Chapter 5

Applications of Microemulsions

5.1 Literature Survey

The unique properties of microemulsions make them interesting for commercial

applications and technical processes. In particular, the high solubilizing power

of microemulsions and microemulsion systems for organic and inorganic com-

pounds favors their use as solvents for a large number of applications. However,

cost arguments and the complex behaviour of multicomponent systems form-

ing microemulsion phases have been obstacles to large-scale applications in the

past. But the increasing number of patents beginning in the 1990s now shows

that many problems could be solved with systematic studies on the structure

[Kahlweit et al. , 1987] and the phase behaviour of microemulsions [Kahlweit

et al. , 1989a; Kahlweit et al. , 1989b]. Increasing knowledge of multiphase

systems comprising microemulsion phases led to tailor-made microemulsions,

e.g. with enhanced temperature stability, low surfactant content [Jakobs et al.

, 1999] and diverse polar oils from natural [Alander and Warnheim, 1989b;

Alander and Warnheim, 1989a; Monig et al. , 1996] or petrochemical sources

[Li et al. , 1999].

O/W-droplet microemulsions are widespread in cleaners cosmetics and per-

sonal care products.They can also be used as media for enzymatic reactions.

W/O-droplet microemulsions can be found in fuels, but also in more sensitive

products like cosmetics and food .

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5.1.1 Microemulsions in Cosmetics

The properties of microemulsions make them attractive for cosmetic formula-

tions from several points of view. First, the transparent appearance gives a

perception of a "clean" system, for a large majority of potential customers this

is an essential property. The small droplet size and the transparency make

them look like solutions, but the fact that they contain colloidal size droplets

of oil in water, or vice versa, signi�cantly enhances their use in cosmetics.

Because of the droplets, microemulsions possess the properties of both wa-

ter and oil, in contrast with a solution, the properties of which are intermediate

between those of oil and water. The consequence is of decisive importance for

the formulator. Where both water-soluble compounds such as salts and oil-

soluble additives can be freely combined into one transparent liquid.

This advantage from the formulation point of view is further enhanced

by the fact that microemulsions are thermodynamically stable. No problems

are encountered with changes during long-term storage, the shelf life from

the nonchemical aspect is in principle in�nite, limited only by the chemical

stability of the components.

Finally, the microemulsions form spontaneously, and only mild stirring is

necessary to bring about the �nal state more rapidly. The savings compared

to the investment for emulsion production with expensive intensive-mixing

equipment usually may compensates for the increase in cost for the higher

concentrations of surfactants and cosurfactants. These reach combined con-

centrations of 10-15% by weight, about four times that needed for an emulsion,

increasing the cost per pound of the product. However, it should be borne in

mind that the surfactant-cosurfactant compounds allowed in cosmetics often

are chosen for their bene�cial e�ects, thus alleviating the negative economic

aspects. [Aikens and Friberg, 1999].

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5.1.2 Microemulsions in Hair Care

Microemulsions have also been utilized for hair care products. Holloran and

Hoag report on a microemulsion product with modi�ed silicone oils and cationic

surfactants. This product exhibits good long-term stability, high clarity, and

shows a very good performance on the combability of treated hair [Halloran

and Hoag, 1998]. Ostergaard et al. developed microemulsions with a quater-

nised silicone oil for hair care products [Ostergaard et al. , 2004]. This product

improves the colour retention and the combability of hair conditioners. More-

over, clear hair conditioning formulations, which remain clear on dilution and

are highly freeze stable, can be prepared from microemulsions. [von Rybinski

et al. , n.d.].

5.1.2.1 Hair

Hair care involves care and stimulation of scalp tissue and its appendages and

protection and care of the hair shaft as it passes beyond the surface of the skin.

The latter is the subject of cosmetic preparations, which should acquire one

or more of the following functions: (1) Hair conditioning for ease of combing.

This could also include formulations that can easily manage styling by combing

and brushing and the hair's capacity to stay in place for a while. The di�culty

in managing hair is due to the static electric charge, which may be eliminated

by hair conditioning. (2) Hair ``body'', i.e. the apparent volume of a hair

assembly judged by sensory measurements which involves sight and touch.

Hair is complex multicomponent �ber with both hydrophilic and hydropho-

bic properties. It consists of 65�95% by weight of protein and up to 32% water,

lipids, pigments and trace elements. The proteins are made of structured hard

α-keratin embedded in an amorphous, proteinaceous matrix. Human hair is a

modi�ed epidermal structure, originating from small sacs called follicles that

are located at the border line of dermis and hypodermis. A cross section of

human hair shows three morphological regions, the medulla (inner core), the

cortex that consists of �brous proteins (α-keratin and amorphous protein),

and an outer layer namely the cuticle. The major constituents of the cortex

and cuticle of hair are protein or polypeptides (with several amino acid units).

Keratin has an α-helix structure (molecular weight in the region of 40 000�70

000 Da, i.e. 363�636 amino acid units).

The isoelectric point (i.e.p.) of hair keratin (i.e. the pH at which there is

an equal number of positive, -NH+ and negative, -COO− groups) is ∼pH 6.0.

However, for unaltered hair, the i.e.p. is at pH 3.67. The above charges on

human hair play an important role in the reaction of hair to cosmetic ingre-

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dients in a hair care formulation. Electrostatic interaction between anionic or

cationic surfactants in any hair-care formulation will occur with these charged

groups.

The above charges on human hair play an important role in the reaction of

hair to cosmetic ingredients in a hair care formulation. Electrostatic interaction

between anionic or cationic surfactants in any hair care formulation will occur

with these charged groups. Another important factor in the application of hair

care products is the water content of the hair, which depends on the relative

humidity (RH). At low RH (< 25%), water is strongly bound to hydrophilic

sites by hydrogen bonds (sometimes this is referred to as ``immobile'' water).

At high RH (> 80%), the binding energy for water molecules is lower because

of the multimolecular water�water interactions (this is sometimes referred to as

``mobile'' or ``free'' water). With increasing RH, the hair swells; on increasing

relative humidity from 0 to 100% the hair diameter increases by ∼14%. When

water-soaked hair is put into a certain shape while drying, it will temporarily

retain its shape. However, any change in RH may lead to the loss of setting.

[Tadros, 2005b].

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5.2 Conditioning Hair Oil - Microemulsion

Microemulsions due to their properties like high clarity, spontaneity and ease

of formation along with long-term stability, makes them more desirable for

personal care applications. Microemulsi�cation of a widely used substance like

coconut oil for its known conditioning bene�ts, along with an active agent

like conventional conditioning agent e.g, a quaternary ammonium halide can

enhance the existing conditioning properties of the oil. The conditioning prop-

erties on hair, that could be derived from the microemulsion of coconut oil

along with an additional conditioning agent would be comparatively better

than individual components alone. Thus, with the aim of achieving additional

bene�ts through the combination of nonpolar coconut oil and quaternary am-

monium halide, conditioning hair oil microemulsion was formulated with the

assistance of a nonionic surfactant and water. The following components were

used for the formulation.

Coconut Oil

Historically, coconut has been used as a hair dressing the developing oil in

countries in the tropical regions of the globe where the coconut is cultivated

extensively. Because the low molecular weight of coconut oil, it penetrates

cortex, whereas bulkier molecules like mineral oil or some bulky triglycerides

does penetrate hair at all [Rele and Mohile, 1999]. Prolonged use of coconut

has been known to lead to healthy looking long hair, suggesting oil that it

may prevent damage to the cuticle in grooming procedures involving abrasion.

Obvious the lubricating is e�ect of oil on �ber friction,which reduces abrasive

damage, especially combing.

Conditioning Agent

Conditioning are added to keep the hair cuticle smooth and slippery. These

compounds deposit on the surface of the hair and improve its sensory proper-

ties like feel, softness, and compatibility, while reducing static charge. Cationic

surfactants in low levels can improve wet and dry combing properties of hair.

Cationics such as long chain quaternary ammonium compounds acts like a

antistatic agent reducing inter�ber or �ber-comb friction, resulting their ap-

plication as hair conditioner. e.g, didodecyldimethylammonium bromide

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Nonionic Surfactant

Nonionic surfactants like alcohol ethoxylates(uncharged molecules) are gener-

ally mild in nature and show little foaming . Their low toxicity, low sensiti-

zation and low eye irritation make them ideal for solubilization of fragrances

and otherwise insoluble additives for hair conditioning. Also, the absence

of ingredients that can damage the hair is an added advantage [Louis and

Nardello-Rataj, 2008].

Silicones

Silicones can be very e�ective as conditioning agents. These include the high-

molecular weight polydimethyl siloxanes or trimethicones, which makes the

hair shiny/ glossy, soft and more manageable.

5.3 Materials

5.3.1 Triglyceride - Coconut Oil

Re�ned Coconut Oil (RCNO) which was used for all experimental purposes

was procured from by M/S Marico Industries, India. The Acid Value for the

coconut oil used was in the range of 0.0 to 0.1 mg KOH/ g of oil, Saponi�cation

Value approximately 250 mg KOH/ g of oil and Iodine Value between 8 to 10

mg I2 / g of oil. The composition of the coconut oil is as shown in Table.

5.3.2 Conditioning Agent

Quaternary Ammonium Halide, Didodecyldimethylammonium bromide (DDAB)

(structure) of 99.99 % purity, was obtained from Acros Organics U.S.A. The

quaternary compound was used as received

5.3.3 Surfactant

Non ionic surfactant of the type (CiEj), n-dodecyl heptaoxyethylene glycol

monoether with the chemical formula C12H25(OCH2CH2O)7OH, abbreviated

C12E7, was gifted by M/S Galaxy Surfactants, India. These are generally pro-

duced by ethoxylation of a fatty chain alcohol (here dodecanol). The starting

alcohol generally has a distribution of alkyl chain lengths and the resulting

ethoxylate has a distribution of ethylene oxide chain lengths. Thus the ethy-

lene glycol numbers mentioned refers to average numbers. The surfactant was

used as received.

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5.3.4 Cosurfactant

Phenyl Carbitol (PC) (C6H5CH(OCH2CH2)2OH), was used as cosurfactant.

PC was obtained from M/S Galaxy Surfactants, India. The cosurfactant was

used as received.

5.3.5 Silicones

Phenyl Trimethicone (DC 556), which is a cosmetic grade �uid was obtained

from Dow Corning Ltd.

5.4 Methods

5.4.1 Formulation and Composition of Microemulsion

The methodology for formulation and identi�cation of microemulsion is sim-

ilar to that mentioned in chapter four Section 4.2.4 and 4.2.5. It must be

noted that, the mixture of DDAB + Coconut Oil + Nonionic Surfactant +

Cosurfactant turned into a clear monophasic, isotropic microemulsion only af-

ter addition of water. Prior which the showed characteristics of a biphasic,

anisotropic mixture.

Many microemulsions were formulated keeping in mind the purpose of Hair

Conditioning. The microemulsions with the composition given in Table. 5.1,

agreed most with the conditions of safety, ease of handling and aesthetics

associated with personal care formulations.

Table 5.1: Composition of Conditioning Hair Oil Microemulsions

No DDABWt.%

CoconutOil

C12E7

Wt.%PhenylCarbitolWt.%

SiliconeDC 556Wt.%

H2OWt.%

Appearance

1 - 100 - - - - Clear2 1 92.6 5 1 - 0.4 Clear3 1 87.6 5 1 5 0.4 Clear

The e�ectivity and e�ciency of these samples, as Hair Conditioning agents

was further investigated.

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5.4.2 Stability Study

The stability of the above mentioned samples was tested to assess the changes

in their composition and appearance, with changing temperature. The long

term stability at ambient temperatures, which in�uences their shelf life was

also studied.

5.4.2.1 Temperature Variation

During the transportation of cosmetic products, it is very common to encounter

freeze (e.g. store at low temperature on plane or vehicle) and thaw (e.g. being

idled to ambient temperature before custom checking) cycle. If products can-

not tolerate a certain degree of change of temperature, it may cause signi�cant

losses. Layer separation may be formed in liquid based products which may

a�ect its proper functioning.

Thus, the microemulsion (hair oil) samples were subjected to contrast tem-

peratures. The microemulsion samples were maintained at 50 °C and 10 °C

(The microemulsions are of w/o nature solidi�es at this temperature) for 24

hours. It was observed that the sample shows slight translucency at higher

temperatures, but when bought at ambient room temperatures (25 °C) it gains

back its isotropic, monophasic form on slight shaking. When the microemul-

sion (solidi�ed) samples at 10 °C are allowed to thaw at room temperatures,

they again resume isotropic, monophasic form on slight shaking.

5.4.2.2 Real Time

Microemulsions are thermodynamically stable with appearance and properties

that signi�cantly in�uences its �nal application. But, depending on chemical

nature of its components, its stability and other properties would certainly

change. Thus, it is of considerable importance to ascertain its stability for

longer duration, which would heavily weigh upon its shelf life.

The microemulsion (hair oil) samples were maintained undisturbed at room

temperature conditions. It was observed that the microemulsion samples re-

tained their characteristics and remained stable for 18 months. After which

they showed slight turbidity. Incidentally coconut oil has shelf life of 18 months.

5.4.3 Application of Microemulsion on Hair Tresses

The conditioning bene�ts of the above mentioned microemulsion samples were

investigated against plain coconut oil (used as a control). Samples (tresses) of

straight, curly hair of Indian origin were used in this work. The length of the

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Indian hair strands was 25 cm. The microemulsion samples and the control

were applied on hair tresses and were further washed to study their e�ect post

washing, the protocol followed is mentioned below.

Oiling Cycles

1. The hair tresses were bundled to weigh 3.5 -4.0 gm each and were

fastened with rubber band at one end, for easy handling.

2. Oil was applied on the weighed tress (0.4ml for 4gm hair tress). The

tress was allowed to stand for 30 minutes.

3. The hair tress was washed using 0.4 ml of 15 % SLES (Ten strokes were

applied during washing).

4. The hair tress was rinsed under running tap water till strand was free

of SLES solution.

5. The tress was dried using a hair drier at ambient temperature.

6. Steps 2 to 5 were repeated for 20 times.

7. The protocol was performed in �ve sets.

5.4.4 Sensory Evaluation of Hair - Post Application

The conditioning hair oil formulations, were applied on hair tresses following

the protocol mentioned previously. The treated hair tresses were evaluated on

the basis of their visual and tactile di�erences.

The treated hair tresses were judged by a professional, trained panel of

seven experts from Hair-Care R&D Unit of Marico Ind. Ltd (Mumbai, India).

On the basis tactile and visual variations in parameters like Softness, Smooth-

ness, Shine, Ease of Combing and Frizziness, the e�ectivity and e�ciency of

the conditioning hair oil microemulsions was ascertained on the scale of 0 to

5. Where 5 denotes the best performance by the product under investigation

for any particular parameter.

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5.5 Results and Discussion

The Conditioning Hair Oil microemulsion samples were compared for their

e�ect on hair tresses against re�ned coconut oil (RCNO). The di�erence be-

tween in performance of microemulsions and RCNO on hair was assessed, on

the basis of the visual and tactile changes on hair tresses. The parameters on

which the performance was compared were Softness, Smoothness, Shine, Ease

of Combing and Frizziness.

5.5.1 Softness

The change in softness of Hair tresses was ascertained on the basis of the tactile

changes, resultant of the application of RCNO against Conditioning Hair Oil

Microemulsions. It was observed that microemulsion with 1% DDAB fared

slightly better than RCNO, where as signi�cantly better softness was felt on

hair tresses by application of microemulsion with 1% DDAB and silicon DC

556 in comparison with RCNO as shown in Fig. 5.1.

Figure 5.1: Comparison of Softness on Hair Tresses by RCNO, Microemulsionwith 1% DDAB and Microemulsion with 1% DDAB + DC 556

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5.5.2 Smoothness

The change in smoothness of Hair tresses was ascertained on the basis of the

tactile changes, resultant of the application of RCNO against Conditioning

Hair Oil Microemulsions. It was observed that microemulsion with 1% DDAB

shows smoothness which is faintly better than plain RCNO. Microemulsion

with silicone showed better smoothness on hair tresses in comparison with

RCNO as depicted in Fig. 5.2.

Figure 5.2: Comparison of Smoothness on Hair Tresses by RCNO, Microemul-sion with 1% DDAB and Microemulsion with 1% DDAB + DC 556

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5.5.3 Shine

The change in shine of Hair tresses was ascertained on the basis of the visual

changes, resultant of the application of RCNO against Conditioning Hair Oil

Microemulsions. It was observed that microemulsion with 1% DDAB showed

distinctively better shine as compared to both plain RCNO and microemulsion

with silicone as shown in Fig. 5.3.

Figure 5.3: Comparison of Shine on Hair Tresses by RCNO, Microemulsionwith 1% DDAB and Microemulsion with 1% DDAB + DC 556

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5.5.4 Ease of Combing

Ease of combing or combability is an important attribute in hair conditioning,

and refers to the ease or di�culty in combing of hair [Velasco et al. , 2009,].

It depends on the forces which are opposite to the action of combing hair.

The ease of combing for hair tresses was ascertained after the application of

RCNO against Conditioning Hair Oil Microemulsions. It was observed that

microemulsion with 1% DDAB fared signi�cantly better at ease of combing

than plain RCNO and microemulsion with silicone DC 556 as shown in Fig.

5.4.

Figure 5.4: Comparison of Ease of Combing on Hair Tresses by RCNO, Mi-croemulsion with 1% DDAB and Microemulsion with 1% DDAB + DC 556

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5.5.5 Frizziness

The microemulsion samples were also examined for their e�ect on tackling

frizziness. It was observed that, microemulsion with silicone fared slightly

better than microemulsion with 1% DDAB and plain RCNO as shown in Fig.

5.5. Also, microemulsion with 1% DDAB proved to be slightly better than

plain RCNO for tackling frizziness.

Figure 5.5: Comparison of Frizziness on Hair Tresses by RCNO, Microemulsionwith 1% DDAB and Microemulsion with 1% DDAB + DC 556

Thus, the sensory evaluation by the expert trained panel for the condi-

tioning hair oil microemulsion samples against plain RCNO indicate that, mi-

croemulsion samples with 1% DDAB fares better and provides better condi-

tioning bene�ts on hair tresses than plain RCNO. The conditioning hair oil

microemulsion fared better on almost all aspects of assessment. Also, the

conditioning properties of microemulsion like softness and smoothness were

enhanced and augmented by silicone DC 556 (Phenyl Trimethicone)

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