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Preparation and characterisation of pheroid vesicles / Charlene Ethel UysUys, Charlene Ethel January 2006 (has links)
Pheroid is a patented system comprising of a unique submicron emulsion type
formulation. Pheroid vesicles consist mainly of plant and essential fatty acids and
can entrap, transport and deliver pharmacologically active compounds and other
useful molecules. The aim of this study was to show that a modulation of
components and parameters is necessary to obtain the optimum formula to be used
in pharmaceutical preparations.
Non-optimal or non-predictable stability properties of emulsions can be limiting for the
applications of emulsions (Bjerregaard et al., 2001:23). Careful consideration was
given to the apparatus used during the processing along with the ratios of the various
components added to the formulation and the storage conditions of the Pheroid
vesicles.
A preliminary study was performed to optimize the most accurate processing
parameters during emulsification. The effect of emulsification rate and time, the
temperature of the aqueous phase, the number of days the water phase were
gassed, the concentration of the surfactant, cremophor® RH 40, used and the
concentration of Vitamin F Ethyl Ester CLR added to the oil phase of the o/w
emulsion has been studied. Quantification of the mean particle size, zeta potential,
turbidity, pH and current values were used to characterize the emulsions. The
samples were characterised after 1, 2, 3, 7, 14, 21 and 28 days of storage. The
emulsions were also characterised with confocal laser scanning microscopy (CLSM)
to measure the number and size and size distribution of the vesicles.
After determination of the processing variables influencing the emulsion stability an
accelerated stability test was conducted on a final formula. In the present study,
accelerated stability testing employing elevated temperatures and relative humidity
were used with good accuracy to predict long-term stability of an o/w emulsion kept
at both 5 and 25 OC with 60 % relative humidity and 40 OC with 75 % relative
humidity. The results of the stability tests were presented in histograms of the
physical properties 24 hours, 1 month, 2 months and 3 months after preparation of
the emulsion.
It was concluded that Pheroid vesicles demonstrate much potential as a drug delivery
system. The high stability of this formula allows its use in a wide variety of
applications in the pharmaceutical industry. / Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2007.
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Preparation and characterisation of pheroid vesicles / Charlene Ethel UysUys, Charlene Ethel January 2006 (has links)
Pheroid is a patented system comprising of a unique submicron emulsion type
formulation. Pheroid vesicles consist mainly of plant and essential fatty acids and
can entrap, transport and deliver pharmacologically active compounds and other
useful molecules. The aim of this study was to show that a modulation of
components and parameters is necessary to obtain the optimum formula to be used
in pharmaceutical preparations.
Non-optimal or non-predictable stability properties of emulsions can be limiting for the
applications of emulsions (Bjerregaard et al., 2001:23). Careful consideration was
given to the apparatus used during the processing along with the ratios of the various
components added to the formulation and the storage conditions of the Pheroid
vesicles.
A preliminary study was performed to optimize the most accurate processing
parameters during emulsification. The effect of emulsification rate and time, the
temperature of the aqueous phase, the number of days the water phase were
gassed, the concentration of the surfactant, cremophor® RH 40, used and the
concentration of Vitamin F Ethyl Ester CLR added to the oil phase of the o/w
emulsion has been studied. Quantification of the mean particle size, zeta potential,
turbidity, pH and current values were used to characterize the emulsions. The
samples were characterised after 1, 2, 3, 7, 14, 21 and 28 days of storage. The
emulsions were also characterised with confocal laser scanning microscopy (CLSM)
to measure the number and size and size distribution of the vesicles.
After determination of the processing variables influencing the emulsion stability an
accelerated stability test was conducted on a final formula. In the present study,
accelerated stability testing employing elevated temperatures and relative humidity
were used with good accuracy to predict long-term stability of an o/w emulsion kept
at both 5 and 25 OC with 60 % relative humidity and 40 OC with 75 % relative
humidity. The results of the stability tests were presented in histograms of the
physical properties 24 hours, 1 month, 2 months and 3 months after preparation of
the emulsion.
It was concluded that Pheroid vesicles demonstrate much potential as a drug delivery
system. The high stability of this formula allows its use in a wide variety of
applications in the pharmaceutical industry. / Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2007.
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Characterizations of oil-in-water (O/W) emulsions containing different types of milk fats prepared using rhamnolipids as emulsifiers : [a thesis presented in partial fulfillment of the requirements for the degree of Master of Technology in Food Technology at Massey University, Auckland, New Zealand] EMBARGOED UNTIL 1 MARCH 2011Lin, Lu January 2009 (has links)
Emulsions containing three different types of milk fat fractions (MF13, MF27 and MF42) and anhydrous milk fat (AMF) were prepared at oil to water (O/W) ratios of 1:9, 3:7, 5:5 and 7:3 using rhamnolipids as emulsifiers. The prepared emulsions were analyzed for their storage stability and properties (colour, particle size, zeta potential and rheology). The effects of various factors (freezing/thawing, heating, pH, salts and ionic strength) on the stability of emulsions were also investigated. All emulsions prepared with an O/W ratio of 7:3, regardless of the type of milk fat, rendered a highly condensed, semi solid and cream-like substance whereas other emulsions containing less oil were in a liquid form. Among the four different O/W ratios tested, the highest emulsion stability during the storage of 12 weeks was observed from the emulsions containing 1:9 O/W ratios, due to a combine effect of smaller emulsion particle size and lower collision frequency between droplets. Interestingly, the emulsions with 7:3 O/W ratios were found to be more stable than the ones with 5:5 O/W ratios. This might be due to the limited movements of closely-packed emulsion droplets induced by the high oil concentration of 7:3 O/W ratios. The emulsion stability was significantly affected by low pH, especially at lower than pH 4, due to the loss of electrostatic repulsions between droplets leading to droplet coalescence and also possibly due to hydrolysis of rhamnolipid molecules. The presence of salts (NaCl, KCl and CaCl2) also rendered the emulsion unstable. The degree of instability was gradually increased with increasing salt concentrations. CaCl2 had the most significant effect even at a very low concentration. The viscosity of emulsions increased with increasing oil concentration but was not affected by the types of milk fats. Emulsions with 3:7, 5:5 and 7:3 O/W ratios exhibited non-Newtonian and shear thinning flow behaviour. At 7:3 O/W ratios, MF13 exhibited gel-like properties whereas both MF42 and AMF emulsions became more solid-like at higher frequency.
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Effect of surfactant structure on properties of oil/water interfaces : A coarse-grained molecular simulation study.Rekvig, Live January 2004 (has links)
<p>The elastic properties of oil/water/surfactant interfaces play an important role in the phase behaviour of microemulsions and for the stability of macroemulsions. The aim of this thesis is to obtain an understanding of the relationship between the structure of the surfactant molecules, the structure of the interface, and macroscopic interfacial properties. To achieve this aim, we performed molecular simulations of oil/water/surfactant systems. We made a quantitative comparison of various model surfactants to determine how structural changes affect interfacial properties and film rupture. The model consists of water, oil, head, and tail beads, and surfactants are constructed by coupling head and tail beads with harmonic springs. We used a hybrid dissipative particle dynamics-Monte Carlo scheme. The former was used to simulate particle trajectories and the Monte Carlo scheme was used to mimic experimental conditions: bulk-interface phase equilibrium, tensionless interfaces in microemulsions, and the surface force apparatus.</p><p>A detailed comparison of various non-ionic model surfactants showed how structural changes affect interfacial properties:</p><p>Comparison between linear and branched surfactants showed that the efficiency of adsorption is higher for linear surfactants, although branched surfactants are more efficient at a given surface density. Linear surfactants can be more efficient also at the same surface density if the head group is sufficiently soluble in oil, because low head-oil repulsion makes the branched isomers stagger at the interface. The bending rigidity is higher for linear surfactants. Furthermore, branched surfactants make oil droplets coalesce more easily than linear surfactants do, but linear and branched surfactants have roughly the same effect on water droplet coalescence. </p><p>Comparison of linear surfactants with varying chain lengths showed that longer surfactants have a lower surface tension and higher bending rigidity. The increase in rigidity with chain length follows a power law, but the exponent is higher for surfactant monolayers at a fixed density than at a fixed tension. Longer tails and/or denser monolayers influence the stability of water droplets in a positive direction, and the stability of oil droplets in a negative direction. </p><p>Addition of cosurfactant showed that mixed monolayers have a lower bending rigidity than pure monolayers at the same average chain length and tension. Cosurfactants have a negative effect on the stability of water droplets, and a positive effect on the stability of oil droplets.</p> / Paper I reprinted with kind permission of EDP Sciences. Paper III reprinted with kind permission of the American Institute of Physics. Paper IV reprinted with kind permission of the American Physics Society.
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Effect of surfactant structure on properties of oil/water interfaces : A coarse-grained molecular simulation study.Rekvig, Live January 2004 (has links)
The elastic properties of oil/water/surfactant interfaces play an important role in the phase behaviour of microemulsions and for the stability of macroemulsions. The aim of this thesis is to obtain an understanding of the relationship between the structure of the surfactant molecules, the structure of the interface, and macroscopic interfacial properties. To achieve this aim, we performed molecular simulations of oil/water/surfactant systems. We made a quantitative comparison of various model surfactants to determine how structural changes affect interfacial properties and film rupture. The model consists of water, oil, head, and tail beads, and surfactants are constructed by coupling head and tail beads with harmonic springs. We used a hybrid dissipative particle dynamics-Monte Carlo scheme. The former was used to simulate particle trajectories and the Monte Carlo scheme was used to mimic experimental conditions: bulk-interface phase equilibrium, tensionless interfaces in microemulsions, and the surface force apparatus. A detailed comparison of various non-ionic model surfactants showed how structural changes affect interfacial properties: Comparison between linear and branched surfactants showed that the efficiency of adsorption is higher for linear surfactants, although branched surfactants are more efficient at a given surface density. Linear surfactants can be more efficient also at the same surface density if the head group is sufficiently soluble in oil, because low head-oil repulsion makes the branched isomers stagger at the interface. The bending rigidity is higher for linear surfactants. Furthermore, branched surfactants make oil droplets coalesce more easily than linear surfactants do, but linear and branched surfactants have roughly the same effect on water droplet coalescence. Comparison of linear surfactants with varying chain lengths showed that longer surfactants have a lower surface tension and higher bending rigidity. The increase in rigidity with chain length follows a power law, but the exponent is higher for surfactant monolayers at a fixed density than at a fixed tension. Longer tails and/or denser monolayers influence the stability of water droplets in a positive direction, and the stability of oil droplets in a negative direction. Addition of cosurfactant showed that mixed monolayers have a lower bending rigidity than pure monolayers at the same average chain length and tension. Cosurfactants have a negative effect on the stability of water droplets, and a positive effect on the stability of oil droplets. / Paper I reprinted with kind permission of EDP Sciences. Paper III reprinted with kind permission of the American Institute of Physics. Paper IV reprinted with kind permission of the American Physics Society.
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Synthesis And Charaterization Of Multi-hollow Opaque Polymer PigmetsAsmaoglu, Serdar 01 July 2012 (has links) (PDF)
In the present work, a new generation opaque polymer pigment with multihollow structure was synthesized by suspension polymerization of &ldquo / Water-in-Oil-in-Water&rdquo / (W/O/W) emulsion system. Oil phase was methyl methacrylate and ethylene glycol dimethacrylate monomer mixture at 1:1 weight ratio. The dimension and distribution of hollows inside polymer particles are dependent on the size of water droplets which are encapsulated in micelles. For Water-in-Oil (W/O) assembly, a hydrophobic surfactant and hydrophilic co-surfactant (Span 80-Tween 80) combination with a hydrophilic/lipophilic balance (HLB) value between 5-8 was used. The effects of surfactant and co-surfactant composition on the stability of the W/O emulsion and also on the size of water droplets were studied. In addition, the effect of the ultrasonication on the average size of water droplets was investigated.
The hollow size distribution which may possibly give the maximum scattering efficiency was predicted by a mathematical model based on the Mie scattering. The optimum size
distribution for W/O emulsion was obtained at the monomer/surfactant/water ratio of 75.5/9.4/15.1 after ultrasonication for 30 seconds at 80 W power.
The W/O/W emulsion was prepared by dispersing the W/O emulsion in aqueous solution of hydrophilic Triton X-405. The influence of surfactant concentration and mechanical mixing on monomer droplets was investigated by size measurement and optical microscopy. After stabilizing with 1 %w/w polyvinylpyrrolidone (PVP) solution, the W/O/W emulsion was polymerized at 55 ° / C for 20 h. The surface morphology of synthesized polymer pigments was analyzed by scanning electron microscopy (SEM) and the inner hollow structure was confirmed by transmission electron microscopy (TEM). The analysis indicated that multihollow opaque polymer pigments were successfully synthesized.
The opacity, the L*a*b* color, and the gloss properties of polymer pigments were examined by spectrophotometer and glossmeter. The opacity values were assessed by contrast ratio measurements, and the synthesized polymer pigments provided up to 97.3 % opacity (50 %v/v solid content). In addition, the pigments exhibited low gloss values, and yielded matt films.
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Desenvolvimento de sistemas farmac?uticos emulsionados para veicula??o g?nicaVer?ssimo, Lourena Mafra 26 February 2007 (has links)
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Previous issue date: 2007-02-26 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Broadly speaking, the concept of gene therapy involves the transfer of a genetic material into a cell, tissue, or organ in order to cure a disease or at least improve the clinical status of a patient. Making it simple, gene therapy consists in the insertion of functional genes into cells containing defective genes by substituting, complementing or inhibiting them. The achievement of a foreigner DNA expression into a population of cells requires its transfer to the target. Therefore, it is a key issue to create systems able to transfer and protect the DNA until it reaches the target, the vectors. The disadvantages related to the use of viral vectors have encouraged efforts to develop emulsions as non-viral vectors. In fact, they are easily produced, present controllable stability and enable transfection. The aim of this work was to develop an emulsion for gene therapy and evaluate its ability to compact nucleic acids by the development of a complex with the plasmid pIRES2-EGFP. The first step was to determine the Hydrophilic Lipophilic Balance (HLB) of the Captex? 355 (oily internal phase of the emulsion) through long and short term stability assays. Based on the results, emulsions composed of Captex? 355, Tween 20? and Span 60? with 10.7 HLB were produced by three different methods: phase inversion, spontaneous emulsification and sonication. The results showed that the lowest diameter and best stability of the emulsions were achieved by the sonication method. The cationic emulsions were made by adding DOTAP to the basic emulsion. Its association with pIRES2-EGFP was evaluated by electrophoresis. Several rates of emulsion and DNA were evaluated and the results showed that 100% of the complex was formed when the rate DOTAP/DNA(nmol/?g) was 130. In conclusion, the overall results show the ability of the proposed emulsion to compact pIRES2-EGFP, which is a requirement to a successful transfection. Therefore, such formulation may be considered a promising candidate for gene therapy / Terapia g?nica, em uma ampla defini??o, ? o tratamento de doen?as baseado na transfer?ncia de material gen?tico a uma c?lula, tecido ou ?rg?o com o intuito de curar ou melhorar o estado cl?nico do paciente. Em sua forma mais simples, a terapia g?nica consiste na inser??o de genes funcionais em c?lulas com genes defeituosos objetivando substituir, complementar ou inibir esses genes causadores de doen?as. Para que o DNA ex?geno seja expresso em uma popula??o celular faz-se necess?ria a sua transfer?ncia at? o local. Assim, ? necess?rio criar ve?culos, os vetores, que transportem e protejam o DNA at? que este chegue a uma popula??o celular alvo. Os obst?culos encontrados com a utiliza??o de vetores virais t?m proporcionado o interesse no desenvolvimento de emuls?es cati?nicas como vetores n?o-virais, por serem f?ceis de produzir, apresentarem estabilidade control?vel e facilitarem a transfec??o g?nica. O objetivo deste trabalho foi desenvolver um sistema emulsionado para terapia g?nica e avaliar sua capacidade de compacta??o de ?cidos nucl?icos atrav?s da sua associa??o com o plasm?deo pIRES2-EGFP. Primeiramente o EHLc do TCM utilizado, o Captex? 355, foi determinado atrav?s de ensaios de estabilidade acelerada e a longo termo. Com base nos resultados obtidos, emuls?es de EHL 10,7 compostas de Captex? 355, Tween 20? e Span 60? foram preparadas pelos m?todos de invers?o de fases, emulsifica??o espont?nea e sonica??o e elegeu-se o melhor m?todo para o preparo das emuls?es cati?nicas. As emuls?es de menor granulometria e maior estabilidade foram obtidas atrav?s do m?todo de sonica??o. As emuls?es cati?nicas foram preparadas acrescendo-se ? emuls?o base o DOTAP e a sua associa??o com o pIRES2-EGFP foi avaliada atrav?s da t?cnica de eletroforese em gel de agarose. V?rias propor??es de emuls?o e DNA foram testadas e os resultados demonstraram que houve forma??o de 100% dos complexos quando a propor??o DOTAP/DNA(nmol/?g) foi igual a 130. Em conclus?o, o conjunto dos resultados obtidos demonstra a capacidade da emuls?o proposta neste trabalho de compactar o DNA, requisito necess?rio para uma boa transfec??o, tornando a formula??o uma forte candidata ? utiliza??o em terapia g?nica
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Relating the Formation Mechanisms and Kinetic Stability of Complex Shipboard Emulsions to the Physical and Chemical Properties of Model Surfactant-Oil-Water-Salt SystemsCole R Davis (11113473) 22 July 2021 (has links)
<p>Emulsions are advantageous
in many applications including healthcare, food science, and detergency due to
their ability to disperse one fluid in another, otherwise immiscible fluid. For
the same reason, emulsions are also problematic when mixtures of oil and water
are undesirable like in industrial wastewater pollution and fuel systems. Whether
an emulsion is desirable or not, both benefit from understanding the
fundamental relationship of emulsion formation and stability to the physical
and chemical properties of the oil-water-surfactant mixture. This work
identifies the formation and stability mechanisms of model emulsion systems
through the perspective of emulsion prevention for applications in shipboard
wastewater (bilge water) treatment. Although experiments in this study were
designed to model bilge water systems, their fundamental approach makes them
practical for many different applications like food science, pharmaceuticals,
and detergency.</p>
<p>The impact of salts on
emulsion formation and stability to coalescence were studied to understand how
emulsions stabilized by ionic surfactant behave in saltwater environments. Droplet
size analysis revealed that emulsion stability to coalescence improved with
salt concentration. Through interfacial tension and zeta potential
measurements, it was found that the addition of salt promoted close surfactant
packing and faster surfactant adsorption kinetics at the oil-water interface.
This aided in preventing coalescence and created conditions favorable for the
formation of a stable Newton black film. Extended DLVO calculations were used
to model the interaction energy between droplets and suggested that hydration
forces play an important role in stabilizing these systems. These emulsions
were then studied under dynamic ageing conditions to observe the impact of
motion on emulsion stability. While statically aged emulsions were stable to
coalescence, dynamic ageing induced coalescence (increased droplet size) or
emulsified the oil droplets (decreased droplet size) depending on the
surfactant concentration and energy input during ageing.</p>
Formation mechanisms
and stability of spontaneous emulsion systems were also investigated. Low
molecular weight oils (e.g., toluene, xylenes, and cyclohexane) were found to
spontaneously emulsify with nonylphenol polyethoxylated (NPE) and sodium dodecylbenzene
sulfonate (SDBS). NPE emulsions spontaneously emulsified via diffusion and
micelle swelling and displayed limited stability due to Ostwald ripening. SDBS
emulsions also spontaneously emulsified with toluene but only in saltwater
environments. As the concentration of salt in the aqueous phase increased, the
spontaneity of these emulsions also increased. These systems were analyzed
using the hydrophilic lipophilic difference (HLD) theory to evaluate its efficacy
for predicting the conditions favorable for spontaneous emulsification.
Limitations and practicality of using the HLD model for these systems were also
explored.
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Medical White Oil in Cosmetic Applications / Medicinsk Vitolja i kosmetikaDubeck Schömer, Hanna January 2021 (has links)
Fuktbevarare är de produkter som oftast skrivs och rekommenderas av dermatologer, och den vanligaste typen av fuktgivare är lotioner och krämer. Dessa produkter är emulsioner, vilka ofta innehåller medicinsk vit olja (MWO) på grund av deras skyddande egenskaper samt enastående hudkompabilitet. Traditionellt så har de MWO som används varit parafinska. Då naftenoljor ofta har visat sig ha bättre emulsions stabilitet, har detta examensarbete ämnat attjämföra emulsions stabiliteten för Nynas ABs nya MWO, N-MWO, med en parafinsk motsvarighet, P-MWO. Jämförelsen av de två oljorna genomfördes genom att variera följande faktorer: olje- och emulgator typ, koncentration av emulgator samt både med och utan parfym. De två emulgator system som användes bestod av Promulgen D (en kommersiell produkt från Lubrizol) samt kombinationen av Tween 80 och Span 20. Bättre emulsionsstabilitet och mindre droppstorlek och fördelning utficks då högre koncentration Promulgen D användes. En högre koncentration av Tween 80 och Span 20 gav dock inte samma gynnsamma effekt. Resultaten från samtliga tester påvisade att emulsions stabiliteten inte påverkades utav parfym. Det som istället gav störst påverkan var typ av emulgator. De prover som innehöll P-MWO samt Tween 80 och Span 20 fasseparerade. Detta berodde dock troligen mer på att P-MWO inte var kompatibel med dessa emulgatorer eftersom oljetypen inte påverkade emulsionsstabiliteten när Promulgen D användes som emulgator. / Moisturizers are the most prescribed products in dermatology, and the most common type of moisturizer delivery systems are lotions and creams. These are emulsions and often contain medical white oil (MWO) due to their protective properties and excellent skin compatibility. The MWO used in cosmetics have traditionally been paraffinic. However, as naphthenic oils often have been proven to create better emulsion stability, this thesis aimed to compare Nynas AB's new MWO, N-MWO, with a paraffinic oil, P-MWO, with similar properties regarding their emulsion stability. The two oils were compared by analyzing their emulsion stability using a rheometer and a Mastersizer 3000 while varying the following factors: type of oil, type of emulsifier, emulsifier concentration, and with and without perfume. The two emulsifying systems used were the commercial product Promulgen D from Lubrizol and the combination of Tween 80 and Span 20. Better emulsion stability and smaller droplet size distribution were obtained when a higher content of Promulgen D was added. However, a higher concentration of Tween 80 and Span 20 did not have the same favorable effect. The results showed that the addition of perfume had no effect, while the type of emulsifier influenced the emulsion stability the most. The samples made from Supela 240 and Tween 80 and Span 20 phase separated. This was more likely due to P-MWOs incompatibility with these emulsifiers as oil type did not influence the emulsion stability when Promulgen D was used as an emulsifier.
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[pt] EFEITO DA REOLOGIA INTERFACIAL NA ESTABILIDADE DE EMULSÕES ÁGUA-ÓLEO / [en] EFFECT OF INTERFACIAL RHEOLOGY ON THE STABILITY OF WATER-OIL EMULSIONTALITA COFFLER BOTTI BRAZ 29 September 2022 (has links)
[pt] Inúmeros estudos têm sido realizados para melhor entender a formação
e estabilidade de emulsões. Em algumas situações, é desejável ter emulsões
estáveis; em outros, a separação de fases por coalescência de gotas é benéfica. Em ambos os casos, é importante entender os mecanismos associados
ao processo de coalescência. O presente trabalho investiga a relação entre
as propriedades reológicas das interfaces óleo-água e o tempo de drenagem
de um filme fino de óleo entre duas gotas aquosas. A tensão interfacial e
a reologia dilatacional interfacial foram medidas usando a análise axissimétrica da forma da gota. Foram avaliadas diferentes concentrações de um
tensoativo não iônico (Span 80) dissolvido em óleo mineral (Primol 352).
Os resultados indicam uma relação direta entre as propriedades da estrutura formada na interface óleo-água e a ausência de coalescência das gotas.
Para concentrações de surfactante abaixo da concentração micelar crítica
(CMC), a interface é fracamente elástica (fluid-like) e o processo de coalescência sempre ocorre; o tempo de drenagem não está relacionado ao tempo
de envelhecimento da interface. Para concentrações de surfactante acima
da CMC, os módulos elástico e viscoso mostraram mudanças significativas
com o envelhecimento, levando à formação de um filme sólido na interface,
impedindo a coalescência entre as gotas. Usamos experimentos de coalescência gota/gota para avaliar o efeito da reologia interfacial na dinâmica
de coalescência. Para entender melhor o fenômeno da não coalescência, estudamos microscopicamente a estrutura do filme interfacial e observamos
o aparecimento de pequenas gotas de água formadas na interface através
de emulsificação espontânea. Descobrimos que a taxa de surgimento dessas
microgotículas está diretamente relacionada à concentração de surfactante.
À medida que a concentração de surfactante aumenta, mais rápido ocorre
o processo de emulsificação espontânea, o que confirma os resultados obtidos com a reologia interfacial. Finalmente, um novo método para promover
a desestabilização da emulsão impondo uma perturbação do filme interfacial pelo escoamento das gotas através de capilares constritos é proposto e
testado. / [en] Several studies have been conducted to understand emulsions formation and stability. In some situations, it is desirable to have stable emulsions;
in others, phase separation through drop coalescence is beneficial. In both
cases, it is important to understand the mechanisms associated to the coalescence process. The present work investigates the relationship between
rheological properties of oil-water interfaces and the drainage time of a thin
oil film between two aqueous drops. Interfacial tension and dilatational rheology were measured using the axisymmetric drop shape analysis. We evaluated different concentrations of a nonionic surfactant (Span 80) dissolved
in mineral oil (Primol 352) phase. The results indicate a direct relationship
between the properties of the structure formed at the oil-water interface and
the absence of droplet coalescence. For low surfactant concentrations, below the critical micelle concentration (CMC), the interface is weakly elastic
(fluid-like) and the coalescence process always occurs; the draining time is
not to related to the aging time of the interface. For surfactant concentrations above CMC, the elastic and viscous moduli showed significant changes
with aging leading to the formation of a solid-like film at the interface preventing further coalescence. We used a drop/drop coalescence experiments
to evaluate the effect of interfacial rheology on the coalescence dynamics. To
better understand the phenomenon of non-coalescence, we study the structure of interfacial film microscopically and observe the appearance of small
water droplets formed at the interface by spontaneous emulsification. We
found that the emergence rate of these microdroplets is directly related to
the surfactant concentration. As the surfactant concentration increases, faster the spontaneous emulsification process occurs, which confirms the results
obtained with the interfacial rheology. Finally, a new method to promote
emulsion destabilization by imposing a perturbation of the interfacial film
by flowing the drops through constricted capillaries is proposed and tested.
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