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Papers by Véronique Sadtler

Journal of Physical Chemistry B, 2010

The association behavior of light-responsive azobenzene modified poly(sodium acrylate)s (AMPs) wi... more The association behavior of light-responsive azobenzene modified poly(sodium acrylate)s (AMPs) with C(12)E(6) (hexa-oxyethyleneglycol n-dodecyl ether) surfactant micelles swollen with dodecane was investigated using dynamic light scattering, UV spectrophotometry, and capillary electrophoresis techniques. AMPs complexes with oligoethyleneglycol n-alkyl ether show promising properties as emulsifiers for the light-triggered control of inversion of emulsions and the present work aims at giving new insights with respect to the nature of their photoresponse. Depending on the dodecane amount, the size of the spherical surfactant micelles was varied with radii ranging from 4 to 8 nm. AMPs can be viewed as long PAANa chains bearing several randomly distributed azobenzene groups. First, the binding behavior of the AMPs chains to the micelles swollen with various amounts of oil was thoroughly studied under dark-adapted conditions, which means that most azobenzene groups are in their trans conformation (less polar than the cis conformation obtained under UV irradiation). The binding of azobenzene to surfactant micelles, which leads to the formation of AMPs/surfactant complexes, is controlled by the energy of transfer of the azobenzene moiety from water to the micelle core and by the energy of loops formation since multiple attachments of azobenzene to a single micelle are expected with long AMPs chains. We show that the change in the energy of transfer of the azobenzene group between water and micelles upon increasing the amount of dodecane within the core of micelles was quite weak (not exceeding 0.7 kT). Within the investigated range of curvature, we observed that the energy of loops formation, which decreases with increasing micelle size (decrease of curvature or increase of oil amount) was similarly weak. The effect of the presence of dodecane on the photoresponse of the complex formation was investigated. It is shown that exposure to UV light markedly weakens the association of the AMPs with surfactant within a domain of surfactant concentrations much larger for swollen micelles than for pure surfactant micelles. Consequently, we suggest that emulsion inversion triggered by light could be due to the photomodulation of the binding of AMPs to colloidal objects with various and/or specific curvatures including surfactant mesophases or small size emulsion droplets.

Phosphorus, Sulfur, and Silicon and the Related Elements, 1996

ABSTRACT Dimorpholinophosphates 1, with a single perfluoroalkyl chain, self-aggregate when disper... more ABSTRACT Dimorpholinophosphates 1, with a single perfluoroalkyl chain, self-aggregate when dispersed in water to give tubular structures which reversibly transform into giant vesicles when heated. Compounds 1 also allow the preparation of stable reverse water-in-fluorocarbon emulsions destined to pulmonary drug delivery. None of this could be achieved with non-fluorinated analogs.

Macromolecular Rapid Communications, 2010

This study reports the first PEO-coated polymer nanoparticles synthesis by miniemulsion polymeriz... more This study reports the first PEO-coated polymer nanoparticles synthesis by miniemulsion polymerization of nano-emulsions prepared by the low-energy emulsification method called EIP. The surfactant used was Brij 98, a PEO based non ionic commercial surfactant. The partial phase diagram of the system water/Brij 98/styrene was first determined. The Emulsion Inversion Point technique was then used on the water/Brij 98/styrene system to the formation of styrene-in-water nano-emulsions. After miniemulsion polymerization, particle sizes as low as 36 nm were obtained. To the best of our knowledge, this method had not been used for polymerizable system up to now.

Langmuir, 2004

Two kinds of transitions can occur when an emulsified water-oil-ethoxylated nonionic surfactant s... more Two kinds of transitions can occur when an emulsified water-oil-ethoxylated nonionic surfactant system is cooled under constant stirring. At a water-oil ratio close to unity, a transitional inversion takes place from a water-in-oil (W/O) to an oil-in-water (O/W) morphology according to the so-called phaseinversion-temperature method. At a high water content, a multiple w/O/W emulsion changes to a simple O/W emulsion. The continuous monitoring of both the emulsion conductivity and viscosity allows the identification of several phenomena that take place during the temperature decrease. In all cases, a viscosity maximum is found on each side of the three-phase behavior temperature interval and correlates with the attainment of extremely fine emulsions, where the best compromise between a low-tension and a nottoo-unstable emulsion is reached. The studied system contains Polysorbate 85, a light alkane cut oil, and a sodium chloride brine. All transitions are interpreted in the framework of the formulation-composition bidimensional map. Figure 4. Viscosity (Pa.s) and conductivity (mS/cm) variation as the temperature decreases for FW ) 0.5.

Journal of Colloid and Interface Science, 2010

The analysis of incoherent polarized steady light transport is reported as a convenient technique... more The analysis of incoherent polarized steady light transport is reported as a convenient technique for the drop size determination in highly concentrated oil-in-water emulsions. The studied system consists in heptane-in-water emulsions stabilized with a copolymeric surfactant (Synperonic PE®/L64). Hundred grams of parent emulsions, at two volume fractions of dispersed phase (φ=0.958 and 0.937) were prepared using a semi-batch process. Then, they were diluted with the aqueous phase to obtain volume fractions ranging from 0.886 to 0.958. The use of a copolymeric surfactant allows the dilution of the highly concentrated emulsions without any change in the particle size distribution as confirmed by laser diffraction measurements. We found that the polarization technique allows the determination of the film thickness between water drops rather than their sizes. Consequently, we propose a geometrical relationship to determine an average drop size from the film thickness. The sensitivity of this alternative technique to detect changes in average drop size was studied by changing some process and formulation parameters. Drop size determination in highly concentrated emulsions via this method is useful since the measurement protocol neither involves dilution nor induces structural changes in the emulsion.

Journal of Colloid and Interface Science, 2004

The behavior of a commercial sucrose stearate blend has been examined by means of various experim... more The behavior of a commercial sucrose stearate blend has been examined by means of various experimental techniques (differential scanning calorimetry, light polarization and electron microscopy, and rotational rheometry). A partial phase diagram in water has been established. It shows that the binary system forms a lamellar lyotropic mesophase and that the melting behavior is characterized by a lamellar gel-lamellar liquid crystalline phase transition. The identification of the liquid crystalline phase has been carried out from textural observation using polarization microscopy and freeze-fracture electron microscopy. At low surfactant concentrations, the phase transition has been followed through rheological experiments. Furthermore, a shear-induced transition, from the lamellar phase (sheets of surfactant bilayers including a few large multilamellar vesicles) to an onion phase, has been observed above a critical temperature of 43 • C. The vesicles so obtained did not relax over more than 3 weeks. The presence of a small ratio of distearate in the sugar ester blend seems to be the key to vesicle formation at low surface-active material concentration.

Journal of Colloid and Interface Science, 2002

The stability of oil-in-water emulsions prepared using dextran, a natural polysaccharide, hydroph... more The stability of oil-in-water emulsions prepared using dextran, a natural polysaccharide, hydrophobically substituted with phenoxy groups, was studied. The evolution of the emulsion droplet size was investigated as a function of polymer concentration (Cp = 0.2 to 1% w/w in a water phase) and the degree of phenoxy substitution (τ = 4.2 to 15.7%). For the highest τ values, emulsions, which presented submicrometer droplets, were stable over more than 4 months at room temperature. The most substituted polymers clearly showed a better efficiency to lower the surface tension at the oil/water interface. DexP did not induce real viscosification of the continuous phase. The linearity of the particle volume variation with time, and the invariability of the volume distribution function, proved that Ostwald ripening was the main destabilization mechanism of the phenoxy dextran emulsions. The nature of the oil dispersed phase drastically affected the behavior of emulsions. While the emulsions prepared with n-dodecane presented a particle growth with time, only few size variations occurred when n-hexadecane was used. Furthermore, small ratios of n-hexadecane in n-dodecane phase reduced the particle growth due to the lower solubility and lower diffusion coefficient in water of n-hexadecane, which acted as a ripening inhibitor. C 2002 Elsevier Science (USA)

Journal of Colloid and Interface Science, 2006

Surface tension properties of an enzymatically synthesized equimolar mixture of trehalose mono- a... more Surface tension properties of an enzymatically synthesized equimolar mixture of trehalose mono- and didecanoate in aqueous solutions have been determined. At 20 degrees C a critical micellar concentration (CMC) of 50 micromol/l and a minimal surface tension of 28 mN/m have been obtained. Above the CMC, it has been shown that up to a concentration of 42 wt%, and in a 20-60 degrees C temperature range the sugar ester aqueous solutions do not form any crystalline structure, nor present any phase transition, and the trehalose decanoate molecules form an isotropic worm-like micellar phase. The rheological properties indicate however a more complicated picture in the same concentration and temperature ranges. In steady shear, the viscosity of the trehalose decanoate solutions do not exhibit any shear rate dependence from 1 to 100 s(-1) for concentrations up to 42 wt%. Below 0.8 wt%, the viscosity remains constant and close to that of water; then, between 0.8 and 23 wt%, the viscosity shows a quadratic increase with surfactant concentration. For higher concentrations, up to 42 wt%, no further significant increase in viscosity is observed. In oscillatory shear experiments, the solutions exhibit viscoelastic properties. The observed rheological behavior as a function of concentration and temperature may be due to a progressive evolution of the trehalose decanoate molecular associations: as the concentration increases, the system evolves towards an entangled and/or partially branched or cross-linked micellar network, and eventually a multiconnected network of cross-linked micelles.

Journal of Applied Polymer Science, 2002

ABSTRACT The production of porous polymeric particles is attractive for a large number of applica... more ABSTRACT The production of porous polymeric particles is attractive for a large number of applications and can be achieved by various techniques. Although numerous production schemes exist for glassy polymers, difficulties arise for soft, rubbery materials that need a chemical crosslinking step, such as elastomers. This is particularly true for poly(dimethylsiloxane) (PDMS), which shows the lowest glass-transition temperature among the polymers. Recent studies suggest in situ hydrogen bubble formation or vacuum drying of water droplets dispersed in the polymer matrix in order to generate porous PDMS structures. In this work we report early results based on the chemical crosslinking of water in PDMS emulsion droplets in a mechanically stirred thermostated water vessel. This approach is shown to lead to high porosity PDMS beads (ca. 10−3 m particle diameter) with an open structure whose properties (diameter and porosity) are strongly influenced by the starting composition (solvent, surfactant, and polymer types and ratios), as well as the operating parameters (agitation and temperature). The possible uses of these derived beads are discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 967–971, 2002

Industrial & Engineering Chemistry Research, 2003

ABSTRACT The regions corresponding to different emulsion morphology occurrences have been clearly... more ABSTRACT The regions corresponding to different emulsion morphology occurrences have been clearly identified on a bidimensional formulation−composition map. Multiple emulsions spontaneously form when there is a conflict between the formulation and composition effects. In such systems the most external emulsion is found to be unstable when the formulation effect is produced by a single surfactant. The use of a proper surfactant−polymer mixture allows one to strongly inhibit the mass transfer and to considerably lengthen the equilibration between interfaces. As a consequence, the multiple emulsion can be stable enough to be used in encapsulation and controlled-release applications. The area where multiple emulsions occur and their characteristics (conductivity and amount of encapsulated external phase) are reported for a system containing a sorbitan ester lipophilic surfactant and a diblock poly(ethylene oxide)−poly(propylene oxide) hydrophilic polymer, as a function of the formulation and composition, for a single-step process in which a specific amount of mechanical energy is supplied. An increase in the oil viscosity is found to alter the map and to modify the multiple emulsion characteristics. The application of the results to emulsion-making technology is discussed.

Industrial & Engineering Chemistry Research, 2010

ABSTRACT We studied the energy consumption per unit volume during preparation of highly concentra... more ABSTRACT We studied the energy consumption per unit volume during preparation of highly concentrated water-in-oil emulsions in a two-step semibatch process. In particular, we studied the effect of two process variables, the water addition flow rate (Qw) and the agitation speed (N). The oil used for emulsion preparation was n-dodecane, the surfactant was sorbitan monooleate (Span 80) and deionized water was used for the dispersed phase. The results obtained showed that two steps were required to get complete incorporation of the dispersed phase and a homogeneous and stable gel-emulsion. With the help of independent physical characteristics measurement performed at the end of the preparation process, we established two functional relationships, relating storage modulus (G′) with energy consumption (Ev), (G′ Ev0.6), and average liquid cell size (Rm) of the dispersed phase with energy consumption (Ev), (Rm EV−0.3). A structural scaling law can be deduced that relates the elastic modulus to the reciprocal of the square of the average liquid’s cell size of the gel-emulsion, corroborated by independent measurements and predicted by recent published models.

Industrial & Engineering Chemistry Research, 2006

... Lionel Choplin, ‡ and Jean-Louis Salager* †. ... 3, Chapter 2. (4) Salager, JL; Miñana-Perez,... more ... Lionel Choplin, ‡ and Jean-Louis Salager* †. ... 3, Chapter 2. (4) Salager, JL; Miñana-Perez, M.;Perez-Sanchez, M.; Ramirez-Gouveia, M.; Rojas, CI Surfactant−Oil−Water Systems near the Affinity Inversion Part III: The two Kinds of Emulsion Inversion. J. Dispersion Sci. Technol. ...

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011

Poly(ethylene oxide)-covered polystyrene nanoparticles were prepared by free radical miniemulsion... more Poly(ethylene oxide)-covered polystyrene nanoparticles were prepared by free radical miniemulsion polymerization after using an original low energy emulsification procedure called Near-PIT method. This procedure consisted in heating the initial monomer emulsion up to a temperature close to the phase inversion temperature (PIT) but lower. The surfactants used were commercial Brij® 78 and Brij® 700 and mixtures of both. The Near-PIT

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2006

When the emulsion inversion from abnormal to normal morphology is induced by continuous stirring ... more When the emulsion inversion from abnormal to normal morphology is induced by continuous stirring only, it takes place through the formation of a multiple emulsion in which the external phase is continuously included as droplets in the dispersed phase drops. In the studied case the system exhibits an initial O/W morphology, then a w/O/W multiple one before inverting into a W/O emulsion. The general trend reported in the literature is that the higher the initial water content, the longer the incorporating process to swell the drops in order to attain the critical dispersed phase volume that triggers inversion. The present study reports, for nonionic systems with a given hydrophilic-lipophilic balance (HLB = 6) and 7 wt.% of surfactant concentration, that this trend is found to be unexpectedly reversed when the initial water content increases beyond 80%. This anomalous result is attributed to an indirect increase in the lipophilicity of the formulation due to the variation of the interfacial surfactant mixture with the water/oil ratio, and to the formation of liquid crystals at high water contents.

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011

Oil-in-water nanoemulsions were prepared with mixtures of a non-ionic surfactant and an amphiphil... more Oil-in-water nanoemulsions were prepared with mixtures of a non-ionic surfactant and an amphiphilic anionic polyelectrolyte (HMPA1). Initial droplet diameters and ageing rates of emulsions were investigated as a function of various formulation and storage parameters (storage temperature, nature and amount of oil and stabilizers). The main ageing process was identified as Ostwald ripening, at least within the first weeks. Emulsion

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2002

Oil-in-water emulsions were prepared using dextran, a natural polysaccharide, hydrophobically mod... more Oil-in-water emulsions were prepared using dextran, a natural polysaccharide, hydrophobically modified with phenoxy groups. Emulsions were prepared by two different processes which were sonication and microfluidization. The average diameter of oil droplets and the stability with time of the resulting emulsions were investigated as a function of polymer concentration (Cp0/0.1 Á/1% w/w in water phase) and the degree of polymer grafting (t0/4.2 Á/15.7%). The microfluidization process allowed to realize emulsions with lower initial particle size than the sonication method. For the highest degrees of grafting and for Cp values ]/0.2% w/w, submicronic emulsions were obtained, which were stable for more than 4 months at room temperature. Interfacial measurements at the n-dodecane/water interface clearly showed a better efficiency of the most substituted polymers to lower the surface tension. #

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1999

Liquid fluorocarbons with high gas-dissolving capacity, high fluidity, low surface tension, excep... more Liquid fluorocarbons with high gas-dissolving capacity, high fluidity, low surface tension, exceptional biological inertness, are in clinical trials for the treatment of acute respiratory failure by liquid ventilation. Fluorocarbons are able to reopen collapsed alveoli and facilitate the exchange of the respiratory gases. They also constitute a promising carrier for administration of drugs via the pulmonary route. Since pharmaceuticals are usually not soluble in fluorocarbons, we have designed and prepared reverse water-in-fluorocarbon emulsions. These emulsions are stabilized by perfluoroalkylated surfactants with a dimorpholinophosphate head group. They can be sterilized by heat or filtration through a 0.22 mm membrane, and are stable (initial mean droplet diameter = 0.17 mm, 0.26 mm after 1 year at 25°C). Various drugs, including antibiotics, vasodilators and anticancer agents, were incorporated in the aqueous phase of the emulsions. Preliminary biocompatibilty tests are encouraging. An in 6itro study at 37°C of the release of 5,6-carboxyfluorescein encapsulated in the internal phase of a reverse water-in-perfluorooctyl bromide emulsion was significantly slower than for a reverse water-in-octyl bromide emulsion (4% vs 37% of release after 6 h) or for a standard isopropyl myristate reverse emulsion stabilized by Span 80 (48% after 6 h). This is assigned to the extreme hydrophobic character of fluorocarbons which act as a physical barrier to diffusion of encapsulated hydrophilic compounds.

Journal of Physical Chemistry B, 2010

The association behavior of light-responsive azobenzene modified poly(sodium acrylate)s (AMPs) wi... more The association behavior of light-responsive azobenzene modified poly(sodium acrylate)s (AMPs) with C(12)E(6) (hexa-oxyethyleneglycol n-dodecyl ether) surfactant micelles swollen with dodecane was investigated using dynamic light scattering, UV spectrophotometry, and capillary electrophoresis techniques. AMPs complexes with oligoethyleneglycol n-alkyl ether show promising properties as emulsifiers for the light-triggered control of inversion of emulsions and the present work aims at giving new insights with respect to the nature of their photoresponse. Depending on the dodecane amount, the size of the spherical surfactant micelles was varied with radii ranging from 4 to 8 nm. AMPs can be viewed as long PAANa chains bearing several randomly distributed azobenzene groups. First, the binding behavior of the AMPs chains to the micelles swollen with various amounts of oil was thoroughly studied under dark-adapted conditions, which means that most azobenzene groups are in their trans conformation (less polar than the cis conformation obtained under UV irradiation). The binding of azobenzene to surfactant micelles, which leads to the formation of AMPs/surfactant complexes, is controlled by the energy of transfer of the azobenzene moiety from water to the micelle core and by the energy of loops formation since multiple attachments of azobenzene to a single micelle are expected with long AMPs chains. We show that the change in the energy of transfer of the azobenzene group between water and micelles upon increasing the amount of dodecane within the core of micelles was quite weak (not exceeding 0.7 kT). Within the investigated range of curvature, we observed that the energy of loops formation, which decreases with increasing micelle size (decrease of curvature or increase of oil amount) was similarly weak. The effect of the presence of dodecane on the photoresponse of the complex formation was investigated. It is shown that exposure to UV light markedly weakens the association of the AMPs with surfactant within a domain of surfactant concentrations much larger for swollen micelles than for pure surfactant micelles. Consequently, we suggest that emulsion inversion triggered by light could be due to the photomodulation of the binding of AMPs to colloidal objects with various and/or specific curvatures including surfactant mesophases or small size emulsion droplets.

Phosphorus, Sulfur, and Silicon and the Related Elements, 1996

ABSTRACT Dimorpholinophosphates 1, with a single perfluoroalkyl chain, self-aggregate when disper... more ABSTRACT Dimorpholinophosphates 1, with a single perfluoroalkyl chain, self-aggregate when dispersed in water to give tubular structures which reversibly transform into giant vesicles when heated. Compounds 1 also allow the preparation of stable reverse water-in-fluorocarbon emulsions destined to pulmonary drug delivery. None of this could be achieved with non-fluorinated analogs.

Macromolecular Rapid Communications, 2010

This study reports the first PEO-coated polymer nanoparticles synthesis by miniemulsion polymeriz... more This study reports the first PEO-coated polymer nanoparticles synthesis by miniemulsion polymerization of nano-emulsions prepared by the low-energy emulsification method called EIP. The surfactant used was Brij 98, a PEO based non ionic commercial surfactant. The partial phase diagram of the system water/Brij 98/styrene was first determined. The Emulsion Inversion Point technique was then used on the water/Brij 98/styrene system to the formation of styrene-in-water nano-emulsions. After miniemulsion polymerization, particle sizes as low as 36 nm were obtained. To the best of our knowledge, this method had not been used for polymerizable system up to now.

Langmuir, 2004

Two kinds of transitions can occur when an emulsified water-oil-ethoxylated nonionic surfactant s... more Two kinds of transitions can occur when an emulsified water-oil-ethoxylated nonionic surfactant system is cooled under constant stirring. At a water-oil ratio close to unity, a transitional inversion takes place from a water-in-oil (W/O) to an oil-in-water (O/W) morphology according to the so-called phaseinversion-temperature method. At a high water content, a multiple w/O/W emulsion changes to a simple O/W emulsion. The continuous monitoring of both the emulsion conductivity and viscosity allows the identification of several phenomena that take place during the temperature decrease. In all cases, a viscosity maximum is found on each side of the three-phase behavior temperature interval and correlates with the attainment of extremely fine emulsions, where the best compromise between a low-tension and a nottoo-unstable emulsion is reached. The studied system contains Polysorbate 85, a light alkane cut oil, and a sodium chloride brine. All transitions are interpreted in the framework of the formulation-composition bidimensional map. Figure 4. Viscosity (Pa.s) and conductivity (mS/cm) variation as the temperature decreases for FW ) 0.5.

Journal of Colloid and Interface Science, 2010

The analysis of incoherent polarized steady light transport is reported as a convenient technique... more The analysis of incoherent polarized steady light transport is reported as a convenient technique for the drop size determination in highly concentrated oil-in-water emulsions. The studied system consists in heptane-in-water emulsions stabilized with a copolymeric surfactant (Synperonic PE®/L64). Hundred grams of parent emulsions, at two volume fractions of dispersed phase (φ=0.958 and 0.937) were prepared using a semi-batch process. Then, they were diluted with the aqueous phase to obtain volume fractions ranging from 0.886 to 0.958. The use of a copolymeric surfactant allows the dilution of the highly concentrated emulsions without any change in the particle size distribution as confirmed by laser diffraction measurements. We found that the polarization technique allows the determination of the film thickness between water drops rather than their sizes. Consequently, we propose a geometrical relationship to determine an average drop size from the film thickness. The sensitivity of this alternative technique to detect changes in average drop size was studied by changing some process and formulation parameters. Drop size determination in highly concentrated emulsions via this method is useful since the measurement protocol neither involves dilution nor induces structural changes in the emulsion.

Journal of Colloid and Interface Science, 2004

The behavior of a commercial sucrose stearate blend has been examined by means of various experim... more The behavior of a commercial sucrose stearate blend has been examined by means of various experimental techniques (differential scanning calorimetry, light polarization and electron microscopy, and rotational rheometry). A partial phase diagram in water has been established. It shows that the binary system forms a lamellar lyotropic mesophase and that the melting behavior is characterized by a lamellar gel-lamellar liquid crystalline phase transition. The identification of the liquid crystalline phase has been carried out from textural observation using polarization microscopy and freeze-fracture electron microscopy. At low surfactant concentrations, the phase transition has been followed through rheological experiments. Furthermore, a shear-induced transition, from the lamellar phase (sheets of surfactant bilayers including a few large multilamellar vesicles) to an onion phase, has been observed above a critical temperature of 43 • C. The vesicles so obtained did not relax over more than 3 weeks. The presence of a small ratio of distearate in the sugar ester blend seems to be the key to vesicle formation at low surface-active material concentration.

Journal of Colloid and Interface Science, 2002

The stability of oil-in-water emulsions prepared using dextran, a natural polysaccharide, hydroph... more The stability of oil-in-water emulsions prepared using dextran, a natural polysaccharide, hydrophobically substituted with phenoxy groups, was studied. The evolution of the emulsion droplet size was investigated as a function of polymer concentration (Cp = 0.2 to 1% w/w in a water phase) and the degree of phenoxy substitution (τ = 4.2 to 15.7%). For the highest τ values, emulsions, which presented submicrometer droplets, were stable over more than 4 months at room temperature. The most substituted polymers clearly showed a better efficiency to lower the surface tension at the oil/water interface. DexP did not induce real viscosification of the continuous phase. The linearity of the particle volume variation with time, and the invariability of the volume distribution function, proved that Ostwald ripening was the main destabilization mechanism of the phenoxy dextran emulsions. The nature of the oil dispersed phase drastically affected the behavior of emulsions. While the emulsions prepared with n-dodecane presented a particle growth with time, only few size variations occurred when n-hexadecane was used. Furthermore, small ratios of n-hexadecane in n-dodecane phase reduced the particle growth due to the lower solubility and lower diffusion coefficient in water of n-hexadecane, which acted as a ripening inhibitor. C 2002 Elsevier Science (USA)

Journal of Colloid and Interface Science, 2006

Surface tension properties of an enzymatically synthesized equimolar mixture of trehalose mono- a... more Surface tension properties of an enzymatically synthesized equimolar mixture of trehalose mono- and didecanoate in aqueous solutions have been determined. At 20 degrees C a critical micellar concentration (CMC) of 50 micromol/l and a minimal surface tension of 28 mN/m have been obtained. Above the CMC, it has been shown that up to a concentration of 42 wt%, and in a 20-60 degrees C temperature range the sugar ester aqueous solutions do not form any crystalline structure, nor present any phase transition, and the trehalose decanoate molecules form an isotropic worm-like micellar phase. The rheological properties indicate however a more complicated picture in the same concentration and temperature ranges. In steady shear, the viscosity of the trehalose decanoate solutions do not exhibit any shear rate dependence from 1 to 100 s(-1) for concentrations up to 42 wt%. Below 0.8 wt%, the viscosity remains constant and close to that of water; then, between 0.8 and 23 wt%, the viscosity shows a quadratic increase with surfactant concentration. For higher concentrations, up to 42 wt%, no further significant increase in viscosity is observed. In oscillatory shear experiments, the solutions exhibit viscoelastic properties. The observed rheological behavior as a function of concentration and temperature may be due to a progressive evolution of the trehalose decanoate molecular associations: as the concentration increases, the system evolves towards an entangled and/or partially branched or cross-linked micellar network, and eventually a multiconnected network of cross-linked micelles.

Journal of Applied Polymer Science, 2002

ABSTRACT The production of porous polymeric particles is attractive for a large number of applica... more ABSTRACT The production of porous polymeric particles is attractive for a large number of applications and can be achieved by various techniques. Although numerous production schemes exist for glassy polymers, difficulties arise for soft, rubbery materials that need a chemical crosslinking step, such as elastomers. This is particularly true for poly(dimethylsiloxane) (PDMS), which shows the lowest glass-transition temperature among the polymers. Recent studies suggest in situ hydrogen bubble formation or vacuum drying of water droplets dispersed in the polymer matrix in order to generate porous PDMS structures. In this work we report early results based on the chemical crosslinking of water in PDMS emulsion droplets in a mechanically stirred thermostated water vessel. This approach is shown to lead to high porosity PDMS beads (ca. 10−3 m particle diameter) with an open structure whose properties (diameter and porosity) are strongly influenced by the starting composition (solvent, surfactant, and polymer types and ratios), as well as the operating parameters (agitation and temperature). The possible uses of these derived beads are discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 967–971, 2002

Industrial & Engineering Chemistry Research, 2003

ABSTRACT The regions corresponding to different emulsion morphology occurrences have been clearly... more ABSTRACT The regions corresponding to different emulsion morphology occurrences have been clearly identified on a bidimensional formulation−composition map. Multiple emulsions spontaneously form when there is a conflict between the formulation and composition effects. In such systems the most external emulsion is found to be unstable when the formulation effect is produced by a single surfactant. The use of a proper surfactant−polymer mixture allows one to strongly inhibit the mass transfer and to considerably lengthen the equilibration between interfaces. As a consequence, the multiple emulsion can be stable enough to be used in encapsulation and controlled-release applications. The area where multiple emulsions occur and their characteristics (conductivity and amount of encapsulated external phase) are reported for a system containing a sorbitan ester lipophilic surfactant and a diblock poly(ethylene oxide)−poly(propylene oxide) hydrophilic polymer, as a function of the formulation and composition, for a single-step process in which a specific amount of mechanical energy is supplied. An increase in the oil viscosity is found to alter the map and to modify the multiple emulsion characteristics. The application of the results to emulsion-making technology is discussed.

Industrial & Engineering Chemistry Research, 2010

ABSTRACT We studied the energy consumption per unit volume during preparation of highly concentra... more ABSTRACT We studied the energy consumption per unit volume during preparation of highly concentrated water-in-oil emulsions in a two-step semibatch process. In particular, we studied the effect of two process variables, the water addition flow rate (Qw) and the agitation speed (N). The oil used for emulsion preparation was n-dodecane, the surfactant was sorbitan monooleate (Span 80) and deionized water was used for the dispersed phase. The results obtained showed that two steps were required to get complete incorporation of the dispersed phase and a homogeneous and stable gel-emulsion. With the help of independent physical characteristics measurement performed at the end of the preparation process, we established two functional relationships, relating storage modulus (G′) with energy consumption (Ev), (G′ Ev0.6), and average liquid cell size (Rm) of the dispersed phase with energy consumption (Ev), (Rm EV−0.3). A structural scaling law can be deduced that relates the elastic modulus to the reciprocal of the square of the average liquid’s cell size of the gel-emulsion, corroborated by independent measurements and predicted by recent published models.

Industrial & Engineering Chemistry Research, 2006

... Lionel Choplin, ‡ and Jean-Louis Salager* †. ... 3, Chapter 2. (4) Salager, JL; Miñana-Perez,... more ... Lionel Choplin, ‡ and Jean-Louis Salager* †. ... 3, Chapter 2. (4) Salager, JL; Miñana-Perez, M.;Perez-Sanchez, M.; Ramirez-Gouveia, M.; Rojas, CI Surfactant−Oil−Water Systems near the Affinity Inversion Part III: The two Kinds of Emulsion Inversion. J. Dispersion Sci. Technol. ...

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011

Poly(ethylene oxide)-covered polystyrene nanoparticles were prepared by free radical miniemulsion... more Poly(ethylene oxide)-covered polystyrene nanoparticles were prepared by free radical miniemulsion polymerization after using an original low energy emulsification procedure called Near-PIT method. This procedure consisted in heating the initial monomer emulsion up to a temperature close to the phase inversion temperature (PIT) but lower. The surfactants used were commercial Brij® 78 and Brij® 700 and mixtures of both. The Near-PIT

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2006

When the emulsion inversion from abnormal to normal morphology is induced by continuous stirring ... more When the emulsion inversion from abnormal to normal morphology is induced by continuous stirring only, it takes place through the formation of a multiple emulsion in which the external phase is continuously included as droplets in the dispersed phase drops. In the studied case the system exhibits an initial O/W morphology, then a w/O/W multiple one before inverting into a W/O emulsion. The general trend reported in the literature is that the higher the initial water content, the longer the incorporating process to swell the drops in order to attain the critical dispersed phase volume that triggers inversion. The present study reports, for nonionic systems with a given hydrophilic-lipophilic balance (HLB = 6) and 7 wt.% of surfactant concentration, that this trend is found to be unexpectedly reversed when the initial water content increases beyond 80%. This anomalous result is attributed to an indirect increase in the lipophilicity of the formulation due to the variation of the interfacial surfactant mixture with the water/oil ratio, and to the formation of liquid crystals at high water contents.

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011

Oil-in-water nanoemulsions were prepared with mixtures of a non-ionic surfactant and an amphiphil... more Oil-in-water nanoemulsions were prepared with mixtures of a non-ionic surfactant and an amphiphilic anionic polyelectrolyte (HMPA1). Initial droplet diameters and ageing rates of emulsions were investigated as a function of various formulation and storage parameters (storage temperature, nature and amount of oil and stabilizers). The main ageing process was identified as Ostwald ripening, at least within the first weeks. Emulsion

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2002

Oil-in-water emulsions were prepared using dextran, a natural polysaccharide, hydrophobically mod... more Oil-in-water emulsions were prepared using dextran, a natural polysaccharide, hydrophobically modified with phenoxy groups. Emulsions were prepared by two different processes which were sonication and microfluidization. The average diameter of oil droplets and the stability with time of the resulting emulsions were investigated as a function of polymer concentration (Cp0/0.1 Á/1% w/w in water phase) and the degree of polymer grafting (t0/4.2 Á/15.7%). The microfluidization process allowed to realize emulsions with lower initial particle size than the sonication method. For the highest degrees of grafting and for Cp values ]/0.2% w/w, submicronic emulsions were obtained, which were stable for more than 4 months at room temperature. Interfacial measurements at the n-dodecane/water interface clearly showed a better efficiency of the most substituted polymers to lower the surface tension. #

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1999

Liquid fluorocarbons with high gas-dissolving capacity, high fluidity, low surface tension, excep... more Liquid fluorocarbons with high gas-dissolving capacity, high fluidity, low surface tension, exceptional biological inertness, are in clinical trials for the treatment of acute respiratory failure by liquid ventilation. Fluorocarbons are able to reopen collapsed alveoli and facilitate the exchange of the respiratory gases. They also constitute a promising carrier for administration of drugs via the pulmonary route. Since pharmaceuticals are usually not soluble in fluorocarbons, we have designed and prepared reverse water-in-fluorocarbon emulsions. These emulsions are stabilized by perfluoroalkylated surfactants with a dimorpholinophosphate head group. They can be sterilized by heat or filtration through a 0.22 mm membrane, and are stable (initial mean droplet diameter = 0.17 mm, 0.26 mm after 1 year at 25°C). Various drugs, including antibiotics, vasodilators and anticancer agents, were incorporated in the aqueous phase of the emulsions. Preliminary biocompatibilty tests are encouraging. An in 6itro study at 37°C of the release of 5,6-carboxyfluorescein encapsulated in the internal phase of a reverse water-in-perfluorooctyl bromide emulsion was significantly slower than for a reverse water-in-octyl bromide emulsion (4% vs 37% of release after 6 h) or for a standard isopropyl myristate reverse emulsion stabilized by Span 80 (48% after 6 h). This is assigned to the extreme hydrophobic character of fluorocarbons which act as a physical barrier to diffusion of encapsulated hydrophilic compounds.