2012_savary et al._impact of emollients on the spreading properties of cosmetic products a combined...
TRANSCRIPT
-
8/13/2019 2012_Savary Et Al._impact of Emollients on the Spreading Properties of Cosmetic Products a Combined Sensory a
1/8
Colloids and Surfaces B: Biointerfaces 102 (2013) 371378
Contents lists available at SciVerse ScienceDirect
Colloids and Surfaces B: Biointerfaces
journal homepage: www.elsevier .com/ locate /colsur fb
Impact ofemollients on the spreading properties ofcosmetic products:A combined sensory and instrumental characterization
Graldine Savary, Michel Grisel, Cline Picard
Universit duHavre, URCOM, EA 3221, FRCNRS3038, 25 rue Philippe Lebon, B.P. 540, 76058 LeHavre cedex, France
a r t i c l e i n f o
Article history:
Received 15 March 2012
Received in revised form 19 June 2012Accepted 19 July 2012
Available online 9 August 2012
Keywords:
Spreading
Cosmetic emulsions
Sensory evaluation
Contact angle
Texture analysis
Correlation
a b s t r a c t
This study deals with the impact ofemollients on the spreading properties ofcosmetic products using a
combined sensory-instrumental approach. To that purpose, three esters and one silicone were selected
and incorporated separately into an oil phase. Different cosmetic o/w emulsions were then prepared
with these different oil phases. Both of them were analyzed by instrumental techniques and in vivo
sensory analyses. A significant effect of the emollient used was established in emulsions and in oil
phases as well. Concerning emulsions, results reveal a clear correlation between in vivo spreading
evaluation and friction coefficient parameters measured by texture analyzer, despite a fairly low cor-
relation coefficient (Pearson coefficient =0.78). Concerning oil phases, characterization of spreading
was done by monitoring the contact angle relaxation of a drop of solution after deposition on a flat
PMMA surface whereas sensory procedure was based on spontaneous spreading ofoil phases onto the
skin. Finally, good correlations between in vivo sensory analysis and instrumental measurements ofboth
oils and emulsions were found, thus promising the possible development ofpredictive tools to evaluate
spreadability.
2012 Elsevier B.V. All rights reserved.
1. Introduction
Sensory properties in skin care formulations mainly result from
ingredients such as emollients, rheology modifiers, emulsifiers and
humectants. Generallyspeaking, emollients, usedat levels between
3 and 20% (w/w)in emulsions, representthe second major ingredi-
ent after water [1]. Emollients can be of varied chemical structures
including esters and silicones. When incorporated in cosmetic
emulsions, esters and silicones are hydrophobic ingredients that
compose part of the oil phase. Despite their dubious reputation,
cyclic siliconesare widely found in skin care products fortheir spe-
cific properties when compared to the other emollients [2]. Esters
belong to a large family of compounds used either as emollient
or as emulsifier in cosmetic emulsions and can be used to replace
silicones [3]. Related to their physico-chemicalproperties, skin-feeleffects of theseemollients arecomplexand can be perceivedduring
and/or afterapplication on skin:gliding, sliding, moisturizing, plas-
ticizing, protecting, conditioning, softening, smoothing, etc. [1,4,5].
Concerning the properties during application on the skin, emol-
lients decrease the friction coefficient due to their lubricant prop-
erties and modify the spreading performance of the product [6].
Corresponding author. Tel.: +33 232 744394; fax: +33 232 744391.
E-mail address: [email protected](C. Picard).
To achieve adequate efficacy and user acceptance of a cos-
metic emulsion, spreading is an important property. Descriptive
sensory analysis of skin care products usually includes attributes
such as difficulty of spreading or slipperiness that are evalu-
ated during application of either pure ingredients [7] or creams
and lotions [8,9]. For example, Parente et al. [2] characterized
eight liquid emollients including esters and silicones (i.e. decyl
oleate, isopropyl myristate, dimethicone, cyclomethicone) for both
attributes. Authors compared properties of emollients alone but
they did not study their characteristics when included in cosmetic
emulsions.
However, sensory analyses are time-consuming and require an
available and well-trained panel of assessors. Therefore, different
studies were done inorderto establisha relationshipbetweentext-
ural attributes and structural or physical characteristics [1012].In the field of food sciences, many studies have been carried out
to develop an instrumental approach especially using texture pro-
file analysis [1315]. However, nowadays the number of studies
on spreading performed in the cosmetic domain remains limited.
Kusakari et al. [16] developed a measuring device to evaluate the
frictional force as an indicator of the spreading resistance whereas
DiMuzio et al. [17] established a correlation between spreadability
and rheological parameters obtained from stress sweep and creep
tests on o/w emulsions.
The first goal of the present study was to test the poten-
tial development of texture analysis to evaluate the spreading
0927-7765/$ seefrontmatter 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.colsurfb.2012.07.028
http://localhost/var/www/apps/conversion/tmp/scratch_6/dx.doi.org/10.1016/j.colsurfb.2012.07.028http://localhost/var/www/apps/conversion/tmp/scratch_6/dx.doi.org/10.1016/j.colsurfb.2012.07.028http://www.sciencedirect.com/science/journal/09277765http://www.elsevier.com/locate/colsurfbmailto:[email protected]://localhost/var/www/apps/conversion/tmp/scratch_6/dx.doi.org/10.1016/j.colsurfb.2012.07.028http://localhost/var/www/apps/conversion/tmp/scratch_6/dx.doi.org/10.1016/j.colsurfb.2012.07.028mailto:[email protected]://www.elsevier.com/locate/colsurfbhttp://www.sciencedirect.com/science/journal/09277765http://localhost/var/www/apps/conversion/tmp/scratch_6/dx.doi.org/10.1016/j.colsurfb.2012.07.028 -
8/13/2019 2012_Savary Et Al._impact of Emollients on the Spreading Properties of Cosmetic Products a Combined Sensory a
2/8
372 G. Savary et al. / Colloids and Surfaces B: Biointerfaces 102 (2013) 371378
properties of cosmetic emulsions. The second target of this study
was to establish an instrumental measurement to characterize the
spreadingattributes of the various oil phases used to formulate the
o/w emulsions.
In their study, Gorcea and Laura [1] assessed the physicochemi-
cal properties of four cosmetic emollient esters in vitro to correlate
with in vivo sensory attributes. Spreading properties were charac-
terized by spreadingvalues on Vitro-Skin, surface tension,contact
angle and viscosity measurements. Indeed, surface wetting and
absorption dynamics are two key phenomena that govern the
spreading of a fluid on a given surface [18].
Wettability phenomena can be evaluated by studying the con-
tact angle formed at the air/solid/liquid contact point when a drop
of liquid is deposited on the solid surface [19]. When a liquid drop
is placedin contact with a flat, horizontal substrate, capillary forces
drive the interface spontaneouslytowards equilibrium. As the drop
spreads, the contact angle changes from its initial maximum value
at the very first instant of contact, towards its final equilibrium
angle 0 in the case of partial wetting, or 0 if the liquid com-
pletely spreads and wets the solid. The results more or less fit a
master curve showing relationships between contact angle versus
time [20]. Several parameters affect wettability [1922]: chemical
characteristics of the liquid and substrate, roughness and hetero-
geneity of the solid, viscosity, surface tension, density and volumeof the drop of the liquid and its potential evaporation.
In the present study, three esters and one silicone ingredients
chosen as major emollients used in the cosmetic industry were
studied as components of the oil phase of the given emulsions. The
impact of emollients on the spreading properties of the oil phases
and of the o/w emulsions formulated with these oil mixtures was
studied by a combined sensory-instrumental approach.
Spreading of emulsions was first investigated by in vivo tests
and in vitro methods including texture analysis. Then spreading
and penetration of the oil phases were characterized using sensory
evaluations and contact angle measurements. Results were then
analyzed and compared, and a correlation matrix was drawn up to
establish the relationships between both sensory and instrumental
measurements.
2. Material and methods
2.1. Preparation of the emulsions
Table 1 reports the name and physico-chemical properties of
the cosmetic grade esters and the silicone selected for this study.
Esters 1 and 2 are ester or diester from penta- or dipenta-
erythrityl alcohol respectively. Theyexhibita star-shaped structure
and a relatively high molar mass, so they are generally selected for
the consistency and texture they bring to the formulations. Ester 3
is a linear ester with a low molar mass. It exhibits properties very
close to those of silicone: improvement of spreading on skin, silkyafter-feel sensation on skin. Silicone belongs to the so-called group
of cyclic volatile dimethylsiloxanes or cyclomethicones. It is well-
known in cosmetics for producing a silky after-feel sensation and
improvingspreading on skin. Esters 1, 2 and3 were kindlygivenby
Starinerie Dubois (France) and silicone was obtained from Evonik
Goldschmidt (Germany).
A standard emulsion and four test emulsions were prepared by
varying the composition of the oil phase in order to analyze the
effectof each emollient by itself (Table 2). Ingredients were chosen
in order to respect two main criteria:
1. Those that produce a stable emulsion close to an industrial cos-
metic one in terms of complexity and number of ingredients
2. Those whose oil phase is a good solvent to solubilize the differ-
ent emollients chosen. Thus, at room temperature, a liquid oil
phase with or without emollient is obtained, making it easier to
characterize.
Forthe standardemulsion(200g),the oilphase (A) was firstpre-
pared by mixing the ingredients as listed in Table 2 and by heating
the mixture to 75C under stirring. In the meantime, the aque-
ous phase (B) was prepared using purified water (type 1). The mix
of water and glycerine was slowly sprinkled with carbomer pow-
der and left 20min without stirring. Then the aqueous phase was
heatedto 75 C.When bothphases were at75 C,the water loss due
to evaporation was compensated by adding water to the aqueous
phaseand theoilphasewas thengently addedto PhaseB understir-
ringfor 3 min with a D7801 homogenizer (Ystral GMBH, Germany).
Theemulsionwas then continuouslystirred at300 rpmusing a Tur-
botest motor generator with a 65mm turbine (VMI, France) until it
cooleddownto 50 C. Sufficient amountof 1 M aqueous NaOH solu-
tion (CarloErba, Italy) was then added to yield a final pH between
6.2 and 6.5 in the preparation. The stirring rate was then increased
to 500 rpm. Finally, the preservative (Phase C) was added at 40C
and the emulsion was kept under stirring for an additional period
of 5min until its temperature dropped to ambient temperature.
For the test emulsions with ester, the preparation was exactlythe same except for the composition of the oil phase (Table 2).
For the test emulsion with silicone, the emollient was added
with the preservative at 40 C in order to avoid its evaporation.
Samples were stored at 4 C during three months at the most.
2.2. Instrumental spreading characterization
2.2.1. Contact angle measurements
Spreading of emollients solubilized in the oil phase was inves-
tigated by the sessile drop method (Digidrop GBX goniometer). To
this purpose, a drop of product is formedat theendof a syringe until
it gently falls under its own weight on the solid support, and then
spreads onto it. A high speed camera (25 images/s) recorded the
evolution of the contact angle just after deposition and during theentire spreadingprocess. The solid support chosen for these exper-
iments was polymethyl methacrylate (PMMA) plates (Helioplate
HD2, Helioscreen, France). This support is commonly used in cos-
metics for the in vitro determination of SPF and offers several
advantages for our concerns, as compared to artificial skin: it is
less expensive, easier to handle in terms of surface preparation and
cleaning,it is reproducible in termsof surface chemistryand rough-
ness and it is reusable. For each ingredient, both the right and the
left contact angles were measured using the Windrop++ software,
and the corresponding average contact angle was followed over a
period of timeuntil stabilization. The final results correspond to the
mean of three reproducible kinetic experiments. All measurements
were realized at room temperature.
2.2.2. Texture analysis
Spreading of cosmetic creams was measured on a TA.XT
plus Texture Analyzer (Stable Microsystems, United Kingdom),
equipped with the A/FR Friction rig module at room temperature.
The principle of the test consists in displacing at a constant speed
of 3 mm s1 a PMMA plate (Helioplate HD6) surmounted by a
square weight (207.9g, 6.2cm length), on a static plate covered
with a polypropylene sheet. Prior to experiment, using a pipette
designed for creamy products (Microman, Gilson, France),4 drops
of cream of 40L each were deposited on the under-side of the
weight in order to design a 22 cm2. The force required to move
the weight over a length of 6 cm was monitored over time. Textu-
ral data related to friction andspreading of creams were calculated
from a graph obtained during experiments (Fig. 1). The positive
-
8/13/2019 2012_Savary Et Al._impact of Emollients on the Spreading Properties of Cosmetic Products a Combined Sensory a
3/8
G. Savary et al. / Colloids and Surfaces B: Biointerfaces 102 (2013) 371378 373
Table 1
Names and physico-chemical properties of the emollients used.
Code INCI name Structure Mw logPa
Ester 1 Pentaerythrityltetraethylhex-
anoate
640.9 11.3
Ester 2 Dipentaerythrityl
pentaisononanoate
(content > 97%) 949.0 12.0
Ester 3 Propanediol
dicaprylate
328.5 6.4
Silic one Cyclopentasiloxane,
cyclohexasiloxane
(content > 95%) 370.8 5.2
a logPvalues were obtained or calculated from http://pubchem.ncbi.nlm.nih.gov.
area between 0 and 14s was determined for each cream and the
mean value of 3 reproducible experiments was reported and con-
sidered as an instrumental parameter characterizing the spreading
of creams (TEM).
2.2.3. Physico-chemical characterization of ingredients, oil
phases and creams
Density of pure ingredients and oil phases containing one
ingredient was characterized with a portable densimeter (Mettler
Toledo, France).
Surface tension of pure ingredients and ingredients in the oil
phase was determined by the pendant drop method (Digidrop GBX
goniometer). Surface tension value was the mean value obtained
when measuring ten drops of the same volume. Both measure-
ments were done at room temperature.
Rheological properties in flow mode of pure ingredients, oil
phases and creams were measured on a AR 2000 rheometer
(TA Instruments, USA) at 25C. Cone-and-plate measuring sys-
tem geometries were used for these characterizations, and chosen
depending on the viscosity range, respectively: 60mm diameter
aluminium coneplate with an angle of 01957, 60mm diameter
Table 2
Composition of thestandard and test emulsions.
Phase Ingredients (INCI name) Suppliers Weight (%, w/w)
Standard emulsion Test emulsions
A Coco caprylate/caprate Starinerie Dubois (France) 14 8
Isohexadecane Croda (England) 8 3
Cetyl alcohol (and) glyceryl stearate (and) PEG-75
(and) ceteth-20 (and) steareth-20
Starinerie Dubois (France) 5 5
Emollient See Table 1 0 11
B Aqua 61.7 61.7
Glycerine CarloErba (Italy) 5 5
Carbomer Lubrizol (Belgium) 0.3 0.3
C Pr opylen e glycol (and) me th ylpr opan edio l( and)
potassium sorbate (and) methylisothiazolinone
Biophil (Italy) 1 1
http://pubchem.ncbi.nlm.nih.gov/http://pubchem.ncbi.nlm.nih.gov/ -
8/13/2019 2012_Savary Et Al._impact of Emollients on the Spreading Properties of Cosmetic Products a Combined Sensory a
4/8
374 G. Savary et al. / Colloids and Surfaces B: Biointerfaces 102 (2013) 371378
0
5
10
15
20
25
30
35
0 2 4 6 8 10 12 14
F
orce
(g)
Time (s)
Fig. 1. Texture profile obtained with the standard emulsion.
acrylic coneplate with an angle of 20153 and 40mm diameter
steel coneplate with an angle of 059. Flow curves were recorded
with a continuous ramp test in shear rate (0.0117,000s1) during
5min. Viscosity values for pure ingredients and oil phases (VOP)
were selected in the Newtonian region, while for the cosmetic
emulsions, viscosity values (VEM) at a shear rate of 1000s1 were
chosen.
2.3. Sensory analyses
Sensory analyses were carried out to evaluate spreading of the
five emulsions (SEM) on the one hand, and spreading and penetra-
tion of the five corresponding oil phases (SOPand POPrespectively)
on the other hand. Each of these three attributes was evaluated
separately. The sensory panel consisted of ten female volunteers
from 20 to 40 years old. The assessors were trained in two train-
ing sessions followed by two test sessions in which samples wereevaluated twice. Samples were labelled with three-digit random
numbers and were randomly presented at room temperature in
5 mLopaque vials. Sensory attributes were assessed on the inter-
nal side of the forearm according to well-defined procedures as
described below. Tests were carried out successively on the left
and rightarms.Prior toand between each sampletest,theassessors
cleaned the skin of theirforearm with skin cleanser, then waterand
finally dried it carefully. Testing took place at the sensory facilities
of theUniversityof Le Havre,France. Analysis conditions were con-
trolled before sessions, in particular the lighting in sensory booths.
Because ingredients and emulsions possess quite different
physicochemical properties, three different evaluation procedures
were defined, all with strict protocols as described below.
2.3.1. Evaluation of spreading for emulsions
Spreadability was defined as the ease of moving the cosmetic
emulsion over a given distance. The distance defined on the skin
was of 6c m. The assessor put down 50L of the sample at 6 cm
from the arm bend with a M250 positive displacement pipette
(Microman, Gilson, France). With the index finger, the sample is
spread only once towards the hand for a fixed distance of 6cm.
The assessor evaluated the force while applying the sample onto
the skin surface and indicated the score for each sample on a scale
from 0 to 9 with0.5 increments and verbal anchor points. To quan-
tify this attribute, assessors were trained to theresponsescalewith
internal referent samples (scores 1 and8). Duringthe test sessions,
assessors were authorized to re-test either samples or references
several times.
2.3.2. Evaluation of spreading for oil phases
Spreading of the oil phases was defined as the surface of skin
covered by the sample in one minute [23]. The larger the covered
surface, the easier the sample spreads. The assessors were asked to
put down 10L (10L syringe, SGE, Australia) of sample at 6 cm
from the arm bend and to keep the forearm horizontal, without
moving, for one minute. According to the anatomy of assessors
forearms,circular or ellipsoidal formswere coveredby the oils.Out-
lines of theform covered by thespread substance were then drawn
with a pen for skin and the lengths of the semi-major and semi-
minor axes of the ellipse were measured. The spreading of each oil
phase was then calculated according to the following equation:
SOP = a b
VS tS
where a and b are the lengths of the semi-major and semi-minor
axes respectively (in mm), VS is the volume of sample (in L) and
tS, the time (in min).
2.3.3. Evaluation of the oil phase penetration
Penetration of the oil phases was defined as the time necessary
to observe the total disappearance of the sample put down on skin.
0.5L of sample was put down at 6c m from the arm bend. Theassessor started the chronometer and kept her forearm still under
lighting. The assessor was asked to observe the deposit and indi-
cated when she could not observe the product any more on the
skin as theconsequence of its absorption into the skin. The time for
total penetration was recorded and the penetration rate was then
calculated according to the equation:
POP =tP
VP
where tPis the time for penetration (in min) and VP, the volume of
sample (inL).
2.4. Data analysis
Analyses of variance (ANOVA) were conducted to check dif-
ferences between properties of each emollient. One-way ANOVAs
were performed on each instrumental measurement and two-way
ANOVAs were computed on each sensory attribute with samples
and assessors as variables. In case of significant difference at 95%,
Tukeys HSDpost hoccomparisons were then carried out to inves-
tigate the sample effect.
The correlation matrix of the mean values was used in order
to establish and interpret the relationship between sensory and
instrumental measurements.
All mathematical and statistical analyses were performed using
XLSTAT software.
3. Results and discussion
3.1. Sensory spreading of emulsions
Spreading of a cosmetic cream is a determinant textural
attribute that governs the performances of the product during its
application on the skin. In order to evaluate the impact of the
emollient on this attribute, a sensory analysis was carried out
on the five creams formulated as described above, by a trained
panel. The precise protocol of testing was established with physi-
cal references to distinguish and evaluate specifically this textural
attribute. Spreading of emulsions (SEM) scored between 0 and 9 is
indicated in Table 3. We observed that all emulsions were eval-
uated to be significantly different on this attribute with scores
ranging from 2.50 to 8.05. Spreading was higher with Ester 1 and
-
8/13/2019 2012_Savary Et Al._impact of Emollients on the Spreading Properties of Cosmetic Products a Combined Sensory a
5/8
G. Savary et al. / Colloids and Surfaces B: Biointerfaces 102 (2013) 371378 375
Table 3
Sensory properties and instrumental measurementsfor thedifferent emollients incorporatedeither in theoil phase (OP) or in theemulsion (EM).
Standard Ester 1 Ester 2 Ester 3 Silicone
Sensory properties
Oil phase penetration POP (min/L) 5.36c 10.1b 14.3a 5.85c 5.83c
Oil phase spreading SOP (mm2/min/L) 49.9b 29.0c 18.6d 43.0b 78.4a
Emulsion spreading SEM(score from 0 to 9) 3.55d 8.05a 2.50e 6.05b 4.95c
Instrumental measurements
Oil phase viscosity VOP (Pa s) 0.0058c 0.0152b 0.0344a 0.0063c 0.0046c
Contact angle at 0s A0s () 38.3bc 45.5b 55.6a 39.2bc 32.0c
Contact angle at 4s A4s () 12.3ab 16.2a 17.1a 8.97b 5.70b
Emulsion viscosity VEM(Pa s) 0.08c 0.16bc 0.61a 0.11c 0.24b
Texture of emulsion TEM(g s) 242c 112e 416a 324b 180d
Differentletters in thesame row indicate a significant difference between samples atp
-
8/13/2019 2012_Savary Et Al._impact of Emollients on the Spreading Properties of Cosmetic Products a Combined Sensory a
6/8
376 G. Savary et al. / Colloids and Surfaces B: Biointerfaces 102 (2013) 371378
Table 5
Physico-chemical propertiesof ingredients either pureor dispersedin the oil phase.
Densi ty Su rface tension ( mN/m) Viscosity (Pa s ) a t 1 0 s1
Pure ingredients
Ester 1 0.963 28.090.59 124103
Ester 2 0.976 Nd 3630103
Ester 3 0.932 20.160.09 10103
Silicone 0.957 17.370.07 4103
Oil phases
Ester 1 0.894 26.360.59 15103
Ester 2 0.900 25.550.91 34103
Ester 3 0.880 27.961.19 6103
Silicone 0.894 19.650.34 5103
Standard 0.827 25.030.91 6103
experiments, respectively, that could be different and induce dif-
ferent deformations of the products.
3.3. Characterization of the oil phases
To establish correlations between instrumental techniques and
in vivo sensory analysis in the case of the oil phases, some
experiments were carried out on the oil mixtures alone. Vari-
ous characterizations were performed including sensory spreadingand penetration evaluations, viscosity, and contact angle measure-
ments.
A previous preliminary study [25] has shown that the spread-
ing of pure ingredients, characterized by sensory and instrumental
analyses, was mainly influenced by the physical state of the ingre-
dients. Thus, surface tension and dynamic contact angle were not
measurable for highly viscous ingredients like Ester 2 and sensory
evaluation became particularly difficult as products could be liq-
uid as well as close to solid state. Table 5 sums up the interest
of studying the emollients solubilized in the oil phase (Phase A,
Table 2).
Incorporation of esters or silicone into the oil phase both
increases the oil phase density and leads to a lower density dif-
ference between the different emollients.Due to solubilization, and taking into account standard devia-
tion values, surface tensions of esters alone and oil phases fell into
the same range. Surface tension of silicone remained the lowest,
nevertheless gaps between emollients were strongly reduced.
Lastly, all emollients, either pure or included in the oil solution,
showed a Newtonian behaviour (curves not shown here). Com-
pared to pure ingredients, solubilization in the oil phase shifted
viscosity values (VOP) of Esters 1 and 2 to muchlower values. They
still remained significantly higher than that of Ester 3.
3.3.1. Sensory characterization of oil phases
Spreading of the five different oil phases (SOP) was evaluated by
the assessors according to a different procedure from the one used
for spreading evaluation of the emulsions. When deposited on theskin surface, the oil phases exhibited differentbehaviours from the
emulsions as the consequence of the effect of consistency. Emul-
sions formed a mound that assessors spread on the skin, whereas
the oil phases spread spontaneously without requiring any action
for the assessors. Therefore, oil phases promptly formed an oval
stain when deposited on the skin. Each sample was characterized
by a shiny appearance. The assessors were then able to visually
evaluate the surface of skin covered by the product by measuring
the corresponding area one minute after deposition.
During this time, dermal penetration of emollients may hap-
pen. As a result, we decided to ask the panellists to assess also skin
penetration of the five oil phases (POP). This property was evalu-
ated as the time necessary to observe the total disappearance of
the shiny stain formed by the sample deposited on the skin. In
this study, we assume that there was no difference in terms of
volatility between samples. This supposition was made since the
emollient represented only 11% (w/w) of the composition of the
oil phase. Among ingredients, silicone was the most volatile with a
vapour pressure of 0.2 mmHg at25 C and a boiling temperature of
210 C against for instance, Ester 3, 5.93106 mmHg and 352 C,
respectively. Measurements of skin penetrationPOPin Table 3 indi-
cate times above 5.36min. As a consequence, we assumed that the
duration of the spreading evaluation (1min) was short enough to
consider that there was no significant penetration occurrence of
samples into the stratum corneum.
Generally, the penetration ability of the emollients into the
lipophilic stratum corneum depends on both the polarity and the
molecular size of the compound [26]. This is confirmed here, pen-
etration variation among oil phases is mainly related to both the
polarity and the molecular size of ingredients (Table 1); the higher
the values of logPandMw, the longer the time needed to penetrate
into the stratum corneum as illustrated for Esters 1 and 2.
Concerning spreading, results reveal a large effect of the com-
position of the oil phase (SOP in Table 3). Values ranged from
18.6 to 78.4mm2/min/L, for Ester 2 and silicone respectively.
The standard oil phase displays an intermediary spreading of
49.9mm2/min/L. As discussed by other authors [5], the ingredi-
ents with higher molecular weight exhibit lower spreading values,as observed among esters (Table 1).
3.3.2. Instrumental characterization of oil phases spreading
Contact angle measurements for standard or emollient-oil mix-
tures were performed from initial time, as the drop of liquid was
deposited on PMMA surface, until it reached a measurable con-
stant value. At t= 0, initial contact angle values are respectively:
Ester 2 (55.63.9), Ester1 (45.52.4),Ester3(39.2 1.7), standard
(38.31.9), silicone (32.00.3). This emphasizes different affinity
of ingredients with the support. The curves of contact angle versus
time then exhibit a rapid exponential decrease, corresponding to
the rapid spontaneous spreading of each solution on the support,
until an asymptotic contact angle value is reached (after 4 s for sili-
cone(approx.6) and Ester 3 (approx.9),after14 s for Ester 2,Ester1 (approx. 12) and standard (approx. 11)). Selection of the data
for contact angles were thus restricted to the shortest time period
necessary to obtain one of these asymptotic values, that is 4s in
the case of silicone. Fig.2 shows the relaxation of the contact angle,
over a time period of 4 s, for each emollientoil mixture as well as
the profile for the corresponding drop of the five systems at t= 0 s
(immediately after deposition) and t=4s. Table 3 also displays the
values for the contact angle just after deposition (A0s) and at t= 4 s
(A4s).
Study of spontaneous spreading of a liquid on a solid surface
involves different key parameters that are: surface tension, vis-
cosity and density of liquid, surface free energy, roughness and
heterogeneity of solid support [19]. Due to solubilization of the
emollients in the oil phase, the impact of density, viscosity andsurface tension on spreading is actually reduced. When consider-
ing these last parameters for the different mixtures tested, only
differences in terms of surface tension and viscosity may explain
the contact angle results. Therefore, surface tension and volatility
differences between silicone and Ester 3 can explain the different
spreading that is observed. In the case of the ester molecules dis-
persed in oil and also oil phase, the main parameter governing the
different spreading behaviour is undoubtedly the viscosity.
It is also necessary to keep in mind that a droplet can evaporate
somewhat,depending on the wettingbehaviour and the hydropho-
bicity/hydrophilicity of the substrate [21]. In all cases, evaporation
phenomena remain negligible during the time of experiments
[21,22]. This appears evident as Orejon et al. [21] have demon-
strated that a typical evaporation time for ethanol droplets was
-
8/13/2019 2012_Savary Et Al._impact of Emollients on the Spreading Properties of Cosmetic Products a Combined Sensory a
7/8
G. Savary et al. / Colloids and Surfaces B: Biointerfaces 102 (2013) 371378 377
Fig. 2. Contact angle evolution of oil phasesdeposited on PMMA surface.
between 90s and 300s for hydrophilicand hydrophobic substrates
respectively.Initial and equilibrium contact angles values show an almost
complete wetting of the liquids on the PMMA substrate, this being
in good agreement with the roughness of PMMA plates (2m)
on the one hand, and surface free energy of the substrate on the
other hand. Alteraifi and Sasa [22] reported a critical surface ten-
sionof39mN/mforasmoothPMMA surface,which is characteristic
of intermediary properties (between PTFE around 20mN/m and
soda-lime glass 70mN/m). This is also in good agreement with the
relatively lowpolarity of theoilyliquids testedin the present study.
These measurements appear particularly relevant to anticipate
the spreading ability of a sample, as evidenced by the correla-
tion coefficients between SOP and A0s or A4s (Table 4). All these
coefficients are negative since the contact angle was inversely pro-
portional to the surface of PMMA covered by the product. Thanksto this correlation, it is possible to envisage predicting the spread-
ing of different oil phases using an instrumental method instead
of sensory evaluation. Moreover, present contact angle measure-
ments were conducted with a PMMA surface, a fairly reproducible,
easy-to-use and low cost material when compared to real as well
as synthetic skin.
Atthis step,it is possible tocompare surface properties ofPMMA
and skin surface, in terms of surface tension and chemical compo-
sition, thanks to data from the literature. A surface free energy is
reported for human skin varying from about 27 to 38.2mJm2 in
the dorsal region of skin index [27] but also on the volar forearm
or forehead skin [28]. Lowest values are obtained for a dry skin
submitted to a cleaning with delipidizing solvent and highest ones
were obtained on skin washed with soap and rinsed thoroughlyunder tap water or unwashed skin during 16h. Concerning PMMA
surfaces, values are similar or higher than skin, data in the litera-
ture ranged from 39 to 48mJ m2 depending on methods used and
cleaning of the surface [22,27,29]. Taylor et al. [30] reported even
valuesrangingfrom46to54mJ m2 related to roughness andtreat-
ment of PMMA surfaces. Both types of surface exhibit also a high
dispersive component close to total surface free energy, an acidic
component close to zero, a basic component varying from about
5 to 20 mJ m2 for PMMA and from about 0 to 28 for human skin.
This can be related to a similar chemical surface composition: epi-
dermal lipids on the one hand and ester methyl groups [31] on the
other handfor PMMAsurface.Even if PMMAsurface doesnot mimic
stratum corneum in terms of chemical composition and porosity,
contact angle measurement is a pertinentmethod to measure pure
spreading properties of oils. However, it is important to take into
account that such physical characterizations are not easy or pos-sible with any kind of sample as for example with highly viscous
liquids or the cosmetic emulsions of the present study.
3.4. Relationships betweenoil phase and emulsion properties
When formulating a cosmetic product, a major point is to know
how the properties of the end product can be governed by the
intrinsic characteristics of ingredients. Our study shows that the
relationship between the properties of emollients and the cor-
responding emulsions is not necessarily obvious. Concerning the
viscosity of emulsions (VEM), we observed a significant correlation
with VOP(Table 4). In this case, it is possible to anticipate the viscos-
ityof thecreamaccording to thecomposition of the oilphase. As an
example,Ester2 induced the highest viscosityfor both the oilphase
and the corresponding emulsion. However, concerning spreading,
thereis no linear correlation between SEMand SOP(Table 4) asan oil
phase characterizedby a highspreading performance does not nec-
essarily generate a cosmetic emulsion with the same performance;
this is illustrated with the silicone ingredient.
Emulsions are complex structures that exhibit original
behaviours influenced by many parameters including composition
and proportion of the dispersed and continuous phases, droplet
size, emulsifier type, composition and structure of the interface,
and interactions between ingredients [32]. Concerning spreading
of emulsion,our experiments shouldbe completedwith other data
to develop a predictive model with multiple parameters to be con-
sidered.
3.5. Relationship between sensory and instrumental
measurements
In conclusion, as shown in Table 4, penetration of the oil phase
(POP) was best correlated with viscosity of the oil phase (VOP) fol-
lowed by contact angle at 0 s (A0s). Spreading of the oil phase
was correlated with both A0s and A4s contact angles among the
instrumental measurements. The sensory spreading of emulsion
correlated best with the spreading of emulsion instrumentally
measured in terms of work required to move a weight on a sur-
face. Consequently, all these results made it possible to implement
physical measurements of sensory evaluations of either oil phases
or emulsions to avoid time-consuming in vivo methods.
-
8/13/2019 2012_Savary Et Al._impact of Emollients on the Spreading Properties of Cosmetic Products a Combined Sensory a
8/8
378 G. Savary et al. / Colloids and Surfaces B: Biointerfaces 102 (2013) 371378
Acknowledgements
The authors thank different contributors. Authors sincerely
acknowledge Clmentine Lachaud for instrumental measurements
and Nathalie Loubat-Bouleuc (Starinerie Dubois, France) for help-
ful discussions.
References
[1] M. Gorcea, D. Laura, Cosmet. Toilet. 125 (12) (2010) 26.[2] M.E. Parente, A. Gambaro, G. Solana, J. Cosmet. Sci. 56 (2005) 175.[3] N. Loubat-Bouleuc, OCL 11 (2004) 454.[4] E.Kim, G.W. Nam, S.Kim, H. Lee, S.Moon,I. Chang,SkinRes. Technol. 13 (2007)
417.[5] B.A. Salka, Cosmet. Toilet. 112 (1997) 101.[6] S. Nacht, J.A. Close, D. Yeung, E.H. Gans, J. Soc. Cosmet. Chem. 32 (1981) 55.[7] M.E. Parente, A. Gambaro, G. Ares, J. Sens. Stud. 23 (2008) 149.[8] I.S. Lee, H.M. Yang, J.W. Kim, Y.J. Maeng,C.W.Lee,Y.S. Kang, M.J. Rang, H.Y. Kim,
J. Sens. Stud. 20 (2005) 421.[9] G.V. Civille, C.A. Dus, Cosmet. Toilet. 106 (1991) 83.
[10] R.L. Goldemberg, C.P. De La Rosa, J. Soc. Cosmet. Chem. 22 (1971) 635.[11] R. Brummer, S. Godersky, Colloids Surf. A: Physicochem. Eng. Aspects 152
(1999) 89.[12] T.F. Tadros, S. Lonard, C. Verboom, V. Wortel, M.C. Taelman, F. Roschzttardtz,
in:T.F. Tadros(Ed.), Colloids in Cosmeticsand Personal Care, vol. 4, Wiley-VCHVerlag GmbH & Co. KGaA, Weinheim, 2008 (Chapter 8).
[13] G.Hough, A.N. Califaro,N.C. Bertola, A.E. Bevilacqua, E.Martinez, M.J. Vega, N.E.
Zaritsky, Food Qual. Pref. 7 (1996) 47.
[14] J.F. Meullenet, B.G. Lyon, J.A. Carpentier, C.E. Lyon, J. Sens. Stud. 13 (1998) 77.[15] R.A. de Wijk, L.J. van Gemert, M.E.J. Terpstra, C.L. Wilkinson, Food. Qual. Pref.
14 (2002) 305.[16] K. Kusakari, M. Yoshida, F. Matsuzaki, T. Yanaki, H. Fukui, M. Date, J. Cosmet.
Sci. 54 (2003) 321.[17] A.M. DiMuzio, E.S. Abrutyn, M.Y. Cantwell, J. Cosmet. Sci. 56 (2005)
356.[18] R.C. Daniel, J.C. Berg, Adv. Colloid Interface Sci. 123126 (2006)
439.[19] G. Kumar, K.N. Prabhu, Adv. Colloid Interface Sci. 133 (2007) 61.[20] M. de Ruijter, T.D. Blake, A. Clarke, J. De Coninck, J. Petrol. Sci. Eng. 24 (1999)
189.[21] D. Orejon, K. Sefiane, M.R. Shanahan,Langmuir 27 (2011) 12834.[22] A.M. Alteraifi,B.J. Sasa, J. Adhes.Sci. Technol. 20 (12) (2006) 1333.[23] U. Zeidler, Fette Seifen Anstrichmittel 87 (1985) 403.[24] H.A. Barnes,in: D. Petsev (Ed.), Emulsions: Structure,Stabilityand Interactions,
Elsevier, Albuquerque, 2004 (Chapter 18).[25] L. Gilbert, C. Picard, G. Savary, M. Grisel, Paper 0266. Proceedings of 5th World
Congress on Emulsion, 1214 October 2010, Lyon, 2010.[26] Y. Schiemann, M. Wegmann, P. Lersch, E. Heisler, M. Farwick, Colloids Surf. A:
Physicochem. Eng. Aspects 331 (2008) 103.[27] A. El-Shimi, E.D. Goddard, J. Colloid Interface Sci. 48 (2) (1974) 242.[28] A. Mavon, H. Zahouani, D. Redoules, P. Agache, Y. Gall, Ph. Humbert, Colloids
Surf. B: Biointerfaces 8 (1997) 147.[29] J.K. Chen, S.W. Kuo, H.C. Kao,F.C.Chang, Polymer 46 (2005) 2354.[30] R.L. Taylor, J. Verran, G.C. Lees, A.J.P. Ward, J. Mater. Sci.: Mater. Med. 9 (1998)
17.[31] J. Wang, C. Chen, S.M. Buck, Z.Chen, J. Phys. Chem. B 105 (2001) 12118.[32] P.E. Miner,in: D. Laba (Ed.),RheologicalProperties of Cosmeticsand Toiletries,
Marcel Dekker, New York, 1993 (Chapter 13).