Spelling suggestions: "subject:"[een] EMULSION DESTABILIZATION"" "subject:"[enn] EMULSION DESTABILIZATION""
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Studium stability emulzí pomocí fyzikálně-chemických a optických metod / Study of emulsion stability by means of physical-chemical and optical methodsKuchyňová, Jitka January 2011 (has links)
The diploma thesis deals with the stability determination of model O/W (30/70) emulsions at 25°C. In fact, the time and emulsifier concentration (Tego Care PS) dependences of physical properties (aging) were monitored. In the second part of the work, the influence of conservant on emulsion stabilities were studied. In order to study physical properties of emusions rheometry, differential scanning calorimetry (DSC) and optical microscopy were employed. The rheological measurement provided information on viscosity and viscoelastic modulus. DSC experiments used the repeated freezing/thawing cycles which allowed monitoring of changes in crystallization temperature of water present in emulsions and melting enthalpy of ice formed during the cooling. The optical microscopy was used to examine the change in oil droplet size in the course of emulsion destabilization and phase separation. In this case the image analysis was carried out using program HarFA. The results showed that due to the emulsion creaming, the oil droplets diffuse and aggregate which causes phase separation. Those processes were quickest for the emulsion with lowest emulsifier concentration 0.1 % (destabilization during 51 days) The emulsions with emulsifier concentration about 1.5 and 1.3 % were stable at least for 4 months. The presence of the coemulsifiers increased the elastic modulus and descreased the phase difference due to the network formation. It was shown that for the stability determination is necessary to use conservant due to risk of microbial contamination. DSC experiments allowed to distingush samples prepared under different conditions. Lower rotational speed during emulsion preparation caused the appearance of two melting and crystalization peaks while for higher speed only one peak was observed.
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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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