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Colloids and Surfaces A: Physicochem. Eng. Aspects 460 (2014) 321–326

Contents lists available at ScienceDirect

Colloids and Surfaces A: Physicochemical andEngineering Aspects

journa l h om epage: www.elsev ier .com/ locate /co lsur fa

oderately stable emulsions produced by a double syringe method

. Nastasaa, K. Samarasb, M.L. Pascua,∗, T.D. Karapantsiosb

National Institute for Laser Plasma and Radiation Physics, Bucharest, RomaniaAristotle University, Chemistry Department, Thessaloniki, Greece

i g h l i g h t s

Study of oily vitamin A in watersolutions of Vancomycin emulsionsgenerated by standard emulsifica-tion techniques and by a simple andtransportable double syringe system(DSS).The addition of different stabilizers(Xanthan gum, Tween 80, Nonaethy-lene glycol monododecyl ether, andGlycerine) in the examined range ofconcentrations has no strong effecton oil droplets dimensions in water.The results show that the Tessarimethod (DSS) produces moderatelystable emulsions in a cheap, easy toapply and affordable way.

g r a p h i c a l a b s t r a c t

r t i c l e i n f o

rticle history:eceived 18 November 2013eceived in revised form 9 January 2014ccepted 17 January 2014vailable online 26 January 2014

eywords:

a b s t r a c t

Different emulsification techniques lead to emulsions with different targeted properties specific to theirintended use. In this study, emulsions are generated using several emulsification techniques. They arecompared as regards the component droplet size distribution and their stability in time. A particulartechnique based on the “Tessari” (known as double syringe system – DSS, as well) method – used originallyfor foam generation – is evaluated for emulsion production. Results show that DSS method leads toemulsions with mean droplet size about two orders of magnitude larger than in the case of emulsions

mulsionsurfactantsouble syringe systemessari methodheology

obtained by conventional high speed and high pressure homogenizers (HPH). However, DSS emulsionshave comparable viscosity behavior with the emulsions obtained by conventional methods and are stablefor time intervals of a couple of hours which is convenient for specific medical applications. Furthermore,this study evaluates the effect of small quantities of some emulsion stabilizers on the mean droplet sizedistribution of emulsions. In the examined narrow range of values no significant modifications of the

ution

mean droplet size distrib

. Introduction

Emulsions are defined as heterogeneous systems of one liquid

ispersed in another, in the form of droplets, with droplet sizeshat range from nanometers up to 100 �m. In particular conditions,mulsions may consist of oil droplets dispersed in a continuous

∗ Corresponding author. Tel.: +40 214575739.E-mail address: mihai.pascu@inflpr.ro (M.L. Pascu).

927-7757/$ – see front matter © 2014 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.colsurfa.2014.01.044

was observed.© 2014 Elsevier B.V. All rights reserved.

water phase (oil-in-water) or of water droplets dispersed in acontinuous oil phase (water-in-oil), at different oil/water ratios.Each droplet is coated with surfactant (emulsifier) molecules thatare necessary for both satisfactory emulsification (achieving smalldroplets of the dispersed phase) and emulsion stability (slowingdown phase separation) [1]. Usually, the two liquid phases are cho-

sen to be fully immiscible and chemically non-reactive whereastheir mixture is thermodynamically unstable [2]. When the two liq-uids are highly immiscible, the dispersed phase cannot exchangemolecules with the continuous phase, and therefore the effect of

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22 V. Nastasa et al. / Colloids and Surfaces A:

stwald ripening is avoided, which can lead to an increased stabil-ty of the emulsion.

Numerous studies have been conducted on emulsions due toheir widespread applications in domains with daily impact likeood, pharmaceutical and cosmetic products. Most of these studiesre devoted to assess different types of emulsification techniquesnd evaluate the emulsions stability, usually through analysis ofroplets sizes [3–8].

Emulsion’s stability depends on several factors including thehysical properties of the interfacial film, the density and viscosityf the continuous phase, the addition of surface active substancess well as the type of added surfactant/nanoparticles, the presencef electrostatic or steric barriers on the droplets, the droplets sizeistribution, the oil/water ratio, and the temperature of the mixture9,10]. The addition of surface active substances to one or both of theiquid phases affects droplet size distribution and droplet–dropletnteractions. By adding surfactants, surface tension decreases dueo adsorption of surfactant molecules at the interface, which leads,n one hand, to smaller size dispersed droplets and, on the other,nduces viscoelastic properties to droplets interfaces and so delaysroplets coalescence [11,12]. Both effects yield increased emulsiontability.

In order to create an emulsion, energy must be provided to aixture of immiscible liquids. This is usually done by mechan-

cal or pseudo-mechanical means such as rotor–stator systemshigh speed homogenizers), high pressure homogenizers, ultra-onic probes, micropore size membranes, microfluidizers, phasenversion systems, etc. An emulsion is obtained by dispersing onehase into another, that leads to an increase of the interfacial areahich is directly related to the amount of energy – W – used for

mulsification, as shown in Eq. (1) [13]

= � × �A (1)

here � is the interfacial tension and �A is the change of the inter-acial area.

By using mechanical techniques, droplet break-up leads to gen-ration of new droplets with smaller dimensions as function of thenergy provided by the emulsifier. The new interfacial area corre-ponding to these new droplets may be fully or partially covered byurfactant molecules depending on surfactant concentration in theulk. If this is not high enough to cover the new droplets’ surface or

f surfactant adsorption to the surface is very slow then drop coales-ence increases counterbalancing drop breakage. In other wordsny further droplet size reduction is not possible under the givenonditions and emulsification has reached its maximum capacity.his is why the type of surfactant and its concentration are of equalmportance with the employed emulsification technique as regardsmulsion stability.

The rotor–stator method to mix immiscible components within solution is a widely used technique due to its capabilities to pro-uce emulsions in controlled conditions by varying the rotationpeed, the type of rotor, etc. In rotor–stators, mechanical energy ishe driving force for droplet disruption. One of the most widely usedomogenizers is the Ultra Turrax system, which is utilized in thisaper too, that provides rotation speeds up to 30,000 rpm. The highressure homogenizer (HPH) is a system that mixes immiscibleomponents under a high pressure difference, with the utilized flu-ds being pushed through a small orifice with high velocity, whichreates the conditions for droplet breakage.

Although most emulsion applications on controlled drug deliv-ry focus on the generation of nanoscale droplets aiming at longasting stability of the emulsion, a method that can generate mod-

rately stable mixtures of immiscible substances in an easy andeproducible manner may have multiple applications in medicine.or instance, some dermatology treatments using emulsions ofmmiscible drugs require stability of just a few minutes to perform

ochem. Eng. Aspects 460 (2014) 321–326

the therapy [14]. Such moderately stable emulsions suffice to havedroplets dimensions of the order of microns. Nevertheless, to bereally effective for clinical treatment these emulsions should beproduced easily, in short time, in small quantities, with minimumeffort and skill, using a simple and cheap (replaceable) apparatus.The above constitute the motivation for the present work.

This paper reports for the first time the application of the“Tessari” method to generate emulsions of immiscible liquids.The “Tessari” method is a cheap, easy and readily applicabletechnique, utilized so far to generate foams [15–17]. This articlecompares emulsions produced by a double syringe system (DSS) –which applies the known “Tessari” method – with emulsions pro-duced by other established emulsification techniques, namely, tworotor–stator systems and a high pressure homogenizer (HPH). Com-parisons refer to emulsions stability in time as it is appraised fromthe initial droplet size distribution right after emulsification.

2. Materials and methods

In this study, Vancomycin (VCM, purchased from Sigma) solu-tion at a concentration of 10−4 M (0.15 mg/ml) in water wasselected as the continuous aqueous phase whereas vitamin A withconcentration of 7 × 10−2 M (20 mg/ml) in sunflower oil (commer-cially available in pharmacies) is the dispersed oily phase. Studieson this particular system have been reported in articles aiming atcontrolled drug delivery that evaluate the droplet size as functionof different emulsification parameters and of different properties ofthe involved fluids [17,18]. Other publications report on simple orlayered droplets properties and on the possibility to modify themby laser radiation [19,20–27].

The employed oil and water volumes range from 10% to 50%for the oil, and from 90% to 50% for water, respectively. In [18],using high speed and high pressure homogenizers for emulsifica-tion, it was shown that the 10% oil to 90% water is the optimal ratiofor the smallest droplet size distribution and the highest emulsionstability. In order to increase the emulsion stability, the non-ionic surfactant Polysorbate 80 (commercially known as Tween80) is dissolved in the aqueous phase at 50 ppm concentration.A 3200 ppm concentration was used only for the measurementsmade on the emulsions generated with high speed homogenizerfollowed by the HPH. Due to its low partition coefficient Polysorbate80 remains mainly in the aqueous phase.

To increase the stability of emulsions, three other substances(Xanthan gum, Nonaethylene glycol monododecyl ether and Glyc-erine) are also added to the aqueous phase. Xanthan gum is ananionic polymer with stabilizing and thickening properties com-monly used in food and cosmetic industry. It behaves like anon-Newtonian fluid with a strongly shear-thinning character. Itis used in emulsions, as it exhibits low bulk viscosity when sub-jected to high shear rates during emulsification and then becomesvery viscous when it is left to settle after emulsification, increasingthe stability of the obtained emulsion. Recent evidence supportsan additional role for polysaccharides like Xanthan gum whichmay interact with surfactants at the interface affecting also theinterfacial rheological properties of the system, e.g., increase thedilatational viscosity and so act to increase the stability of emul-sions [28]. Nonaethylene glycol monododecyl ether (C30H62O10) isa nonionic surfactant that is commonly used in cosmetic and medi-cal applications, while Glycerine is a viscous fluid that is extensivelyused in pharmaceutical procedures but has applications in the foodindustry, cosmetic and medical domains, as well.

Emulsification is performed by (a) two rotor–stator systems, (b)HPH and (c) a double syringe system (DSS). The first rotor–statorsystem consists of a stirred tank furnished with a variable speedRushton turbine. The rotor speed is varied between 300 and

Physicochem. Eng. Aspects 460 (2014) 321–326 323

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Table 1Droplets mean diameters for different types of emulsifier and oil volume percentage.

Method Conditions D[4,3] �m D[3,2] �m D[1,0] �m

Stirredtank

450 rpm 50% oil 588 453 94.7450 rpm 40% oil 482 273.6 78450 rpm 30% oil 348 262 60.7450 rpm 20% oil 315 194.3 39450 rpm 10% oil 227 149 32

UltraTur-rax

10,000 rpm 50% oil 73.4 50.5 11.110,000 rpm 30% oil 33 9.4 0.8810,000 rpm 20% oil 24.6 5.6 0.27

V. Nastasa et al. / Colloids and Surfaces A:

00 rpm. Mixing is conducted inside a baffled, cylindrical stirredank (H = 19.5 cm, inner diameter = 7 cm) with a Rushton turbine ofiameter 4.6 cm, placed 1.7 cm above the bottom. The volume ofhe mixture in the tank is 270 ml and the mixing time is 240 min.ecause of the relatively large size of the produced droplets (seeelow), right after the mixing period a 0.5 ml sample is retracted

nstantly from the vessel using a 5 mm inner diameter tube (widenough to prevent droplets jamming) and is added to a dense solu-ion of surfactant in order to prevent droplets coalescence [18,27].he second rotor–stator system is a high speed homogenizer (Ultraurrax T25). The mixing procedure is similar with that applied forhe Rushton turbine. The only difference with the first rotor–stators the mixing time, since in the case of the high speed homogenizer5 min of mixing are used.

The HPH used for these measurements is an APV2000 homog-nizer with a pressure difference across the emulsification orificef 800 bars. The volume of the mixture in the homogenizer was00 ml.

The DSS method uses two syringes connected through a smalllastic three-way stopcock typically used in transfusion of medicaluids. One syringe contains the aqueous phase and the other theily phase. For these measurements two 5 ml syringes that con-ained 4 ml of water based solution and 0.4 ml of oil were used. Thewo fluids are pumped several times through the three way stop-ock in a cyclic fashion (in–out), creating in this way the neededigh shear rate that leads to droplet breakage. This technique isomewhat similar with the HPH method, but the pressure differ-nce can reach maximum 6–8 bars [29] in the case of DSS, while thePH uses 800 bars. On the other hand, the DSS is cheaper to use andasier to apply, even outside a lab or industrial facility (e.g. a medi-al doctor’s cabinet). In the present study, 50 pumping cycles werepplied to mix the immiscible fluids and create an emulsion. Theorking conditions for all the reported experiments were similar

o the ones presented in [18].Droplet size distributions are measured by light scattering using

Malvern Mastersizer E2000 system. For verification, the dropletize distribution of some samples is measured also with a Carl Zeissicroscope system type Axiostar Plus equipped with a Canon cam-

ra. The measurements are repeated several times for each run inrder to verify the reproducibility of results and increase their sta-istical confidence. In order to evaluate the rheological propertiesf the mixture, the viscosities of the utilized immiscible fluids andf the generated emulsions are measured. For these measurements

rheometer (Physica MCR 301 Anton Paar) is used that employs aone/plate test cell to evaluate the viscosity as function of the shearate. Viscosity measurements are conducted at 25 ◦C.

. Results and discussion

The viscosity values of the two immiscible liquids withoutny additives are: �oil = 49.2 mPa s for the oily vitamin A solutionnd �aqueous = 1.08 mPa s for the aqueous Vancomycin solution. Asegards emulsification, the relatively high viscosity of the oily phaseestricts droplet breakage and so leads to emulsions with largerroplets. As for the stability, the low viscosity of the continuousqueous phase indicates an easy and fast phase separation. This isore so for mixtures with low volume percentage of the dispersed

il phase. However, in emulsions with higher than ∼35% oil, dis-ersed droplets are in contact with each other forming a networkf interconnected droplets inside the aqueous phase. In this case,hase separation is delayed due to shearing when droplets slide

nd squeeze among other droplets. This is amplified for dropletsovered by surfactants which do not only resist coalescence butlso give interfacial rigidity to droplets. In emulsions where theispersed phase is at such a high volume percentage, it is the

10,000 rpm 10% oil 0.423 0.162 0.070

HPH800 bar 50% oil 78.5 0.7 0.097800 bar 10% oil 1.241 0.337 0.072

viscosity of the emulsion and not the viscosity of the immisciblephases that dictates emulsion stability. The above discussion needsto be adjusted when additives are used that modify drastically theviscosity values.

For the droplets size distribution, three statistical mean diam-eters are considered: D[4,3] (volume or mass moment mean – DeBrouckere mean diameter), D[3,2] (surface area moment mean –Sauter mean diameter), and D[1,0] (number-length mean) whichare given by Eq. (2)

D[4,3] = ˙d4

˙d3, D[3,2] = ˙d3

˙d2, D[1,0] = ˙d

˙n(2)

where d is the individual droplets’ diameter and n is the number ofthe measured droplets [30].

All three mean diameters are presented below for comparisonpurposes. D[1,0] is weighted toward the droplet population with thelargest number of droplets in the emulsion which is usually that ofthe smallest droplets. D[4,3] is weighted toward the droplet popu-lation which occupies the largest volume in the emulsion which isusually that of the largest droplets. D[3,2] is weighted toward thedroplet population that presents the highest interfacial area in theemulsion which is usually that of an effective (not actual) dropletsize computed from the combination of different size and numberof droplets. For low volume fractions of the dispersed phase it isD[4,3] that describes better emulsion stability since large dropletsseparate freely by buoyancy. For high volume fractions of the dis-persed phase, D[1,0] describes better phase separation since smalldroplets can move between large droplets that are in contact butthey rise slowly because of their small size. In most other cases,D[3,2] are better indicators of emulsion stability. In all the dimen-sions measurements the observations were started immediatelyafter the preparation of the samples.

First, an effort is made to identify the oil volume percentage(within the examined range) that yields the smallest mean dropletsize using the aforementioned mechanical emulsifiers. Table 1shows the values of the three mean statistical droplet diametersfor emulsions produced using different ratios of oil in water con-taining Tween 80 at a concentration of 50 ppm (0.005%). It is seenthat with increasing oil fraction, droplets diameters also increaseleading, apparently, to emulsions of lower stability. Indeed, visualobservations show that the time needed for phase separation,decreases drastically as the oil percentage increases and in somecases separation is visible immediately after stopping the emul-sification procedure. This is why for the low speed rotor–statormethod the sample taken from the mixing tank is “frozen” in surfac-tant (the extracted sample is placed in a big quantity of surfactantthat suppresses the coalescence effect between droplets). There isapproximately an order of magnitude difference between D[4,3] and

D[1,0] for the stirred tank and almost two orders of magnitude dif-ference for HPH. This indicates that HPH generates not only smalldroplets but also wide droplet size distributions. Ultra Turrax iscloser to HPH performance. In every case, the smallest droplets are

324 V. Nastasa et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 460 (2014) 321–326

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speaking, though, results by light scattering agree with results fromoptical microscopy. In addition, DSS emulsion has a macroscopicmilky appearance similar to the Ultra Turrax emulsions and unlike

ig. 1. Droplet size distribution for the DSS emulsion obtained by light scatteringolume.

roduced with 10% oil in the emulsion. The rest of this study focusesn these emulsions.

Next we examine the effect of the type of emulsifier and thentensity of the emulsification process. For rotor–stator emulsifiershe intensity is reflected at the rotor speed (rpm). Table 2 presentshe mean statistical droplet diameters for emulsions containing0% oil and Tween 80 at a concentration of 50 ppm as function ofhe type of emulsifier and the process intensity.

It is evident that as the rotor speed increases the mean diame-er of droplets decreases. This effect is the result of an increasingmount of energy dissipated by the homogenizer to the samplehich leads to droplet disruption. Ultra Turrax reaches droplets

ize even at the nanometer scale. This holds also for HPH. Com-ination of Ultra Turrax with HPH practically does not reduceurther the droplet size but droplets around 60–70 nm are alreadymall enough. The emulsion obtained with the DSS technique isormed by droplets with dimensions smaller than the ones obtainedith the stirred system. On the other hand, DSS gives much largerroplets: D[4,3] and D[3,2] are almost two orders of magnitude largerhereas D[1,0] one order of magnitude larger than in the Ultra Tur-

ax and HPH systems. Yet, the smaller droplets with DSS are about �m in diameter which is a droplet dimension still capable of yield-

ng stability to an emulsion. The emulsions obtained by HPH, high

peed homogenizer and DSS also present an increased stability (e.g.he DSS emulsion containing a Tween 80 concentration of 50 ppm,resents no phase separation for as long as 2.5 h after the mixing

s stopped, while the emulsions obtained by Ultra Turrax followed

able 2tatistical mean droplet diameters for different types of emulsifiers and processntensity for 10% oil volume in the emulsion (see also [18]).

Method Conditions D[4,3] �m D[3,2] �m D[1,0] �m

Stirredtank

300 rpm 445 404 110350 rpm 351 253 62.3400 rpm 310 218 53.3450 rpm 227 149 32600 rpm 190 121 22.4

UltraTur-rax

10,000 rpm 0.423 0.162 0.07020,000 rpm 0.326 0.135 0.065

HPH 800 bar 1.241 0.337 0.072Ultra Turrax

followed by HPH20000 rpm + 800 bar 0.285 0.133 0.063

DSS 50 cycles 25 13.6 0.969

urement function (a) of the number of measured droplets and (b) of the droplet

by HPH containing 3200 ppm are stable for more than two weeks[18]).

The size distribution in the DSS emulsion is better illustratedin Fig. 1. The number of droplets with diameters less than 1 �m isabout 80% (calculated cumulatively) of the total droplets popula-tion (Fig. 1a), whereas droplets with diameters larger than 10 �moccupy about 95% (calculated cumulatively) of the oil volume(Fig. 1b).

In Fig. 2, a microscope image of an emulsion obtained with theDSS method is presented. Using the scale bar in the picture one caneasily recognize the families of droplets identified by laser diffrac-tion: the large droplets with diameters close to 20 �m and the smalldroplets with diameters close to 1 �m. Unfortunately, droplet sizedistributions from digital images are not easy to estimate due tothe excessive contact and partial overlap of droplets. Qualitatively

Fig. 2. Microscope images of an emulsion produced by the DSS method.

V. Nastasa et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 460 (2014) 321–326 325

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Table 3Statistical mean droplet diameters for the DSS emulsion following the addition ofcertain emulsion stabilizers – 10% oil in the emulsion.

Stabilizer, % of total volume D[4,3] �m D[3,2] �m D[1,0] �m

DSS emulsion with no additives 25 13.6 0.969C30H62O10 0.5% 19.0 10.1 1.00Xanthan gum 0.03% 27.6 15.2 0.97Xanthan gum 0.15% 25.5 11.8 0.99Tween 80 3% 25.0 13.6 0.97C30H62O10 0.5% + Tween 80 0.1% 25.2 13.4 1.00C30H62O10 0.5% + Tween 80 1% 25.9 9.17 1.14C30H62O10 0.5% + Tween 80 5% 30.7 17.8 1.17C30H62O10 0.5% + Tween 80 10% 29.1 16.8 1.11C30H62O10 0.5% + Glycerine 0.1% 21.7 11.6 0.98C30H62O10 0.5% + Glycerine 1% 24.7 18.8 1.07C30H62O10 0.5% + Glycerine 3% 19.2 15.4 1.07C30H62O10 0.5% + Glycerine 7% 17.2 10.1 0.97C30H62O10 0.5% + Glycerine 10% 20.8 11.6 1.01C30H62O10 0.5% + Glycerine

0.1% + Xanthan gum 0.1%26.8 13.9 0.98

C30H62O10 0.5% + Xanthan gum 0.02% 21.2 10.4 1.01C30H62O10 0.5% + Xanthan gum 0.07% 23.7 11.0 1.00

ig. 3. Droplet size distributions resulting from different emulsification techniques.

he emulsion in the stirred tank where free oil even floats at theop.

The droplet size distributions of the different emulsificationechniques expressed in number % is presented in Fig. 3. DSS yields

narrow droplet size distribution which is very advantageous foredical applications like controlled drug delivery.In Fig. 4 the viscosity results for the 10% oil emulsions are

resented. One can observe that emulsions with smaller dropletsimensions (stable homogenous emulsions) attain lower valuesnd are less dependent on shear rate than the emulsion producedn the stirred tank containing bigger droplets. For the latter, thexistence of such large droplets makes viscosity measurementsrone to errors due to phase separation inside the rheometer testell. This is inferred also from the viscosity value at 10 s−1 shearate which is close to the value of the pure oily vitamin A solu-ion: �oil = 49.2 mPa s. Moreover, the DSS emulsion exhibits similarhear-thinning behavior with the Ultra Turrax and HPH emulsions

similar slope of viscosity versus shear rate). All in all, one wouldxpect good stability against phase separation of the DSS emulsion.

ig. 4. Viscosity measurements on the emulsion function of different type of homog-nizing method.

C30H62O10 0.5% + Xanthan gum 0.1% 17.3 11.2 1.03C30H62O10 0.5% + Xanthan gum 0.3% 10.0 6.2 1.02

An effort is made, next, to improve the stability of DSS emul-sions by adding small quantities of certain additives that can actas stabilizers. Table 3 shows the droplets dimensions for differentemulsion stabilizers added to the liquid/liquid mixture.

The addition of different stabilizers in the examined range ofconcentrations has in general no strong effect on droplets dimen-sions. Some additives have minor effects on some statistical meandiameters with no clear trend whatsoever. To this end, it appearsthat there is no real benefit to add such small quantities of thesesubstances to oil–vitamin A/water–VCM emulsions produced bythe DSS mehtod. For medical applications the already obtaineddroplets size (below 20 �m) seems to yield good enough stabilityto the produced emulsions.

4. Conclusions

The main goal of this study is to compare different emulsifi-cation techniques from the point of view of droplets dimensionsand of their viscosity. It is observed that the easy to use doublesyringe system (DSS) can provide droplets with larger dimensionsthan the ones obtained with other established high-energy homog-enizing techniques (using high rotor speed or high pressure drop)but smaller than the droplets obtained with a conventional stirredtank method. At the same time, the stability and homogeneityof the emulsions obtained with the DSS technique is higher thanthose obtained by the stirred tank technique (rotation speeds up to600 rpm).

On the other hand, the DSS technique proves to be able toproduce emulsions with viscosity properties similar to the onesobtained with high speed homogenizers and HPH but at muchlower energy consumption. It is also observed that small quantitiesof emulsion stabilizers do not influence the droplets size distribu-tion in the examined range of concentrations.

Therefore, although the DSS method is not a standard emul-sification technique, it could be used to obtain moderately stableemulsions which may be important in specific medical applications.One conclusion is that by using a low concentration of nontoxic sur-factant, such as Tween 80, in emulsions produced by DSS methodone may obtain stable emulsions for time intervals long enough in

order to allow their use in medical applications. This appears to bea realistic approach since emulsions and/or foams [31,32] are cur-rently applied in medical treatment immediately after preparation.

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26 V. Nastasa et al. / Colloids and Surfaces A:

cknowledgements

This work was supported by CNCS-UEFISCDI through projectumber PN-II-ID-PCE-2011-3-0922, and by the COST ActionP1106 “Smart and green interfaces – from single bubbles and

rops to industrial, environmental and biomedical applicationsSGI)”.

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