Colloid & Surface PhenomenaCE457/5274/9/2002

Moisturizing Lotion

Jason AshberyJonathan DannerHaohao HuangLeigh Vorreuter

I. Introduction

The general title cosmetics are applicable to a wide array of products. Some cosmetics

such as blush or eye shadow are used to enhance the color of the person’s eyes or cheeks.

Other cosmetics are used to protect the skin, for an example to delay the aging process.

Some examples are lotion, creams, and sunscreen. Each one is different and carries

different responsibilities.

Lotion can hold many different responsibilities. Lotion is considered a cosmetic product.

It should improve the skin and have many useful purposes. Some lotions contain

sunscreen that contains UV protecting agents that may reflect the harmful affects of the

sun. Other lotions contain alpha hydroxides that improve the appearance of the skin.

These beneficial attributes need help to deliver the wanted components to the skin and

cause adhesion to the skin and also penetrate the skin.

There is a huge assortment of lotions to assist in customer’s needs. Some people prefer

scented lotions compared to unscented. Others like quick absorbing lotion. Lotions

sometimes need to be very sensitive to a person’s skin. A person may need lotion to heal

dry skin while another might use it to prevent dry skin. Some women may feel like their

skin has aged and some “age defining” lotion can help the skins appearance. There are

many different varieties of lotions for instance; for dry skin, for extra dry skin, and for

sensitive skin. Some contain sunscreen and others have desired fragrances.

They are many different manufacturers of moisturizing lotion. The manufacturers market

their products towards age and gender. A young girl would be more likely to buy from

Bath & Body Works because they have lotions that are scented and their labeling is

colorful and attractive. Men on the other hand prefer non-scented lotions. Keri and Curel

make non-scented lotions. Other manufacturers such as Bristol-Meyers Squibb lean more

towards the pharmaceutical side of lotions.

The manufacturers have product specifications related to customer needs. These

specifications are very important towards the characteristic of the lotion and are usually

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over looked by the customer. The lotions need to have an appropriate shelf life and it

needs to have a good physical and chemical stability as well as cosmetic appeal. This is

essential for any lotion because if the lotion has a short half-life the mixture will separate

and not be able to be used. It also needs to reach its goal of moisturizing which means

the active ingredients need to reach the desired target. The lotion has to be non-irritating

to the skin and the pH needs to be a consideration. Lotions also must be fast absorbing

and non-greasy. The duration that the lotion stays on the skin is important. It also needs

to be long lasting. The lotion needs to go on smoothly and evenly and removed from the

skin when it is appropriate.

The product design considerations are an essential part of the manufacturing process and

the formulation of the moisturizing lotion. A manufacturer must identify their consumers

needs are establish the appropriate product specifications in order to be successful.

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II. Components and Composition

There are many different brands of moisturizing lotion on the market today. Most

manufacturers also make several different formulations of the same brand. The result is a

relatively large number of formulations for the consumer to choose from. It is important

to realize however, that most of the lotions being sold share several of the same

components. Two major differences between competing brands are noted in this section.

Component listings may vary significantly from product to product based on the color

and scent of the lotion. These various fragrances and dyes may seem to monopolize the

ingredient list, but they are only present in extremely small percentages.

The second difference is definitely not as obvious as the first. Lotion manufacturers use

various surfactants to enhance product performance. Common ingredients names for

these surfactants include the following: Laureth-23, Ceteareth-20, Quarternium-15, and

Dimethyl Distearyl Ammonium Chloride to mention just a few. Manufacturers may also

include alpha-hydroxy acids such as glycolic and lactic acid.12

The following table was created using the ingredient listings located on the backside of

the bottles. It is presented in this format to further illustrate how many brands share

common components. For simplicity, ingredients listed on only one of the five lotions do

not appear in the table. Note that surfactants vary from product to product and may not

be included in this list.

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Table 1.Common Components Present in Different Brands of Moisturizing Lotion*    Suave Bath & Body Bristol The Andrew Body Benefits    Works Meyers Jergens Co.  Water X X X X XGlycerin X X X X X(Tetra, Tri, or Di-) sodium EDTA X X X   XDimethicone X X X X XCarbomer X X X    Tocopheryl Acetate (Vitamin E)   X X   XAloe gel X X     XPetrolatum X X X X  Glyceryl Stearate X       XSodium Hydroxide   X X    Methylparaben X X   X  DM DM Hydantoin X       XBenzyl Alcohol   X X    Magnesium Aluminum Silicate X   X    Propylparaben X     X  Mineral Oil X        Isopropyl palmitate       X XCetyl Alcohol   X X X  Cetearyl Alcohol   X     XCeteareth-20   X     X  * Components present in only 1 of the 5 lotions are not listed here. 

The primary ingredient in most moisturizing lotions is de-ionized water. It can be

expected that water comprises anywhere between 60 and 95 weight % of the lotion.

Following is a graphical display of the composition of a particular formulation of

moisturizing lotion taken from U.S. Patent # 6,017,548 assigned to The Andrew Jergens

Company.12

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Table 2.Approximate Composition of a Lotion Patented by The Andrew Jergens Company (U.S. Patent# 6,017,548)

Chart # Components Approx. % Weight1 Water 93.22 Glycerin 2.43 Dimethyl Distearyl Ammonium Chloride 14 Petrolatum 0.85 Lactic Acid 0.66 Isopropyl palmitate 0.67 Cetyl Alcohol 0.58 Glycolic Acid 0.49 Dimethicone 0.310 Ammonium Hydroxide 0.211 Methylparaben 0.0212 Propylparaben 0.008

Graph 1.

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III. Colloids and Surface Interactions

Throughout the diverse moisturizing lotions that are sold today there exist common

ingredients that perform key universal functions to moisturizing lotions. The most

abundant of these ingredients is water, whether it is purified or deionized. Since

moisturizing lotion is an oil-in-water emulsion, water is the continuous phase and

functions as the diluent. Glycerin (C3H8O3) serves as the humectant, which adds moisture

to the stratum corneum, which is the skin, and helps to soften the skin 12. Silicone fluids

are also utilized in lotions as an emollient or smoothing aid. They improve the lubricity

of the moisturizing lotion when it is applied to the skin 12. An example of a commonly

used silicone fluid is Dimethicone (C2H6OSi). Petrolatum and/or mineral oil are added to

the emulsion to serve as an occlusive emollient. These hydrocarbons form a hydrophobic

film on the surface of the skin, which prevents water loss from the skin to the

environment. It traps the moisture in the skin. Disodium EDTA functions as the

chelating agent 16, and carbomer, a carboxyvinyl polymer, acts as a thickening and

emulsifying agent. A key difference among various lotions is the type of

surfactant/emulsifier used. Despite the use of different emulsifiers the basic the function

of the amphiphile remains the same, which is to stabilize the oil-in-water emulsion by

acting at the oil-water interface. One example of the surfactant used in Keri Fragrance

Free Lotion is Quaternium-15, which is a cationic emulsifier.

In addition to the universal ingredients, many other molecules become a part of lotion.

These might include fatty alcohols such as cetyl alcohol, which combined with the

surfactant aid in stabilizing the emulsion 5. Further examples include nutrients such as

tocopheryl acetate (Vitamin E), preservatives, and fragrances. Some of these

components, for Keri Fragrance Free Lotion, along with their basic functions are shown

below in Table 3.21

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Table 321

KERI FRAGRANCE FREE LOTIONComponent Basic Function

Water diluent Glycerin humectant Dimethicone * emollient, smoothing aid Petrolatum * occlusive emollient Disodium EDTA chelating agent Carbomer * thickening agent, emulsifying agent Quaternium-15 * cationic surfactant, cationic emulsifier Cetyl Alcohol * emollient, emulsion modifier, coupling agent Tocopheryl Acetate (Vitamin E) * nutrient Steareth-2 * emulsifier, wetting agent Aloe gel nutrient Benzyl Alcohol antimicrobial Laureth-23 * emulsifier, wetting agent Magnesium Aluminum Silicate thickening agent Sodium Hydroxide alkalizer, pH adjuster* = "colloidal" sized molecules

A. Liquid/ Liquid Emulsion

Moisturizing lotion is a liquid-liquid emulsion. An emulsion is formed when a mixture

of two immiscible liquids are separated by a surfactant molecule, which lines the

interface of the liquids. The surfactants are amphiphilic molecules composed of a

hydrophilic polar headgroup and a “hydrophobic” nonpolar tail. When placed into an oil-

water solution, the amphiphiles spontaneously aggregate at the oil-water interface to

minimize unfavorable interactions. They do so by orienting themselves in such a manner

that their headgroups point into water while their nonpolar tails point into the oil. In a

microemulsion of oil-in-water, O/W, the surfactants form droplets of oil in water.

Likewise a microemulsion of water droplets in oil, W/O, can also be attained, where the

surfactant headgroups point into the water and the nonpolar tails face outward into the

oil. Depictions of an O/W (a) and W/O (b) microemulsion are shown below in figure 1.

below 1.

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Figure 1

Moisturizing lotion is an oil-in-water, O/W, emulsion. However, the process of making

lotion begins with a W/O emulsion. During the mixing procedure, a phase inversion

occurs changing W/O to O/W. There are at least three possible factors that can be altered

to achieve this phase inversion. They are: (1) temperature, (2) surfactant composition,

and (3) water concentration.

The temperature of the emulsion can lead to a phase inversion if temperature sensitive

emulsifiers, such as ethoxylate emulsifiers, are used as surfactants 9. Ethoxylate

emulsifiers become less hydrophilic when heated. Therefore, emulsions that use them

change achieve a reversible phase inversion from O/W to W/O at a well-defined

temperature, called the phase inversion temperature (PIT). “Cosmetics O/W emulsions

with improved stability and small droplet size can be manufactured by producing a W/O

emulsion at high temperature and cooling through a phase inversion” 9. This technique of

varying the emulsion temperature only leads to a phase inversion if ethoxylated

surfactants are used. This is because other types of surfactants do not show a significant

sensitivity to temperature change 9.

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The surfactant composition in the emulsion can also be altered in order to achieve a phase

inverse. For example, consider a W/O emulsion that is generated using a hydrophobic

emulsifier and to which is added an aqueous solution of hydrophilic surfactant. At low

hydrophilic surfactant concentration the system remains as a W/O emulsion. However,

as the hydrophilic concentration increases, the system will eventually undergo a phase

inversion from a W/O to an O/W emulsion 9.

Finally, a third variable that can lead to a phase inversion is the water concentration in the

emulsion. Starting with a W/O emulsion, if a sufficient amount of water is added to the

system, a catastrophic phase inversion will occur resulting in an O/W emulsion 9. This is

the technique by which the Andrew Jergens Company prepares moisturizing lotion:

The oil-in-water emulsions of this invention are prepared by first forming an aqueous

mixture of the water-insoluble component and the humectant. The water-insoluble

components include the cationic emulsifier, the petrolatum or mineral oil component, the

fatty alcohol component, the fatty ester emollient, and the silicone component. The

components are preferably added to water in the following sequence: humectant,

petrolatum/mineral oil, fatty ester, silicone oil, fatty alcohol. After these components are

thoroughly mixed, the cationic emulsifier is added to the aqueous moisture at a

temperature of about 80 to 95 degree C. under agitation to form a water-in-oil emulsion.

The input of the mixing energy will be high and will be maintained for a time sufficient

to form a water-in-oil emulsion having a smooth appearance (indicating the presence of

relatively small micelles in the emulsion). Water is then directly injected into the

emulsion to cool it to a temperature of about 45 to about 60 degree C. The temperature is

critical. Unstable emulsions result if the temperature drops below about 45 degree C.

Higher temperatures promote unacceptable water loss through evaporation. During this

quench step the emulsion, initially water-in-oil, inverts to form an oil-in-water

emulsion.12

B. The Effect of Amphiphiles on Delivery to the Skin

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One type of surfactant used in moisturizing lotions is the cationic surfactant; positively

charged molecules in solution. The behavior of ionic micelles can be explained by

‘hydrophobic’ tail and headgroup characteristics. As the temperature of the emulsion

increases, the critical surfactant concentration for micelle formation (CMC) increases and

the number of amphiphile molecules per micelle (No) decreases. The increase in

temperature leads to a greater repulsion between headgroups, resulting in a higher Gel, a

higher Gmic, and an increase in CMC. 1 Gel is the free energy associated with purely

electrostatic interactions arising from headgroup repulsions. Gmic is the free energy of

micelle formation. Ultimately, the increase in temperature decreases the stability of the

emulsion by decreasing the stability of the micelles. Furthermore, the addition of salt

lowers the CMC while increasing the No. Adding salt has the opposite effect on ionic

micelles than raising the temperature. 1

The effect of temperature on ionic micelles may also effect the mechanism of

moisturizing lotion on the skin. While the exact mechanism is not entirely understood, it

is believed that the temperature change that occurs when the lotion is applied to the skin

induces a phase change; causing the humectant (glycerin) to move from the micellular

interface to the external surface of the emulsion. The humectant is then able to transfer to

the stratum corneum in order to moisturize the skin12. Perhaps the higher temperature of

the skin destabilizes the micellular structure, releasing the humectant inside.

Cationic surfactants are not the only type of emulsifiers that are used to prepare

moisturizing lotion. For example Noveon has formulated a moisturizing lotion with

Pemulen polymeric emulsifiers. Pemulen emulsifiers have the ability to form long-

term stable O/W emulsions that have a triggered release mechanism. “Pemulen

emulsifiers instantly deswell upon contact with the electrical charge on the skin to release

the oil phase and provide immediate coverage, eliminating the lengthy lag time seen

using traditional surfactant systems.”16 In traditional surfactant systems liquid crystals

made up of oil, water, and surfactant are formed and are deposited on the stratum

corneum. These liquid crystals temporarily prohibit the oil phase from being released to

the skin so that it cannot form a desired occlusive film. The crystals can last for up to 90

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minutes before they are degraded due to the evaporation of water from the liquid crystals

to the environment. An illustration is shown below, Figure 2, comparing the application

of traditional surfactant systems to emulsions formulated with Pemulen polymeric

emulsifiers. 16

Figure 2

Unlike cationic surfactants, Pemulen appears to be electrically sensitive rather than

temperature sensitive. Cationic surfactants and Pemulen are examples of how the use of

different surfactants directly influences the mechanism by which moisturizing lotion aids

the skin.

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IV. Product Attributes

The colloids, polymers, and surfactants enhance and affect the product specifications.

Each ingredient serves at least one purpose. Many of the ingredients have multiple

purposes. For the four chosen moisturizing lotions one can see the similar components.

Water is the main component of lotion and its main purpose to serve as a diluent.

Dimethicone, Glycerine, EDTA, and Carbomer serve many different basic functions for

example as emollients, humectants, chelating agents, and thickening agents. In Table 3

Keri fragrance free lotion shows its main functions of its ingredients.

Some examples of colloids and polymers that enhance the affect the product specification

are described. Dimethicone is a silicone fluid mixture that enhances the durability, gives

a nice soft feeling and is also an anti-whitening agent. It gives the skin a pleasant shine.

Laureth-23 is a non-ionic emulsion that is often used as a conditioning agent in lotions. It

gives skin luxurious feeling when applied. Fatty acids such as Benzyl or cetearyl alcohol

thicken and stabilize the lotion. 5

The functionality of primary ingredients in relation to customer needs is one of the most

important characteristics of lotion. The lotion’s shelf life, absorption properties,

consistency, and fragrance are altered through different colloids, polymers, and

surfactants. Also sunscreens, alpha hydroxide, slow release of fragrances, and prolonged

hydration properties are achieved by different colloidal particulate systems.8

The shelf life of moisturizing lotion is extremely important. A company can estimate the

amount of time it takes for a bottle to be bought. Once the bottle is bought it could take

up to a year to finish and it all depending on the amount of lotion in the bottle. Bigger

bottles of lotion are much more economically efficient, but no one would buy the lotion if

it were going to go “bad”. This is why the shelf life is such a crucial part of lotion.

Adjusting the hyrdophile and lipophile balance of the emulsifier is a very important

aspect for achieving emulsion stability. 12 Emulsions prepared with hydrophobically

modified water-soluble polymers are stable for years. The lotion’s dermatological

emulsions are thermodynamically unstable due to its positive interfacial energy. When

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the emulsion tries to reach its thermodynamic equilibrium it causes the emulsion to break

up back into its component phase. In order for the product to be able sustain it shelf life

qualities, the formula must attempt to delay the separation process. The delay can be

accomplished by adding specific mixed emulsions compiled of ionic or non-ionic

surfactants combined with fatty amphiphiles (Table 4). 5

Table 4Fatty amphiphiles SurfactantsCetostearyl alcohol Sodium lauryl sulphateCetyl alcohol CetrimideStearyl alcohol Cetomacrogol 1000Glyceryl monostearate PEG 1000 monostearateStearic acid Triethanolamine stearatePhosphatidylcholine Sodium stearate

Incorporating previously blended emulsifying wax into the formulation can also prevent the separation of the emulsion. Some wax and its components are represented in Table 5.

Table 5Emulsifying wax Component

Emulsifying wax BPCetostearyl alcohol, sodium lauryl sulphate

Emulsifying wax USNF Cetyl alcohol, polysorbateCationic emulsifying was BPC Cetostearyl alcohol, cetrimideGlyceryl monostearate S.E. Glyceryl monostearate, sodium stearateCetomacrogol emulsifying wax BPC Cetostearyl alcohol, cetomacrogol 1000Polawax Cetyl alcohol, non-ionic surfactant

The gel network theory of emulsion stability is why both emulsifiers and mixed

emulsifying wax give their desired results. “The theory relates the structure and

properties of liquid and semisolid emulsions to the swelling properties of a lamellar,

crystalline gel network phase formed when the mixed emulsionfier, in excess of that

required to stabilize oil droplets, interacts with continuous phase water.” 5

These emulsifiers must stabilize the oil droplets at the manufacturing point by the

formation of an interfacial film. This is simply controlling the rheolgical properties of the

formulation.

The lotion’s consistency is due to swelling properties and concentration of the α-

crystalline gel phase. The gel phase is a lamellar structure of alternating bilayers of

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emulsifying wax separated by layers of water. When the α-crystalline form is in the

presence of very small quantities of ionic surfactant and a fatty alcohol is dispersed in the

water the amount of swelling increases which leads to the swelling of the α-crystalline

gel phase. The water that is in between the bilayers of the gel phase is essentially bound

water and this increases the volume ratio of the dispersed phase to the free continuous

phase water. This causes the system to thicken. 5

The evaporation and absorption of lotion is a very complex system. When lotion is

applied to skin thinly, emulsion destabilization often occurs during the use. When a

dermatological emulsion is rubbed onto the skin water evaporates and the oil droplets

coalesce.5 Coalesence occurs when the interaction energy between substrates and

adatoms is small, clusters can detach them selves from any given location on the surface

and diffuse as entities over the surface. The clusters behave more like liquid droplets than

solid crystallites when they coalesce. They can even liquefy, but re-solidify immediately

after to assume the prior configuration.1 After the application of the lotion the

composition will change as water and other volatile solvents evaporate. The film stays on

the skin to protect it and the drug is absorbed into skin. 5

The viscosity of moisturizing lotion is another very important attribute. Emulsion size

plays a big role with the lotions viscous properties. An experiment was completed where

the shear stress dependence of the apparent viscosity of monodisperse emulsions with

different droplet size and concentrations was measured. The viscosity increased with the

increasing droplet concentrating. At the same shear stress and droplet concentration the

viscosity of concentrated emulsions containing smaller droplets was significantly greater

than emulsions containing larger droplets. This suggests that electrostatic repulsion plays

an important role in determining the rheology of concentrated emulsions. The droplets

become closely packed causing the emulsions to be come rigid at lower concentrations

for smaller droplets because of their effective volume fraction is greater.10 This explains

why low emulsifier concentrations are good for structured lotion.5 Viscosity is very

important when it comes to differentiating between creams and lotions. Lotions are used

on large body parts like legs and arms. Consumers like their lotion to glide easily.

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Therefore a less viscous moisturizer would be ideal. Also absorption capacity on the skin

increases with decreasing viscosity.2

Fragrances in cosmetics especially lotion are very important. People base their decision

to buy a product by the way it smells and how long the duration of the fragrance last.

Fragrances for skin care products are applied in colloidal systems like emulsions. The

lipid part of the stratum corneum is organized in lamellar structures. The lamellar liquid

crystals in lotions contain the fragrance molecules. The similarity of the configuration of

the crystals in lotion compared to the stratum corneum is why it easy for the fragrance to

be absorbed into the skin. The location of the interlayer spacings and the geometrical

characteristics play a big role on where the location of the fragrance is. Also the

biomembranes are related to the delay of the disappearance of the fragrances.

A main reason consumers buy cosmetic lotions is to help their appearance of their skin.

Liposomes have positive effects on the appearance of the skin. They improve cutaneous

hydration and skin structure. They also decrease the depths of wrinkles and decrease eye

puffiness. Liposomes are spherical vesicles that have an aqueous cavity at their center.

They are used to carry water-soluble molecules and hydrophobic molecules. These have

the ability to be incorporated within the bilayer membrane. Liposomes have been

evaluated as delivery systems for drugs, vitamins and cosmetic materials. Liposomes can

be custom designed for almost any need by varying the lipid content, size, surface charge

and method of preparation. The liposomes have a structure similar to the cutaneous cells

therefore they can interact with each other and they can supply phospholipids to the skin.

The phospholipids are what the skin needs to improve it.8

Particulate systems are very small particles that range from micrometers to millimeter.

These particles deliver essential active ingredients such as amino acids, plant extracts,

minerals, vitamins, antioxidants, and UV protectants. These particles function is to

deliver the ingredients to the upper layer of the skin. They also prolong the time during

which the ingredient remains on the skin. This is important with sunscreens because one

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doesn’t want to have to reapply it every hour. It is also incorporated with the time release

of fragrances and prolongs the hydration properties. 8

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V. The effluence of structure of moisturizing lotion (texture parameter) on its use properties, and control of its physical properties

The texture parameter (its physical characterizing parameter) is related to the properties

of moisturizing lotion and consumer’s acceptance. Table 1 provides the relations

between some texture parameters and popular nomenclature. [17]

Table 6. Texture profile [17]Primary parameter

Secondary parameter

Popular terms

Mechanical characteristics

hardness Soft→firm→hardCohesiveness Crumbly→crunchy→brittleviscosity Thin→viscouselasticity Plastic→elasticadhesiveness Sticky→tacky→gooey

Geometrical characteristics

Particle size and shapeParticle shape and orientation

Gritty, grainy, coarse, etc.Fibrous, cellular, crystalline, etc.

Other characteristics

Moisture content

Dry→moist→wet→watery

Fat content Oilinessgreasiness

oilygreasy

From the table above, we can believe that the consumer’s sensory description of the

lotion has close relation with the texture structure and physical parameters. The skin care

product evaluation is also related with the texture profile parameter, shown in Table 2.

According to the introduction above, the physical characteristics, especially rheological

behavior of lotion is very important to its properties. We should control the rheological

behavior of lotion. There are some important factors will affect the rheological behavior

of lotion.

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Table 7. texture profile parameter used in the skin care product evaluation [17]

Stage of evaluation Skin care product attribute and definite

Texture profile parameter

PICK-UP, product removed from container, product poured or squeezed from bottle onto fingertips, or product lifted from jar with forefinger

THICKNESS-perceived denseness of product. Evaluated as force required to squeeze between thumb and forefinger. Rated as thin-medium-thick.Or: CONSISTENCY-perceived structure of product. Evaluated as resistance to deformation and difficulty of lifting from container. Rated as light-medium heavy.

Viscosity for lotions

RUB-OUT (application), spread of product over and into skin with fingertips using gentle circular motion at a rate of two rub per second for a specified period of time, depending on the product.

SPREADABILITY-ease of moving product from point of application over rest of face. Evaluated as resistance to pressure. Rated or described as:‘slips’-very easy to spread‘glides’-moderated easy‘drag’-difficult to spread

ABSORBENCY-Rate at which product is perceived to be absorbed into skin. Evaluated by noting changes in character of product and in amount of product remaining (tactile and visual) and by changes in skin surface. Rated slow-moderate-fast.

Viscosity, cohesiveness, springiness, gumminess, adhesivenessOther characteristics –(oil and water content of product)

AFTER-FEEL (and appearance), evaluation of skin surface with fingertips, visually and kinesthetically immediately after product application and possible at varying intervals thereafter.

AFTER-FEEL – Type and intensity of product residue left on skin; changes in skin feel/ Product residue is described by type, i.e. film(oily or greasy), coating(waxy or dry), flaky or powdery particles; the amount of such residue is identified as slight-moderate-large.Skin feel is described as dry (taut, pulled, tight); moist (supple, pliant), oily(dirty, clogged).Other sensations are also noted and identified where applicable, i.e. clean, stimulated, irritated, etc.

Other characteristics-(oil and water content)

Geometrical characteristics-(gritty, powdery, etc.)

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1. Factors influencing the lotion physical parameter [18]

(1). THE EMULSIFIER[18]

The emulsifier frequently is the most important role in the emulsion in producing the

characteristic flow properties. In dilute emulsions this is more evident because when the

concentration of emulsifier is varied, the effects of change in particle size and particle

size distribution of the disperse phase on the viscosity of the emulsion are not as big as

the change in the viscosity of the continuous phase brought about by the emulsifier.

Mixed emulsifiers can provide desirable flow properties (used to thicken lotion, see also

table 2) and to reduce cream of lotion.

(a) Hydrophilic polymer emulsifier: the study has gotten the apparent pseudoplastic

viscosity for these hydrocolloids from plot of log (shear rate) vs. log(shear stress).

(b) Mixed emulsifier: In O/W emulsions the viscosity can be affected by type and

amount of interaction between a lipophilic and hydrophilic emulsifier placed in

the oil phase or aqueous phase. In addition, supplementary use of fatty acids or

alcohols in the oil phase can modify the rheological parameters of emulsion.

The cetyl alcohol emulsion was mobile after 20 days and exhibited only slight creaming.

Particle size of the emulsions were similar and the theological stabilities showed no

relation with variations in particle size distribution but there is a relation with the stability

of the viscoelastic network in the aqueous phase at 25º

The chain length of the alcohol can affect the mobility of lotion. After preparing

immediately, the tetradecanol (C14) and hexadecanol (C16) emulsion became semisolid

and of similar consistency. The octadecanol (C18) stabilized emulsion was extremely

mobile, but the cetosteayl alcohol emulsion showed properties of all three emulsions

containing the pure alcohols.

The effect of concentration of emulsifier cannot explain emulsion behavior of lotion

without taking into account secondary effects such as the particle size and particle size

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distribution, which also exert a pronounced influence on the flow properties of lotion.

Studies have shown that the viscosities of concentrated emulsion increase to a greater

extent than the viscosities of comparable dilute emulsions when the concentration of the

emulsifier is increase. 19

(2) THE DISPERSE PHASE 18

There are many parameters related to the disperse phase or internal phase that exert

rheological changes in emulsions, including: nature of the oil; viscosity of the oil; particle

size; particle size distribution; and particle shape. Particle size and particle size

distribution also depend on the emulsifier concentration.

The nature of the oil in O/W emulsion exerts its effect on the emulsion via its interaction

with the emulsifier. The viscosity of the aqueous medium and the particle size

distribution are related to differences in the state of aggregation of the globules.

The mean particle size and particle size distribution can exert profound effects on the

rheological parameters of an emulsion. The viscosity of dilute O/W emulsions are

influenced by mean particle size variation of 3 to0.7 microns, but in concentrated

emulsions the product of relative viscosity and mean particle size did not change if the

distribution of particle size about the mean value was not very wide.

(3) THE CONTINUOUS PHASE

The rheological behavior of a lotion is most often determined by the rheology of the

continuous phase. The rheological behavior of the continuous phase of O/W emulsions is

frequently controlled by the use of hydrocolloids, which have been already been

discussed. The rheological behavior properties of the emulsion, in turn, are dependent on

the stability of the hydrocolloidal system.

(4) PHASE VOLUME RATIO

The rheological patterns of dilute emulsions are often markedly different than those for

concentrated emulsions. Therefore, it is useful to have information concerning the

viscosity dependence on the phase volume ratio in both areas. Generally, it has been

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found that the rheological parameters of an emulsion increase with increasing the phase

volume ratio. It is expected that the limit of φ before inversion occurs will vary

depending on the characteristics of the system and, in particular, the nature of the

emulsifying agent and its solubility in the continuous phase of the emulsion.

2. The effects on the behavior of lotion during lotion processing 20

During the processing, we should control the effect in order to get ideal end properties of

lotion. (For processing detail, see also part II)

(1) Mixing

Mixing is a basic step to the compounding and processing of lotion in the cosmetic

industry. Mixing is necessary to blend a water phase and oil phase into an emulsion, but

consider the potential effect of the degree of mixing on the product viscosity. First of all,

a minimum of energy must be used to evenly mix the two phases and other additives. A

high amount of mixing energy, however, can decrease the particle size of the dispersed

phase and hence affecting the emulsion viscosity. The timing of this mixing energy can

also be important, as the product is finished off and cooled to filling temperature. In the

case of a lotion, which is usually cooled to room temperature, viscosity can increase

tremendously when the product is cooled. If the mixing energy is kept constant during the

cooling cycle, it begins to have more of an effect as the viscosity increases. This means

that a short period of mixing at 90F can have a greater effect on viscosity than a long

period at 150F. If the product is shear-thinning (pseudoplastic or thixotropic), the

viscosity reduction is not completely reversible.

The mixer in the plant should be suitable to the mixing requirements of various lotions.

Not only can the mixer affect the product viscosity, but the product viscosity can also

affect the degree of mixing. If a propeller is utilized to mix a viscous product that is

shear-thinning, it will cut a hole in the center and leave the bulk of the product unmixed.

If a product happens to be shear-thickening, it could gradually build up in viscosity to the

point where the mixer motor is overloaded.

In case of heat transfer, viscous lotions are usually handled with a contrarotating agitator.

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Mixing is so basic to the formation of the lotion and can have such an important effect on

product rheology that the smart formulator will learn to work with it in achieving the

desired end properties instead of fighting against it in a dogmatic scaleup from benchtop

to plant. Cosmetic lotion may be shear sensitive to some degree and mixing can be used

as a tool in achieving the desired product viscosity by properly manipulating the mixing

variables.

(2) Heating and cooling

Heating is generally less of a problem in cosmetic processing because the product or

phase is usually fluid at elevated temperatures (viscosity being inversely proportional to

temperature for emulsions commonly encountered in the cosmetic industry). The rate of

heating is not usually considered an important parameter, assuming that the desired end

point is not overshot.

Cooling is more commonly a problem with cosmetic emulsion because it generally

increases product viscosity greatly.

In summary, a lotion is usually heated after it has been formed to reduce its viscosity for

filling. Cooling has a more important relationship to final product viscosity because of its

effect on crystallite size and dispersion, and because of the interrelationship of work input

and product viscosity.

(3) Shearing

Many lotions are shear-thining. In a typical operation, a finished lotion is cooled to room

temperature in a compounding vessel, and then pumped through a filter to a storage tank

where it is held for filling. The viscosity of lotion will have been reduced by this step.

Then the product may be pumped to the filling line. The product usually has a chance to

build a network of bonds. A portion of these bonds, if broken, are sometimes

permanently destroyed.

(4) Homogenizing

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Homogenization, or the reduction of particles to a small and uniform size and their even

distribution in a medium, is related to shearing in that frequently used to create the

particle breakdown. The cosmetic industry usually resorts to homogenization for

dispersing solids and insoluble liquids in a liquid phase and reducing the dispersed

particles to a minimum size. The reasons for doing this are numerous and include the

desire to increase stability by minimizing globule size and hence decrease the chances of

coalescence, to reduce particle size of the disperse phase so as to inhibit settling, and to

increase viscosity by forming a finer emulsion. If while the emulsion is hot and both

phases still liquid, homogenization will tend to reduce the disperse phase to a minimum

size distribution which will impart certain properties (such as increased stability) to the

final product when it is cooled down and packaged. If the product is homogenized after

some cooling has taken place and viscosity has already started to build, however, the

viscosity of the finished product may be permanently reduced. Timing and process step

must be considered in developing a process to make a product with the desired end

properties.

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VI. Final Product Considerations

a. Manufacturing Process

The objective of the manufacturing process is to disperse one liquid within another in an

extremely fine form to make certain that separation due to settling either does not occur

or takes place very slowly. The process does not normally involve any extraction or

chemical reaction. 4

Shear rate plays a major role in liquid-liquid emulsion formation. Another parameter

which influences emulsion formation is whether there are sufficient stabilizers present to

maintain the smallest droplet size produced for long periods of time. Blend time and the

standard deviation of circulation time also influence emulsion formation. These are only

a few of the many variables that make it difficult to specify a mixing process based on a

desired droplet size. However, if data are available for a particular mixing system then

appropriate correlations can be used to try and predict droplet size formation based on

different variables. 4

An example of a typical manufacturing process is as follows12:

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b. Federal Rules and Regulations

Current Good Manufacturing Practices are written and enforced by the Food and Drug

Administration. The primary objective of these guidelines is to ensure that manufacturers

provide consumers with safe and effective products. More specifically, Parts 210 and

211 apply to the manufacturing, processing, packaging, and holding of drugs and finished

pharmaceutical products. Moisturizing lotion is not a typical pharmaceutical pill or

capsule, however it is applied directly to human skin is therefore subject to the same

manufacturing criteria.

Part 211 includes a description of the responsibilities of a quality control unit. The

quality control unit is responsible for the chemical analysis of all raw materials,

intermediate, and finished products. In the case of raw materials, vendor Certificates of

Analysis (COA) may be used in place of chemical analysis. The COA may me used only

after the quality control laboratory has certified the vender.3 Quality control is

responsible for microbial testing of finished products. In addition to this, product

stability tests are mandated and normally performed by the quality control unit. Product

stability tests are used to identify trends that essentially determine the testing limits for

finished products.

Final product testing for moisturizing lotion typically consists of but is not limited to the

following: Physical Description (Texture, Color, Odor), Specific Gravity, Viscosity, and

pH. Any individual batch of product should not look, smell, or feel different from what

the consumer would consider normal. The specific gravity of the lotion should be

relatively close to unity. Viscosity may vary significantly from brand to brand but it

should be such that it does not inhibit delivery from the package or bottle. The pH of the

final product is normally close to the skins natural pH of 6.16 Raw material testing is

more extensive and beyond the scope of this project.

Current Good Manufacturing Practices, Part 211, also indicates that all personal need to

be adequately trained or experienced to perform responsibilities delegated unto them.

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This training should be properly documented. Buildings and facilities are to be designed

and maintained with cleanliness in mind. Proper lighting, ventilation, and plumbing are

considered necessities. Equipment should be properly cleaned and maintained.

Components used in product formulation are to be stored in a manner that prevents cross

contamination and material degradation. Containers need to be adequately labeled and

each step of the manufacturing process should be documented in a batch record. Batch

records should be kept throughout the product’s shelf life. Part 210 provides the

manufacturer with an overview and some definitions used in Part 211.

c. Marketing Considerations

Women comprise the majority of the consumer target group for the sale of moisturizing

lotion. In addition to utility, packaging aesthetics, fragrance, and color weigh heavily in

the lotion selection process. Shelf location is also significant. Products displayed at eye

level have a greater chance of being selected. In summary, product sales may be

influenced just as much by aesthetics as they are by actual product functionality.

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REFERENCES

1. Evans, Fennell and Stokes, Robert.; Fundamentals of Interfacial Engineering, Wiley, Canada 1997.

2. Brummer, R. and Godersky, S.; Rheological studies to objectify sensations occurring when cosmetic emulsions are applied to the skin, Colloids and Surfaces A: Physicochemical and Engineering Aspects, Volume 152, Issues 1-2, 15 July 1999, Pages 89-94

3. Code of Federal Regulations, Food and Drug: Parts 210 and 211, April 1, 2001

4. Perry, R. H. and D. W. Green (eds.), Chemical Engineering Handbook, 7th ed., McGraw-Hill Book., New York 1997.

5. Eccleston, G. M.; Functions of mixed emulsifiers and emulsifying waxes in dermatological lotions and creams, Colloids and Surfaces A: Physicochemical and Engineering Aspects, Volumes 123-124, 15 May 1997, Pages 169-182

6. J. N. Israelachvili: Intermolecular and Surface Forces, 2nd ed., Academic Press, 1992.

7. M. J. Rosen: Surfactants and Interfacial Phenomena, 2nd ed., Wiley, 1989.

8. Magdassi, S.; Delivery Systems in Cosmetics, Colloids and Surfaces A: Physicochemical and Engineering Aspects, Volumes 123-124, 15 May 1997, Pages 671-679

9. Miller, D. J.; Henning, T.; Grunbein, W; Phase inversion of W/O emulsions by adding hydrophilic surfactant – a technique for making cosmetic products, Colloids and Surfaces A: Physicochemical and Engineering Aspects, Volumes 183-185, 15 July 2001, Pages 681-688

10. Ratjika Chanamai and David McClements, Dependence of creaming and rheology of monodisperse oil-in-water emulsions on droplet size and concentration, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 172 (1-3) (2000) pp.79-86

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11. T. Kawakatsu et al., The effect of the hydrophobicity of microchannels and components in water and oil phases on droplet formation in microchannel water-in-oil emulsification, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 179 (1) (2001) pp.29-37

12. U.S. Patent and Trademark Office, United States Patent: Epstein - 6,017,548, January 25, 2000

13. U.S. Patent and Trademark Office, United States Patent: Estrin, October 31, 2000

14. U.S. Patent and Trademark Office, United States Patent: Flom, June 17, 1986

15. Vona Jr., S. A.; Friberg, S. E.; Brin, A.; Location of fragrance molecules within lamellar liquid crystals, Colloids and Surfaces A: Physicochemical and Engineering Aspects, Volume 137, Issues 1-3, 15 June 1998, Pages 79-89

16. Noveon, The Specialty Chemicals Innovator, Skin Care Products Formulated with Pemulen® Polymeric Emulsifiers, http://www.pharma.noveoninc.com/literature/tds/tds117.pdf

17. Howard R. Moskowitz, David Fishken, Rheological characteristics and consumer acceptance of emulsion products, Cosmetics and Toiletries, vol.93, 1978, 31

18. J.A.Rogers, Means for controlling the rheological behavior of emulsions, Cosmetics and Toiletries, vol.93, 1978, 49

19. Lihang Quan, Haohao Huang, Eli Ruckenstein, Self-compatibilization of polymer blends prepared via functionalized concentrated emulsion polymerization, Journal of Polymer Science, Part A, Polymer Chemistry, vol.23, 1999,3244

20. Robert Bornfriend, Effect of processing on the rheological behavior of emulsions, Cosmetics and Toiletries, vol.93, 1978, 61

21. Merck Index, 13th Edition, Merck & Co., Inc., Whitehouse Station, NJ 2001.

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