimethylsiloxane)

poly(vinylpyrrolidone--dimethylamidopropylmethacrylamide)

Vp/Vinyl Caprolactam/DMapa acrylates Copolymer

amodimethicone

peG-7 amodimethicone

trimethylsiloxyamodimethicone

Ionenes

poly(adipic acid-dimethylaminohydroxypropyldiethylenetriamine)

poly (adipic acid-epoxypropyldiethylenetriamine) (Delsette 101)

Silicone Quaternium-8

Silicone Quaternium-12

Polyampholytes have been commercially available as conditioning polymers for a considerable time. A prominent example is polyquaternium-39, which is a copolymer of diallyldimethylammonium chloride, acrylamide, and acrylic acid. When this is polymerized in a single batch process, the mismatch in reactivity ratios between these monomers results in a lack of compositional uniformity. An improved version of this type of terpolymer of diallyldimethylammonium chloride, acrylamide, and acrylic acid has been made by a monomer feed method for better control of molecular weight and composition.95

Copolymers comprising a diallylamine (typically diallyldimethyl ammonium chloride) and vinyllactam monomers (typically polyvinylpyrrolidone) are useful film-formers that confer conditioning properties such as good wet and dry combability, feel, volume, and handleability.96

Silicone ConditionersSilicone quaternaries have long been known as hair conditioning

compounds.

Table 1. Examples of Cationic Conditioning Polymers (Cont.)


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A recent patent application from Evonik Goldschmidt is directed to silicone quats that confer conditioning with longer lasting conditioning through several shampoo cycles. The premise is that long-term substantivity to hair requires the conditioning agent to contain a string of cationic charges. This was achieved by Goldschmidt by polymerizing cationic monomers and grafting them to silicone backbones. In general, water-soluble monomers polymerized in the presence of silicones yield a mixture of water-soluble polymers and unsubstituted silicones because the two ingredients are incompatible and attachment of the polymer chain to the silicone would require appropriate “coupling groups.” The Evonik researchers rose to the challenge by polymerizing the cationic monomers in the presence of silicone polyethers. The ether groups are compatible with the quat monomers, and they readily chain transfer to give graft copolymers. Once grafted, the copolymers are quaternized to confer permanent positive charges with enhanced substantivity to hair. The grafts are obtained by polymerizing the readily available monomers, dimethylaminoethylmethacrylate, or 3-trimethylammoniopropyl-methacrylamide.

Leave-on silicone conditioners specifically targeted to non-shampoo applications confer enhanced and relatively durable conditioning. These contain emulsified vinyl-terminated silicones applied in combination with a conventional cationic conditioner. A preferred product type is a mousse. These silicone block copolymers can achieve excellent conditioning at relatively high viscosities (100 KPa/s-1).

Improved conditioning that confers surprisingly reduced friction on hair can be achieved by including an aminosilicone in which the aminosilicone has a fairly large range of average particle sizes from about 5–50 microns.97

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