Surfactants, Micelles, Microemulsions and Liquid Crystals

185 Pages·1984·4 MB·English

by  A. Weiss (eds.), D. Roux, A. M. Bellocq, P. Bothorel (auth.)

Progress in Colloid & Polymer Science • Vol. 69
Progress in
Colloid & Polymer Science
Editors: H.-G. Kilian (Ulm) and A. Weiss (Munich)
Suoeactants, Micelles, Microemulsions
and Liquid Crystals
Editor:
A. Weiss (Munich)
Steinkopff Verlag • Darmstadt 1984
ISBN 3-7985-0655-8
ISSN 0340-255 X
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IV
Contents
Roux, D., Bellocq, A. M., and Bothorel, P.: Effect of the molecular structure of components on micellar interactions in
microemulsions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Angel, M., Hoffmann, H., L6bl, M., Reizlein, K., Thurn, H., and Wunderlich, I.: From rodlike micelles to lyotropic liquid
crystals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Heusch, R.: Mizellquellung und die Bildung von Solubilisaten, Mikroemulsionen und Emulsionen . . . . . . . . . . . . 29
Stilbs, P. and Lindmann, B.: NMR measurements on microemulsion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Niirnberg, E. und Pohler, W.: Zur Kenntnis von 3-Komponenten-Mikroemulsionsgelen- 3. Mitteilung: Vergleichende
Untersuchungen von Mikroemulsionsgelen und verwandten Systemen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Usselmann, B. und Miiller-Goymann,C . C.: Struktureller Aufbau yon Cholesterol-Polyoxyiithylenfettalkohol~ither-Was-
ser-Mischungen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Ntirnberg, E. und Pohler, W.: Zur Kenntnis von Transparenten 3-Komponenten-Tensidgelen- 4. Mitteilung: Der Gelcha-
rakter optisch isotroper Tensid-H20-Paraffinsysteme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Sackmann, H.: Uber das Phasen- und Struktursystem thermotroper Fltissiger Kristalle . . . . . . . . . . . . . . . . . . . . . 73
Reizlein, K. and Hoffmann H.: New lyotropic nematic liquid crystals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Eich, M., Ullrich, K., and Wendorff, J. H.: Investigations on pretransitional phenomena of the isotropic-nematic phase
transition of mesogenic materials by means of electrically induced birefrigence . . . . . . . . . . . . . . . . . . . . . . . . 94
Te~ak, t~., Strajnar, E, Milat, O., and Stubi~ar, M.: Formation oflyotropic liquid crystals of metal dodecyl benzene sulpho-
nares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Rys, F. S.: Kritische Eigenschaften von Lipid-Doppelschichten am Hauptphaseniibergang . . . . . . . . . . . . . . . . . . . 106
Holzwarth, J. und Rys, E S.: Beobachtungen einer kritischen Triibung und Verlangsamung am Hauptphaseniibergang von
Phospholipid-Membranen, bestimmt mit der Laser-Temperatursprungmethode. . . . . . . . . . . . . . . . . . . . . . . . . 109
Wendel, H. and Bisch, P. M.: On the interplay of microscopic order and macroscopic properties in solvent-saturated lipid
films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
MOiler, K., Eisenbach, C., Schneller, A., Ringsdorf, H. und Kothe, G.: Kernspinlabel-Untersuchungenz ur Struktur und
Dynamik von fltissigkristallinen Hauptkettenpolymeren . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
Cackovic, H., Springer, J. und Weigelt, F. W.: Aggregationseffekte von Polymeren mit mesogenen Seitengruppen in
L6sung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
Haase, W. and Pranoto, H.: Properties of liquid crystalline polymers in the electric field . . . . . . . . . . . . . . . . . . . . 139
Kurzend6rfer, C.-P., Altensch6pfer, Th. und V61kel, H.-J.: Tensideinflul3 auf den Wasserablauf an harten Oberflgchen 145
Spei, M.: R6ntgenkleinwinkeluntersuchungena n tensidbehandelten Faserkeratinen . . . . . . . . . . . . . . . . . . . . . . . 154
Rupprecht, H. und Daniels, R.: Cosorption von p-Hydroxybenzoes~iureestern( Parabene) mit Nonylphenol-Polyglykolen
an por6sem SiO2 aus Wasser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Schwuger, M. J., v. Rybinski, W. und Krings, P.: Adsorption yon Tensiden an Zeolith A . . . . . . . . . . . . . . . . . . . . 167
HeB, W. und Klein, R.: Massen- und Selbstdiffusion in Systemen wechselwirkender Brownscher Teilchen . . . . . . . . 174
V
Progress in Colloid & Polymer Science Progr Colloid & PolymerS ci 69:1-11 (1984)
Effect of the molecular structure of components on micellar interactions
in microemulsions*)
D. Roux, A. M. Bellocq, and P. Bothorel
Centre de Recherche Paul Pascal (CNRS), Talence, France
Abstract: The effect of the chemical nature of oil, alcohol and surfactant on interactions in
W/O microemulsions has been studied by light scattering and photon correlation spec-
troscopy. The influence of the chain length and of the branching of oil has been investigat-
ed. For this purpose the following oils have been used: dodecane, octane, cyclohexane
and trimethyl 2-2-4, pentane. The alcohol chain length has also been varied from 5 to 7
carbons. In order to examine the influence of the surfactant structure we have used SDS
and a methyl SDS.
All these molecular changes lead to very different behavior in the interactions. Indeed
the second virial coefficients vary in a large range from positive to very negative values
indicating that interactions in the studied systems change from hard spheres to largely
attractive. It seems that the important parameters are the length for alcohol, the molecular
volume for oil and the polar head area for surfactant. A very simple intermicellar potential
is proposed. It allows to account for all the obtained light scattering results. This potential
is due to Van Der Walls interactions and the interpenetration between micelles is taken
into account. The most important values of the attractive interactions appear in the over-
lapping region. It is shown that the proposed potential is proportional to the penetrated
volume.
Key words: Microemulsion, micelles, micellar interactions.
1. Introduction potential for inverted micelles did not permit in most
cases to give a complete analysis of data. Recently two
The scattering properties of microemulsions were
of us have calculated the intermicellar energy potential
first investigated by Hoar and Schulman [1]. Since that
time, these systems have attracted considerable atten- between W/O microemulsions [6]. In this calculation
tion. In some part of the phase diagram their structure interactions have been evaluated for penetrable par-
ticles formed by spherical aqueous core and concentric
can be pictured as dispersions of water droplets sur-
rounded by a film of surfactant and alcohol molecules spherical layers. Attractive interactions are calculated
in a continuous medium mainly made of oil. Light through integration of semi-empirical interatomic
scattering techniques have been extensively applied to potential over the various regions of interacting
these systems, since these methods provide informa- micelles. This potential allows the interpretation of the
tion on micellar sizes and interactions between drop- effects of size and alcohol on the behavior of micro-
lets [2, 3, 4, 5]. emulsions [5].
Previous results have shown that in water in oil(W/ Our interest in this paper lies mainly devoted in
O)microemulsions a large range of interaction forces investigating the effect of the molecular structure of the
can be obtained by varying chemical composition. various components which form a microemulsion -
Modern theories of fluids were used by several authors alcohol, oil and surfactant - on the interactions be-
to explain the light scattering experimental results tween W/O miceUes. For this purpose we have studied
[3, 4]. The difficulty in evaluating the interaction a large number of W/O microemulsions by static and
dynamic light scattering. Indeed, the static experi-
*) Lecture given at the 31' h Conference of the Kolloid Gesell- ments give access to the second virial coefficient B of
schaft, Bayreuth October 11-24, 1983. the osmotic pressure which is directly related to the
2 Progressi n Colloid & PolymerS cience, VoL 69 (1984)
interaction potential. Moreover, study of the concen- H - qbk13T 1+ B C ~2 + . . . )
tration dependence of the diffusion coefficient D at Vm +-3
moderate concentrations allows the determination of
the virial coeffident a of D. Several recent theories rel- where B and C are virial coefficients. B is direcdy relat-
ate this virial coefficient a to the interaction potential ed to the interaction potential U(r) by:
[7, 8, 9]. So in this paper, we have compared the expe-
j u(~)
rimental B and a values with those calculated by using
e = - 4/-/ ( e - ~-;f - 1)/'2 dr
a simplified interaction potential. Pm
In the following, we will first recall some theoretical
results (sect. II), then we describe the experimental In the limit of very small volume fractions, the
procedure (sect. III), and intensity and diffusion coef- osmotic pressure can be approximated by
fident measurements (sect. IV). In section V we will
present an analytical interaction potential between W/
O micelles, then we will give the results of the calcula- Um ~ 1+~-
tion of virial coefficients B and a. In the concluding
section we will discuss the experimental and theoreti- From the above equations one can deduce:
cal results.
~b = 1 ( I+B~) (2)
I KV,n
It appears that droplet size and the second virial
2. T h e o r e t i c a l b a c k g r o u n d
coefficient B can be extracted from a study of#/I in the
For unpolarized light the excess scattering of the low concentration range. In addition, results obtained
particles assumed to be of a constant size over that of from more concentrated solutions allow one to deter-
the continuous phase is [10]: mine the variation of the osmotic compressibility.
Modern theories of fluids have been used by several
I(0) = (1 + cos20) rv , , qb S(q) P(q) authors to explain microemulsion experimental
results. One of the main conclusions of these theories
where q = 4Fin/2o sin 0/2 is the scattering wave vec- is that in dense liquids the spatial structure, which can
tor, 0 is the scattering angle, Vm is the volume of the be represented either by the function of pair distribu-
micelle, ~ the micellar volume fraction and tion g(r) or by the thermodynamic properties, is to a
large extent determined by steric repulsions between
( dnl8 0],4)-1 close particles. The attractive or repulsive effects are
K = 2H2n 2 \ d~] (1)
treated as perturbation of hard spheres. Vrij et al. con-
sider that the intermicellar interaction potential in
with n the refractive index and ;to the light wavelength W/O microemulsions can be expressed as the sum of
in vacuo. P(q) is the intraparticle form factor: we set two terms Uus and Ua [3]. The hard sphere contribu-
P(q) - i for particles under study since their radius is tion to the osmotic pressure Hus is described by the
less than 100 A. S(q) is the structure factor. In the limit equation of state proposed by Carnahan and Starling
q -* o, S(q) is related to the osmotic pressure 17 by the [12]. Only binary interactions are considered in the
compressibility relation [11] term of perturbation Ha. The total osmotic pressure of
the solution can be written as H = Fins + HA with
s(o) = (oFil- '
?ff¢/ kt3T 1 + qbus + qb2s - qbSns
Hus -
Vus (1 - q~us)3
where ks is the Boltzman constant and T the absolute
temperature. The relation between compressibility
Ha kBT A ¢)2
and interaction between particles is not easy. One of
Vra 2
the simplest ways to have an idea of the interactions is
to develop the osmotic pressure according to the virial 4H 1
I Ua(r) re dr
formula. FI can be written as a function of different A - kBT Vm
powers of ~: 2RHs
Roux et aL, Effect of the moleculars tructure of components on micellar interactions in microemulsions 3
Ua(r) is the perturbation to the hard sphere poten-
24 i ( 1 - e - ~ ) r 2d r
tial Uus(r). Ckus is the volumic fraction of hard spheres B = 8 +-R~us
of radius Rus. #us is related to ¢~ by c/),s/C/) = a. The RHS
second virial coefficient deduced from the whole
where 8 is the hard sphere contribution.
expression of H is written B' = 8a + A. In this model,
In opposition, there is still some discrepancy
the scattered intensity is:
amongst the calculations for 3 presented by different
authors [7, 8, 9]. However, in the case where U(r) =
I(c/)) = K V m Uus(r) + UA(r), it is possible to write down a relation
for 3 which has the same structure as the preceeding
(1 - a~b)4
one, that is
1 + 4a¢~ + 4a2~b2 - 4a3~b3 + a4~ 4 + A~(1 - a~) 4
°
(3) L F(x) (1 - e - ax
The fit of the experimental I(¢~) curve by a least where 3o is the hard sphere contribution.
square method allows the determination of three para- A complete treatment has been given by Feldherof
[7] who obtains:
meters, KVm, a and A from which we can deduce the
micellar radius and the second virial coefficient B'.
Moreover, the autocorrelation function of the scat-
30 = 6.44
tered light is given by [13]:
and
g(2)('t') = 1 + e -2Dq2r
F(x) = 12x - 15/(8x 2) + 27/(64x 4) + 75/(64x s) (6)
where D is the translational diffusion and q the wave
vector. D is related to osmotic pressure by D = Vm/[ Others treatments have been proposed by Batche-
OFl/O~ where Vm is the volume of the miceUe and [ the lor [8] and Goldstein and Zimm [9]. The a values
friction coefficient between micelle and continuous derived from these three calculations being very close,
phase. in the following we only give the result obtained with
In the low concentration range, D can be written as the Feldherof equation (eq. 6).
V]
kBT 3. Experimental part
D - Do (1 + a~b) with Do -
6 H 17 RH (4)
a) Sample preparation
r/is the viscosity of the continuous phase, Ru the hy= The studied samplesa re quaternarym ixtureso f water, oil, alco-
hol and surfactant. N-dodecane (D), N-octane (O), isooctane( tri-
drodynamical radius of the micelle. The virial coeffi-
methyl 2-2-4-pentane) (I) and cyclohexane( C) have been used as
cient a is related to that of the osmotic pressure by the
oil; 1-pentanol( C5), 1-hexanol( C6), 1-heptanol (C7) as alcohol;
equation sodium dodecyl sulfate (S) and sodium methyl-1 dodecyl sulfate
(M) as surfactanc For the systems containing SDS and dodecane
several microemulsionso f water/surfactantr atio (W/S expressedi n
a = B - 3 volume) rangingf rom 1.74 to 3.50 were studied in order to obtain
size variation. All the studied systemsa re locatedo n the surface of
demixion of the one-phase volume. They are designated in an
3 represents the dynamic part which takes into abridgedf orm by the surfactantf ollowedb y the alcohola nd the oil,
then as an example a microemulsionf ormed with SDS, pentanol
account the volume fraction dependence of the friction
and dodecane is named S-C5-D. SDS of quality puriss was pur-
coefficient [. Both the static and dynamic contribu-
chased from Touzart and Matignon;t he sodium a-methyl dodecyl
tions of a are related to the interaction potential of par- sulfate was synthetizedi n the laboratory according to the method
tides U(r). The expression for B is well established in of ref. [14]. The other compounds are Fluka products. The overall
compositiono f the studieds ystems are giveni n table 1 and ref. [5].
the case of rigid spherical particles of radius Rus with a
A schematicd escriptiono f the W/O studiedm icellesi s giveni n
pair interaction potential U(x) where x = r/Rus and r is
figure 1. The water cores are surrounded by a mixedf ilm of surfac-
the distance between the centers of the two particles. tant and alcoholm olecules.T hese miceUesa re dispersedi n a corn-
4 Progress in Colloid & Polymer Science, VoL 69 (1984)
Table 1. Volumic compositions of microemulsions made with different oils, and with a-methyll-SDS. The compositions of the S-Alcohol-D
microeemulsions are given in ref. [5].
S-C6-O S-C6-C S-C6-I S-C6-D M-C~-D M-C26-D M-C~-D M-C2z-D
W/S 2.55 2.55 2.55 2.55 1.75 2.55 2.75 2.55
Water 19.25 21.36 19.33 19.56 13.78 20.51 15.93 20.43
Oil 55.19 55.90 56.46 52.94 65.59 55.47 63.73 55.24
Surfactant 7.51 8.33 7.54 7.66 7.49 8.05 5.80 8.02
Alcohol 18.05 14.41 16.67 19.83 13.14 15.96 14.53 16.31
large concentration range. They allow the dilution of the studied
microemulsions approximately 30 times. Solutions of vohimic
micellar fractions ranging from 0.01 to 0.30 have been prepared by
this method. One has observed a kinetic effect in systems for which
the second virial coefficient is positive (this corresponds to the less
ph,.. ./<. ?L , \
attractive interactions, tables 2 and 3). Indeed in these cases, the
solution becomes clear only a few hours after mixing of the compo-
nents. Compositions of the continuous and dispersed phases are
reported in tables 2 and 3. The composition of the continuous phase
i [ , , , , ,~o I -~ I is characterized by the molecular alcohol oil ratio AC/oil. It is
known that the continuous phase penetrates into the micelle [16];
usually one assumes that its composition is not changed. In this
,,,- . /,?
assumption it is possible to calculate the alcohol volume contained
in the micelle: the used alcohols being very slightly soluble in water,
we consider that the whole alcohol contained in the micelle AM is
only located at the interface. Hence the composition of the interface
is defined by the molecular alcohol surfactant ratio (tables 2 and 3).
For a given alcohol, as the W/S ratio increases the alcohol concen-
tration in the continuous phase increases, whereas in the interface
Fig. 1. Schematic picture of a W/O microemulsion this concentration decreases. For a given W/S ratio, the alcohol
concentration in the continuous phase depends on alcohol and oil.
The AC/oil ratio decreases as the alcohol chain length increases and
as the oil chain length decreases. Microemulsions formed with the
branched surfactant contained less alcohol than those formed with
plex solvent named ,continuous phase". The continuous phase SDS; in these systems the decrease of the alcohol concentration is
contains primarily oil and alcohol but also a small amount of water. much more marked in the continuous phase than in the interface.
Analysis of light scattering data in terms of size and interaction This means that the quantity of surfactant molecules necessary to
requires an extrapolation of the results to zero concentration, there- solubilize a given amount of oil and water is less with Me-SDS than
fore it is necessary to use a dilution procedure which keeps constant with SDS.
both the size and composition of miceUes. The composition of the
continuous and dispersed phases of the studied microemulsions has
been determined by using the dilution procedure described by Gra-
ciaa et al. [2]. The validity of such a method has been checked by b) Method
Taupin et al. [15] by means of neutron scattering. Indeed variable The various liquid components of the microemulsions (oil, wa-
contrast gives information about the internal structure of the object. ter and alcohol) were first filtered on fine sintered glass - 1.4 tim)
It has been shown that structure and composition of the elementary before preparation of the samples and then the solutions were cen-
droplet is unchanged up to a water volume fraction equal to 0.3 in trifugated at 5000 rpm for 30 mn. Refractive indexes have been
microemulsions where attractive forces are not very strong. measured using a Pulffich refractometer. The usual sin 8 correction
The volume fraction of the micelles has been defined as: was made to allow for the angular variation of the size of the scatter-
ing volume. Correction of solid angle was also carried out. The
V~ + V~ + Vs angular range studied was 30 ° < 8 < 150 °.
The intensity and the correlation function of the scattered light
~= v
were successively measured with a laser beam (Argon ion laser,
Spectra Physics Model 165,2o = 5145 A). All the static and dynam-
Where V is the total volume, Vs the volume of surfactant and ic measurements were made at 21.5 + 0.5 *C.
lz'~t and V~, are respectively the volumes of alcohol and water con- Measurements of the viscosities of the continuous phases were
tained in the miceUes. Straight dilution lines are obtained in a very carried out using an improved Oswald-like viscosimeter.
Roux et aL, Effect of the molecular structure of components on micellar interactions in microemulsions 5
Table 2. Effect of alcohol and W/S ratio on the sizes and virial coefficients of microemulsions formed with SDS and dodecane. R and B are
determined by the extrapolation method R' and B' by the Vrij method, a) volumic ratio of total water to surfactant; b) molecular ratio of
alcohol to SDS in the micelle; c) molecular ratio of alcohol to do&cane in the continuous phase
S-C~-D S-C2-D S - C ~ 6 - D S-C2-D S-C36-D S-C~-D S-C~-D S-C27-D S-C~- D
W/S a 2.55 1.74 1.75 2.32 2.90 3.50 2.55 2.74 3.48
AM/S b 2.99 2.71 2.58 2.8 2.61 1.9 2.69 2.7 2.82
At/C12 c 0.4 0.29 0.24 0.263 0.34 0.454 0.22 0.25 0.34
R (irk) 50+6 6 2 ± 7 47.6+1 6 4 + 4 6 6 + 1 7 0 + 2 54 6 2 + 2 6 6 + 3
R' ( A ) 4 8 + 1 6 3 ± 5 6 6 ± 1 7 4 ± 2 56 61 + 2 6 5 + 3
B - 2 3 + 3 - 2 7 + 3 - 0 . 5 ± 0 . 5 - 4 . 4 ± 1 - 6 . 1 ± 1 - 8 . 8 + 2 +6 4 ± 2 3 ± 3
B' - 1 . 5 ± 0 . 5 - 3 . 8 ± 1 - 6 ± 1 -9 .2_+2 +5 3 ± 2 2 + 3
RH (A) 55 ± 10 65 ± 10 52 ± 5 67 ± 10 69 ± 10 61 73 ±2 75 ± 10
a - 1 8 ± 3 - - 2 1 ± 3 - -5 .8±1 - -9 .7±1 - - 1 2 ± 1 +1 - 0 ± 1 - 0 ± 1
Table 3. Effect of oil and surfactant on the virial coefficients
S-C6-0 S-C6-C S-Cs-I S-C6-D M - C 6 ~ - D M-C,2-D M-C~-D M-C27-D
W/S a 2.55 2.55 2.55 2.55 1.75 2.55 2.55 2.751
AM/S b 2.45 1.68 2.46 2.77 2.25 2.45 2.4 2.44
AC/o c 0.306 0.114 0.17 0.36 0.14 0.22 0.16 0.17
R 55.6 68. 62. 54. 75. 61. 57.
R' 54. 68. 65. 56. 60. 58.
RH 61.5 61. 61. 65. 71. 64.
B - 0 . 10 . 4 . - 10 . - 1 3 . - 1 6 . - 4 . - 9 .
B' 4 . 5 5 . - 5 . - 9 . - 3 . - 4 .
a - 2 . - 3 . 4 . - 8 . - 2 0 . - 7 .
In the determination of the dilution line, the transition from tur- 4. Light scattering results
bid polyphasic state to transparent one-phase system is visually
observed. However this observation becomes very difficult in the We have measured the scattered intensity 190 (which
low concentration range. Moreover we have observed that in some
is expressed as the Rayleigh ratio in cm- 1) and the diffu-
cases, scattered intensity varies largely in the vicinity of the demi-
sion coefficient at 0 = 90 ° by the various microemul-
xion line. Therefore, all the investigated samples have been pre-
pared in the photometer according to the procedure described in sions as a function of volumic fraction. Figures 2 and 3
the previous paper [5]. show examples of intensity and diffusion coefficient
6 Progress in Colloid & Polymer Science, Vol. 69 (1984)
1.10 4 (cm-i) D/Do
-'~x
4C "#+h.--+ ~ +-+" + S'C~ -D
/ \ \ ®
30
' ~ ' ~ , ~ . . ~ s-c~-D (~)
2C / / s-c -o k\ '% i;o
1C
"~ - ~ " ' 0 -~-0'-~-0'"~- - '°~-0'""- -'0~~0-~ - S C3$ I " D . . . . 0.I1 . . . . 0.J2 ~ *
~ ' ~ i i S-07 -D
0 0.1 0.2 # -
• 5-C6-0
15~_ I. 104 (cm- I ) * 5-0s-0
|D/D~ " S-Cs -I
If~,~___ ÷ s-c,-o
5-~-0
1 s-%-c
0,5 , , i
0 0.05 ~ ~-
Fig. 3. a) influence of alcohol and surfactant; b) influence of oil on
3l- fd "'.& diffusion coefficient
lY O__o
0 0.1 0.2 03 #
Fig. 2. Scattered intensities at 8 = 90 ° versus the micellar volume
fraction, a) influence of alcohol and surfactant; b) influence of oil
independent of the wave vector in the low concentra-
tion range (@ < 0.04). For most of the concentrated
microemulsions, I and D remain independent of q.
However in the case of the S-C5-D and M-C6-D
variation versus @fo r various microemulsions. Both microemulsions which exhibit a strong variation of I
variations I(@) and D(@) are strongly dependent on the and D versus @, an angular dependence is observed in
alcohol, the surfactant and the oil. All the curves I(@) the concentration range around the extremum of I and
show in the studied concentration range a maximum D. These variations are related to a critical behavior of
for a certain @maxv alue. D(@) curves relative to most of these microemulsions [18]. Similar behavior has been
the studied microemulsions presents a minimum. found recendy in the three-phase microemulsion sys-
However for the microemulsions S-C7-D the transla- tems [19].
tional diffusion coefficient is found independent of @. Figure 4 shows plots of @/I versus @i n the low con-
Data analysis shows that the observed differences of centration range (@ < 0.1) for different microemul-
intensity are due to various causes: sions. Analysis of these data allows one to derive by
extrapolation at infinite dilution (eq. 2) the apparent
i) variation of size and interactions
radius R of the micelle and the second virial coefficient
ii) vicinity of a critical point
B (tables 2 and 3). As well as the microemulsions for
iii) variation of the increment of refractive index, this
which I is independent of q, these two values R and B
latter varies between 0.077 in the pentanol-
have also been determined by analysis of the whole
dodecane system and 0.009 in the hexanol-
I(@) curve by using equation 3 proposed by Vrij [3].
isooctane microemulsion.
The corresponding values R' and B' are reported in
Besides this we have measured the angular depend- tables 2 and 3. In most cases values of R and B obtained
ence of the V, component of the scattered light and of by the two methods are in the limit of experimental
the D coefficient at different volume fractions. It accuracy in good agreement. However this agree-
appears that for all the studied systems I and D are ment is only obtained as one takes volumic frac-