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Study on the Formation and Properties of Liquid Crystal Emulsion in Cosmetic

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Journal of Cosmetics, Dermatological Sciences and Applications, 2013, 3, 139-144
http://dx.doi.org/10.4236/jcdsa.2013.32022 Published Online June 2013 (http://www.scirp.org/journal/jcdsa)
139
Study on the Formation and Properties of Liquid Crystal
Emulsion in Cosmetic
Wanping Zhang*, Lingyan Liu
School of Perfume and Aroma technology, Shanghai Institute of Technology, Shanghai, China.
Email: *zhwanp@yahoo.com.cn
Received January 29th, 2013; revised March 2nd, 2013; accepted March 9th, 2013
Copyright © 2013 Wanping Zhang, Lingyan Liu. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
In this paper, the formation of liquid crystal structure in preparation of emulsion and the change of those liquid crystal
structures during storage and usage were studied. Besides, the rheological and moisturizing property of the liquid crys-
tal structure emulsion was investigated as well. The results show that the liquid crystal structure at oil-water interface in
the emulsion forms gradually with cooling process after homogenization. The liquid crystal structure doesn’t change
significantly during the storage within 12 months. And after emulsion being stored for 18 months, the crystal structure
starts to decompose. Upon application on the skin, the liquid crystal structure of emulsion was found to transform into
other form with rubbing, although the liquid crystal structure still remains. The rheological data shows that liquid crys-
tal emulsion exhibits solid-like (elastic) property during storage, which is favorable for good stability. On the other hand,
liquid crystal emulsion shows typical shear-thinning property upon usage, which leads to an excellent skin sensory
feeling. And the improved moisturizing properties of such emulsion may be attributed to the liquid crystal structure.
Keywords: Liquid Crystal Emulsion; Rheology; Stability; Moisture
1. Introduction
The liquid crystal emulsion is a new type of emulsion
which is different from the traditional emulsion system.
It is the ordered arrangement of surfactant and oil mole-
cules formed at the oil-water interface, and this ordered
arrangement makes the emulsion of liquid crystal struc-
ture showing better application performances than con-
ventional emulsion systems in terms of stability, con-
trolled release and moisturizing [1-3]. The formation of
liquid crystal structure in emulsion depends not only on
the composition of the emulsion formulations, but also
the preparation processes [4,5].
The unique properties and the applications of liquid
crystal emulsion have attracted many researchers in
pharmaceutical and cosmetic product to do extensive
studies on the special structure emulsion, including pre-
paration and properties. Many specialty chemicals sup-
pliers have produced emulsifiers, e.g. many non-ionic
surfactants such as alkyl glycosides, polyglycerol esters,
phosphates etc., for preparing emulsions with liquid
crystal structure. At present, the studies of liquid crys-
talemulsion mainly focus on the theory of special sys-
tems, such as aligned structure of emulsifier mole-
cules, stability and rheological behavior, as well as
the examples of practical applications of emulsion sys-
tems [6,7].
In this paper, the formation and transformation of liq-
uid crystal structure in preparation, storage and usage
were investigated. Meanwhile the rheological be-
havior has been studied to establish the correlation be-
tween the skin sensory characteristics and the rheology
properties.
2. Experimental Section
2.1. Experimental Materials and Equipments
C16-18 APG, 99% (Cognis); Steareth-21, 99% (Croda);
sodium stearoyl glutamate, 99% (Cognis); Cetearyl al-
cohol, 99% (Cognis); caprylic/capric triglyceride, 99%
(Cognis); stearic acid, 99% (Cognis); Mineral oil, 99%
(Hangzhou Refinery); glycerol 99% (Sinopharm Chemi-
cal Reagent Co., Ltd.); Dimethicone, 99% (Dow Corn-
ing); 1,3-dihydroxy-5,5-DMH (Lonza).
FA25 High-speed shearing machine (Fluko); ECLIPSE
E200 polarizing microscope (NIKON).
*Corresponding author.
Copyright © 2013 SciRes. JCDSA
Study on the Formation and Properties of Liquid Crystal Emulsion in Cosmetic
140
2.2. Experimental Methods
2.2.1. Preparation
The formulation of emulsions comprise of oil phase,
aqueous phase and other components. The oil phase in-
cludes oil and alkyl polyglycoside emulsifiers. And the
aqueous phase includes deionized water and moisturizing
agents. Appropriate flavors and preservatives are exam-
ples of other components. A typical formulation looks
like the following: 3% emulsifier of alkyl polyglyco-
sides, 2% stearic alcohol, 3% caprylic/capric triglyceride,
5% mineral oil, 5% dimethicone, 5% glycerin, 0.2% pre-
servative, 0.2% flavor, 75.6% deionized water (w/w un-
less otherwise indicated).
Emulsions were prepared following the typical proce-
dures used for preparing O/W emulsions, i.e. the aqueous
phase (deionized water and moisturizing agents) was
heated up to 80˚C in a glass beaker. Meanwhile the oil
phase was heated up to 80˚C in another glass beaker. The
oil phase was added to the aqueous phase followed by
homogenization with F25 Ultraturrax at 13,000 rpm for 3
min. The sample was allowed to cool down to room
temperature under moderate stirring at 150 rpm, and then
stored at room temperature.
2.2.2. Polarized Optical Microscope
The samples were observed with a microscope (NIKON
ECLIPSE E200). For sample preparation, a pin-tip amount
of the emulsion was smeared on the microscope glass
slide and then quickly covered by the cover slip. The
sample was finger pressed to make it as thin as possible.
A 40× objective lens and 10 40× eye lens were used with
cross polarizers in bright field to detect birefringence.
The micrograph was taken under polarizing microscope.
2.2.3. Rheological Measurements
Steady-flow, thixotropy and dynamic viscoelastic prop-
erties were measured with a cone-and-plate geometry on
a rheometer controlled by stress (TA Instruments Co.,
Ltd. AR-2000N). The cone diameter was 40 mm. The
shear rates were from 0.0001 to 200 s1 in steady-flow
and thixotropy property measurements. The dynamic vis-
coelasticity was measured as a function of the frequency
at a small strain in the linear regions and as a function of
strain at a constant frequency. The angular frequencies
were from 0.1 to 100 s1 and the strain amplitude was
0.1%. The measuring temperature was 25˚C.
2.2.4. Moisturizing Property
The water content and the Transepidermal Water Loss
(TEWL) on the skin surface were measured by Cor-
neometer. The measurement was carried out in a room
with controlled humidity (40%) and temperature (22˚C ±
1˚C).
3. Results and Discussion
3.1. Formation of Liquid Crystal Structure
Emulsion
Emulsions with good stability can be obtained by using a
mixture of emulsifiers with preparation processes de-
scribed in this paper. The formation of liquid crystal
structure, however, shows strong dependence on the
composition of formulation and preparation process [6,
7]. By optimizing the composition of formulation and
preparation process, the liquid crystal emulsion can be
formed. In the experiment, the formation process of the
liquid crystal structure during preparation of emulsion
was studied. The polarized microscope was utilized to
monitor the sample during emulsification and homog-
enization. Photos were taken under polarized light and at
10 min, 20 min after homogenization and the end of the
preparation, respectively.
Figure 1 shows that a small amount of liquid crystal
structure was present, though disorderly, in the emulsion
droplets during the emulsification and homogenization
process. Photos taken 10 and 20 minutes after homog-
enization show increasingly higher amount of liquid
crystal structure at the oil-water interface. Furthermore,
the photo taken after homogenization and cooling show
well developed liquid crystal structures at the interface.
Therefore, it could be concluded that the liquid crystal
structure of oil-water interface in the emulsion is gradu-
ally formed with cooling after homogenization.
3.2. Stability of Liquid Crystal Structure
Emulsion
As we discussed previously, the formation of liquid
crystal structure is the result of ordered arrangement of
emulsifier and oil molecules at the oil-water interface.
However, rearrangement may occur during the storage,
Figure 1. Liquid crystal formation during and after emul-
sion preparation (under polarized lighting). (a) During ho-
mogenization; (b) 10 min after homogenization; (c) 20 min
after homogenization; (d) The final sample.
Copyright © 2013 SciRes. JCDSA
Study on the Formation and Properties of Liquid Crystal Emulsion in Cosmetic 141
leading to the change of liquid crystal structure, which
may impact storage stability and skin feel during applica-
tion. Therefore, the change of liquid crystal structure at
six months, twelve months and eighteen months of stor-
age are studied.
Figure 2 shows that liquid crystal structure doesn’t
change significantly during storage within 12 months,
though it does seem to decompose significantly after the
emulsion has been stored for 18 months. Such a phe-
nomenon could be attributed to the fact that that the for-
mation of liquid crystal structure strongly depends on the
orderly arrangement of emulsifier and oil molecules by
the way of dynamic equilibrium with the thermal motion.
The thermal motion of the oil and the emulsifier mole-
cules could reduce the ordered arrangement of the liquid
crystal structure during the storage, thereby leading to the
gradually decomposition of the liquid crystal structure
[8,9]. Actually the thermal motion is favored by the
presence of more liquid oils and emulsifiers. On the op-
posite, solid compound is not easy to move at room tem-
perature and reduce the thermal motion. It can be con-
cluded that increasing the content of solid compound
could reduce the characteristics of thermal motion of
molecules, meanwhile enhance the stability of liquid
crystal structure by adjusting the formulation structure of
emulsion.
3.3. Change of the Liquid Crystal Structure
Emulsion in Usage
It is expected that the liquid crystal structure in such
emulsions could lead to different application properties.
To assess the relationship between the liquid crystal
structure and application properties, and determine if
there are perceivable benefits, it is important to study the
changes of the liquid crystal structure during usage. Po-
Figure 2. Liquid crystal in emulsion during storage (under
polarized lighting). (a) 24 hours after preparation; (b) 6
months after preparation; (c) 12 months after preparation;
(d) 18 months after preparation.
larized microscope photographs were taken at different
stages of usage to show the changes of the liquid crystal
structure during such a process.
Figure 3 shows the significant changes of the liquid
crystal structures upon rubbing onto skin. When it is just
applied on the skin, the emulsion particles with liquid
crystal structure still exist. With the time extending, it is
conceivable that the water in the emulsion will gradually
evaporate and the relative content of the oils and the
emulsifiers will gradually increase, which will lead to the
breakdown of the emulsion particles, and turn the liquid
crystal structure with orderly distribution at oil-water
interface into lamellar liquid crystal structure [8,9]. The
photos (Figure 3) confirm that the liquid crystal structure
of emulsion changes upon rubbing, while the liquid
crystal structure still remains.
3.4. Rheological Property of Liquid Crystal
Structure Emulsion
In theory, the liquid crystal structure should result in a
few advantages than the conventional emulsion in cos-
metics applications, for example, improved stability,
moisture retention, controlled-release and good skin sen-
sory feeling. In order to probe into the correlation be-
tween the liquid crystal structure and application bene-
fits, especially stability and skin sensory feeling, the
rheological properties of the liquid crystal emulsion were
studied.
As shown in Figure 4, the dynamic viscosity of the
liquid crystal emulsion shows Bingham behavior with
shear-thinning properties. A yield stress of 31.58 Pa in-
dicates good stability can be achieved during storage and
transportation. Upon usage, the shear-thinning property
could allow the good spreading and penetrability with
finger rubbing for such emulsions. The thixotropic curve
shows a little hysteresis loop that implies the recovery of
Figure 3. Liquid crystal upon application under polarized
microscope. (a) Upon applying; (b) 5 min upon applying; (c)
10 min upon applying.
Copyright © 2013 SciRes. JCDSA
Study on the Formation and Properties of Liquid Crystal Emulsion in Cosmetic
142
(a)
(b)
(c)
Figure 4. Rheological properties of liquid crystal structure
emulsion. (a) Viscosity vs shear rate; (b) Thixotropy curve;
(c) Modulus curve.
liquid crystal structure lag behind the shear stress re-
moving. The fluidity of the liquid crystal emulsion is
restored shortly after shear stress removal. The result
indicates that the liquid crystal emulsion can show good
spreadability during application [10,11].
G’ is the storage modulus and G” is the loss modulus.
The viscoelastic curve is the G’ and G” vs frequency (ω).
These frequency (ω) dependence of dynamic moduli fur-
ther suggest that G’ response of these sample is dominant
over G” response throughout entire measured ω domain,
implying that solid-like (elastic) property dominates over
liquid-like (viscous) property in the liquid crystal emul-
sion. It means that the liquid crystal emulsion exhibits
solid-like (elastic) property in storage, which is good for
product stability. However the shear-thinning property
indicates liquid-like (viscous) property during usage,
which is quite good for skin sensory feeling. Besides, G’
and G” response increased with ω throughout all meas-
ured ω domain, though slightly. Such a viscoelastic re-
sponse is usual for surfactant stabilized O/W emulsion.
This implies that the liquid crystal emulsion can show
excellent property pertaining to emulsion used in phar-
maceutical and cosmetic applications.
3.5. Moisturizing Property of Liquid Crystal
Structure Emulsion
In order to study the influence of liquid crystal structure
emulsion on moisturizing properties. The water content
and the Transepidermal Water Loss (TEWL) on the skin
surface, before and after the application of liquid crystal
structure emulsion, were investigated by using a Cor-
neometer.
It has been reported that the increase of C16-18 fatty
alcohol in emulsions leads to increase of the formation of
liquid crystal structure [6]. In these studies, we prepared
emulsion samples with different content of C16-18 fatty
alcohol and their respective moisturizing properties were
studied.
Figure 5(a) shows that there is no change on the water
content of skin surface by using the different emulsion
with the different liquid crystal structure, but the differ-
ent liquid crystal structure affect the Transepidermal
Water Loss on the skin surface. Figure 5(b) shows that
the Transepidermal Water Loss decreases with increasing
the liquid crystal structure of emulsion. The good mois-
turizing properties of the emulsions with liquid crystal
structure could be attributed to the fact that large amount
of water molecules can be entrapped within the ordered,
crystalline structures of the liquid crystals by association
with the hydrophilic groups of the emulsifier molecules.
The latter forms ordered & multilayer structures to-
gether with oil and other molecules at the water/oil inter-
face of the emulsion.
4. Conclusion
In this paper, the formation of liquid crystal structure
Copyright © 2013 SciRes. JCDSA
Study on the Formation and Properties of Liquid Crystal Emulsion in Cosmetic 143
(a)
(b)
Figure 5. Moisturizing properties of liquid crystal structure
emulsion. (a) Influence on the water content of skin surface;
(b) Influence on the Transepidermal Water Loss on the skin
surface.
during preparation of emulsion, the change of such struc-
ture during storage and cosmetic applications as well as
the rheological properties were investigated. The results
show that the liquid crystal structure gradually forms at
the oil-water interface of the emulsion particles with
cooling process after homogenization. The liquid crystal
structure exists at the oil-water interfaces of emulsion
particles. The liquid crystal structure doesn’t change sig-
nificantly during the storage within 12 months. However
after being stored for 18 months, the crystal structure
starts to decompose. Upon applying onto skin, the liquid
crystal structure with orderly distribution at oil-water
interface turns into lamellar liquid crystal structure. The
liquid crystal emulsion shows solid-like (elastic) rheol-
ogical properties, which can lead to good product feel,
spreadability and other favorable attributes associated
with cosmetic applications. The liquid crystal structure
emulsion also shows good moisturizing property, which
could be attributed to the entrapment of the water mole-
cules within the emulsifier layers of the liquid crystal
structure.
5. Acknowledgements
The authors thank Hu Jing in Shanghai Institute of Tech-
nology for establishing the methods to measure the rhol-
ogy properties, Zheng Yunyun in Shanghai Research In-
stitute of Fragrance & Flavor Industry for support with
the moisturizing properties studies.
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Oleyl ether sulfates (OEnS) with different EO addition numbers (nEO = 3, 5, 7) were systematically explored from synthesis, structural identification, surface properties and aggregation behavior to their application in the preparation of emulsion, where the structures of the prepared OEnS were identified by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (¹H NMR). By analyzing the krafft temperature and surface properties of OEnS, the results showed that the higher the EO number, the lower the krafft temperature and CMC, with OE7S krafft temperature below 0 °C and CMC reaching 0.018 mmol/L, while the adsorption performance decreased with increasing EO number. Transmission electron microscopy (TEM) and polarized optical microscopy (POM) were used to observe the aggregation behavior, while dynamic light scattering(DLS)could be used to analyze the size of aggregates and small angle X-ray scattering (SAXS) was used to characterize the liquid crystal structure. It was found that OEnS solutions with concentrations up to CMC or above could form micellar aggregates of large size and had a lamellar liquid crystal structure at high concentrations, with the layer spacing increasing with the amount of EO. By studying the effect of OEnS on the formation of liquid crystal structures in emulsion, it was found that the higher the EO addition number, the smaller the size of the emulsified particles and the denser the lamellar gel network phase structure formed, combined with the study of rheological properties to prove that the emulsion had good storage stability and shear thinning properties.
Article
This study focuses on the fate of excipients contained in topical emulsions once applied on the skin. The aim was thus to develop a methodology to characterize the residue left on the skin shortly after emulsion application. To this end, both the role and the impact of the different excipients on the formation and properties of the residue left on the skin surface once a product is applied were investigated. To that purpose, an O/W emulsion composed of an ester as oily phase, an emulsifier (alkylpolyglucoside-based vehicles), a polymer and a humectant (hydrophilic excipient) was first developed. Then, systems with fewer ingredients were prepared to understand their respective role in the residual film. This residual film was studied in vivo by means of biophysical instrumental methods, all being performed on the participants' forearm. Results highlighted the major role of the ester giving a bright and hydrophobic residue. While the surfactant structuration as the presence of glycerin and polymer provided a specific water distribution inside the residue on the skin surface. Finally, this work evidenced the ingredients organization in the residue depending on the systems composition, with a particular stratification on skin surface which could be considered in the formulation strategy for efficient active delivery and skin protection.
Article
Introduction: Three original cosmetic formulations containing retinol as an active component with liquid crystal, lamellar, and lipid bases were prepared. The formulas contain different concentrations of retinol, that is, 0.5%, 0.3%, and 0.15%. Objectives: The aim of the study was to evaluate a spectrophotometric method for assessing the quantity of retinol in the nine cosmetic products and to determine the viscosity of each formula. Materials and methods: The formulations were tested for stability; final product testing was preceded by sample weighing and pH measurement as well as exposure to the light source from xenon lamp that maps solar radiation in the range of 310-800 nm. Microbiological purity test was performed according to the PN-EN ISO 29621:2011 method and viscosity carried out using a cone-plate digital rheometer (DV-III Brookfield, version 3.0) on 0.5 cm3 emulsion samples at 32°C. The retinol content in preparations was assayed by UV spectrophotometry. Results: Each of prepared cosmetic products with retinol storing in a room temperature occurred to be stable. The liquid crystal emulsion has the higher viscosity than lamellar and lipid emulsions. Although the retinol concentration in lipid serum was determined with high accuracy, the method has some limitations associated with differences between the lipid cosmetic base and the lamellar and liquid crystal sera. Nevertheless, the UV spectrophotometric method described herein is a simple and highly accurate approach for determining the retinol content in lipid cosmetics: Its coefficient of correlation was R2 = 0.9982 with a relative standard deviation (n = 3) in the range of 0.5%-1.5%. Conclusion: The presented UV spectrophotometric method represents an effective tool for fast and accurate determination of retinol content in lipid formulations. Probably, the method could be used in studies of other retinol-based preparations, for example, medications, and for determining the effective life of retinol-containing products in storage.
Article
Due to the circadian rhythm regulation of almost every biological process in the human body, physiological and biochemical conditions vary considerably over the course of a 24-h period. Thus, optimal drug delivery and therapy should be effectively controlled to achieve the desired therapeutic plasma concentrations and therapeutic drug responses at the required time according to chronopharmacological concepts, rather than continuous maintenance of constant drug concentrations for an extended time period. For many drugs, it is not always necessary to constantly deliver a drug into the human body under disease conditions due to rhythmic variations. Pulsatile drug delivery systems (PDDSs) have been receiving more attention in pharmaceutical development by providing a predetermined lag period, followed by a fast or rate-controlled drug release after application. PDDSs are characterized by a programmed drug release, which may release a drug at repeatable pulses to match the biological and clinical needs of a given disease therapy. This review article focuses on thermoresponsive gating membranes embedded with liquid crystals (LCs) for transdermal drug delivery using PDDS technology. In addition, the principal rationale and the advanced approaches for the use of PDDSs, the marketed products of chronotherapeutic DDSs with pulsatile function designed by various PDDS technologies, pulsatile drug delivery designed with thermoresponsive polymers, challenges and opportunities of transdermal drug delivery, and novel approaches of LC systems for drug delivery are reviewed and discussed. A brief overview of all academic research articles concerning single LC- or binary LC-embedded thermoresponsive membranes with a switchable on-off permeation function through topical application by an external temperature control, which may modulate the dosing interval and administration time according to the therapeutic needs of the human body, is also compiled and presented. In the near future, since thermal-based approaches have become a well-accepted method to enhance transdermal delivery of different water-soluble drugs and macromolecules, a combination of the thermal-assisted approach with thermoresponsive LCs membranes will have the potential to improve PDDS applications but still poses a great challenge.
Thesis
Depuis plus de 20 ans, de nombreuses méthodes et techniques non invasives ont été développées en vue de mesurer le plus objectivement possible, les propriétés (physico-chimiques, sensorielles, etc.) des produits cosmétiques. Ces méthodes visent à évaluer leur innocuité et leur efficacité, et deviennent d’autant plus perfectionnées que les processus d’élaborations de ces produits deviennent complexes et innovants.Au cours de ces travaux de thèse, une étude multi-échelle, de l'évolution structurale d'émulsions cosmétiques représentatives des crèmes mises sur le marché a été menée, afin de prédire leur stabilité tant texturale que microbiologique.L’étude du lien entre l’organisation structurale de ces émulsions avec leur composition et leur stabilité a été un des premiers défis à relever. Grâce à une technique non destructive ultrasonore permettant d’accéder aux propriétés micro-rhéologiques (propriétés viscoélastiques observée lors d'une sollicitation harmonique de cisaillement à quelques MHz), en association à différentes techniques classiques de caractérisation (microscopie optique, rhéologie basse fréquence, etc.) ; il a été possible de corréler les paramètres micro-rhéologiques obtenus à des modèles physiques reliant structuration interne et stabilité dans les émulsions considérées. Les résultats ont montrés que les données micro-rhéologiques sont sensibles aux variations de compositions (concentration) et d’organisations microscopiques des micelles au sein des émulsions (floculation, coalescence, etc.).Ensuite, le suivi de l’évolution d’une bactérie type (Pseudomonas fluorescens) dans des émulsions possédant des structures internes différentes, a montré d’une part la sensibilité de la micro-rhéologie vis-à-vis de la présence de bactéries dans le milieu, et d’autre part, l’impact de la structure et l’organisation des micelles sur le développement de ces bactéries.Finalement, la micro-rhéologie apparait être une méthode de mesure innovante et adaptée à l’échelle industrielle apportant une valeur ajoutée lors du développement de formulations cosmétiques. D’un point de vue sécuritaire, le dépistage précoce de contaminations biologiques par la détection d’instabilités (de changements) structurales au sein des émulsions, pourrait représenter une avancée majeure lors des phases de production et de commercialisation des produits cosmétiques.
Article
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Oil-in-water (o/w) emulsions for cosmetic use, such as lotions and creams, are complex multiple-phase systems, which may contain a number of interacting surfactants, fatty amphiphiles, polymers and other excipients. This study investigates the influence of two synthetic cationic polymers, Polyquaternium-7 and Polyquaternium-11, and the natural anionic polymer, gum of acacia, on the rheology and microstructure of creams prepared with a non-ionic mixed emulsifier (cetyl stearyl alcohol-12EO/cetyl alcohol) using rheology (continuous shear, and viscoelastic creep and oscillation), microscopy and differential scanning calorimetry (DSC). A control cream containing no polymer was also investigated. The semisolid control cream was structured by a swollen lamellar gel network phase formed from the interaction of cetyl alcohol and the POE surfactant, in excess of that required to stabilize oil droplets, with continuous phase water. Endothermic transitions between 25 and 100 degrees C were identified as components of this phase. Incorporation of cationic polymer into the formulation caused significant loss of structure to produce a mobile semisolid containing larger oil droplets. The microscopical and thermal data implied that the cationic polymer caused the swollen lamellar gel network phase to transform into non-swollen crystals of cetyl alcohol. In contrast, incorporation of gum of acacia produced a thicker cream than the control, with smaller droplet sizes and little evidence of the gel network. Microscopical and thermal data implied that although there were also interactions between gum of acacia and both the surfactant and the swollen gel network phase, the semisolid properties were probably because of the ability of the gum of acacia to stabilize and thicken the emulsion in the absence of the swollen lamellar network.
Article
Targetting an encapsulated drug towards a diseased organ, with the possibility to control its release at the right place and at the right time, is one among numerous questions asked to the new nanotechnologies. We present a partial answer with the example of recently elaborated lipidic nanocapsules. Liquid crystals play a role in the preparation techniques, and possibly in the delivery mechanisms of the active principle in situ. We also know that liquid crystalline behaviours are involved at the membrane level and are essential in the cell machinery. Drug nanocarriers could find their way, as do viruses, in the liquid crystalline context of cell organization.
Article
The phase behaviour of a mixed surfactant system was studied in order to determine the role of surfactants in the stability of paraffin emulsions. The study was carried out by means of phase diagrams. The different phases were characterized by Small and Wide Angle X-ray Scattering (SAXS/WAXS), Polarized Optical Microscopy (POM) and Differential Scanning Calorimetry (DSC). The results showed that the nonionic and ionic surfactants, used in industry for paraffin emulsions, possess high Krafft points and both form lamellar interdigitated gel structures. Phase behaviour of the water/mixed surfactant pseudoternary system indicated that, lamellar liquid crystalline aggregates are formed at very diluted surfactant concentrations (≈98 wt% water), even at low nonionic/ionic surfactant weight ratio (10/90). Therefore, lamellar liquid crystalline aggregates coexist with excess water, at the surfactant compositions used to obtain stable paraffin emulsions (2–4 wt% of mixed surfactant). Theses aggregates could contribute to the high kinetic stability of the paraffin emulsions.Graphical abstractHighlights► Surfactants form Lβ phases at room temperature, preventing desorption at the oil–water interface. ► In the mixed surfactant system, Lα phase is observed at low surfactant concentrations. ► Multilayers consisting of lamellar aggregates may enhance emulsion stability.
Article
We observed the crystallization and polymorphic transformation processes of palm stearin (PS) dispersed in nanometer-size oil-in-water emulsion droplets (nanometer-size droplets, average diameter 120 ± 30 nm) using DSC and in-situ synchrotron radiation X-ray diffraction (SR-XRD) techniques. The nanometer-size emulsion droplets were prepared by using four types of highly hydrophilic polyglycerine fatty-acid mono-esters, in which a polar moiety was made of 10 polymerized glycerins (decaglycerine, 10G) and nonpolar moieties were lauric, myristic, palmitic, and stearic fatty acids. When decaglycerin monolaurate (10G1L) was employed, crystallization temperatures (Tc's) of high-melting and low-melting fractions of PS were 8 and 2 °C, which were decreased from 31 and 3 °C for the bulk PS. However, the Tc of the high-melting fraction of PS was increased as the fatty-acid moiety was changed to myristic (10G1M), palmitic (10G1P), and stearic (10G1S) acids; in particular, the Tc became 38 °C with 10G1S. Furthermore, the crystallization of the high-melting fraction with 10G1M, 10G1P, and 10G1S exhibited only wide-angle SR-XRD patterns without small-angle SR-XRD patterns, indicating that these crystals formed thin films in the nanometer-size emulsion droplets that did not diffract small-angle SR-XRD patterns. We did not observe these features in our previous work on PS crystallization in bulk and micrometer-size emulsion droplets (Sonoda, et al. J. Am. Oil Chem. Soc. 2004, 81, 365). It was assumed that the freezing of a high-melting emulsifier may act as a template for nucleation of a high-melting fraction of PS, whose effects are more remarkable in nanometer-size emulsion than in micrometer-size emulsion, due to the tight packing of the hydrophobic region of the interfacial emulsifier membrane of the nanometer-size emulsion.
Article
Recent research on the role of the continuous phase in emulsions is reviewed. Special attention is given to the structured continuous phases such as lyotropic and thermotropic liquid crystals and gel networks. The implications in the formation, stability and properties of emulsions are discussed. Some recent applications, particularly in templating for the preparation of new materials, are also introduced.
Article
A gel emulsion with high internal oil phase volume fraction was formed via an inversion process induced by a water-oil ratio change. The process involved the formation of intermediate multiple emulsions prior to inversion. The multiple emulsions contain a liquid crystal formed by the surfactant with water; this was both predicted by the equilibrium phase diagram as well as observed using polarization microscopy. These multiple emulsions were more stable compared to alternative multiple emulsions prepared in the same way with a surfactant that does not form liquid crystals. While the formation of a stable intermediate multiple emulsion may not be a necessary condition for the inversion to occur, the transitional presence of a liquid crystal proved to be a significant factor in the stabilization of the intermediate multiple emulsions. The resulting gel emulsion contained a small fraction of the liquid crystal according to the phase diagram, and it exhibited excellent stability.
Article
Emulsion structures are reviewed with special consideration given to the conditions in emulsions for topical applications with more phases than the traditional two liquids. The fundamentals of emulsions containing liquid crystals and vesicles are described, focussing on the dependence of the volume ratios of liquid crystals and vesicles on the surfactant content.
Article
The ability to control finely the structure of materials remains a central issue in colloidal science. Due to their elastic properties, liquid crystals (LC) are increasingly used to organize matter at the micrometer scale in soft composites. Textures and shapes of LC droplets are currently controlled by the competition between elasticity and anchoring, hydrodynamic flows, or external fields. Molecules adsorbed specifically at LC interfaces are known to orient LC molecules (anchoring effect), but other induced effects have been poorly explored. Using specifically designed amphitropic surfactants, we demonstrate that large-shape transformations can be achieved in direct LC/water emulsions. In particular, we focus on unusual nematic filaments formed from spherical droplets. These results suggest new approaches to design new soft LC composite materials through the adsorption of molecules at liquid crystal interfaces.
Influence of Other Ingredients on the Formation of Liquid Crystal in APG System
  • W P Zhang
  • L Y Liu
W. P. Zhang and L. Y. Liu, "Influence of Other Ingredients on the Formation of Liquid Crystal in APG System," China Surfactant Detergent & Cosmetics, Vol. 40, No. 1, 2010, pp. 35-39.
Study on the Influence of Emulsion Technology on the Formation of Liquid Crystal Structural
  • W P Zhang
  • L L Zhu
W. P. Zhang and L. L. Zhu, "Study on the Influence of Emulsion Technology on the Formation of Liquid Crystal Structural," China Surfactant Detergent & Cosmetics, Vol. 39, No. 1, 2009, pp. 35-38.