Interfacial equation of state for ionized surfactants at oil/water interfaces

Bahramian, Alireza; Zarbakhsh, Ali

doi:10.1039/c5sm01406a

Cited by 14 publications

(14 citation statements)

References 31 publications

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“…While the textbooks and review articles also show the surfactants and co-surfactants forming a monolayer at the surfaces of the oil droplets in a cream, we show here that this interfacial layer is very diffuse, suggesting that it is significantly roughened, with the constituent molecules not aligned but staggered. Again, this is entirely consistent with the observations made by Zarbakhsh et al 22,39,40,42,43 wherein the surfactant and lipid layers that form at oil-water interfaces are shown to exhibit a pronounced roughening which cannot be explained simply by thermal broadening and is considered to arise instead because of a staggering of the molecules' hydrocarbon chains brought about by their dissolution within the oil and the resultant disruption of their side-by-side packing.…”

Section: Discussionsupporting

confidence: 90%

Revealing the Hidden Details of Nanostructure in a Pharmaceutical Cream

Ahmadi

Mahmoudi

et al. 2020

Sci Rep

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Creams are multi-component semi-solid emulsions that find widespread utility across a wide range of pharmaceutical, cosmetic, and personal care products, and they also feature prominently in veterinary preparations and processed foodstuffs. The internal architectures of these systems, however, have to date been inferred largely through macroscopic and/or indirect experimental observations and so they are not well-characterized at the molecular level. Moreover, while their long-term stability and shelflife, and their aesthetics and functional utility are critically dependent upon their molecular structure, there is no real understanding yet of the structural mechanisms that underlie the potential destabilizing effects of additives like drugs, anti-oxidants or preservatives, and no structure-based rationale to guide product formulation. In the research reported here we sought to address these deficiencies, making particular use of small-angle neutron scattering and exploiting the device of H/D contrast variation, with complementary studies also performed using bright-field and polarised light microscopy, smallangle and wide-angle X-ray scattering, and steady-state shear rheology measurements. through the convolved findings from these studies we have secured a finely detailed picture of the molecular structure of creams based on Aqueous Cream BP, and our findings reveal that the structure is quite different from the generic picture of cream structure that is widely accepted and reproduced in textbooks. Oil-in-water creams are widely used in pharmaceutical products formulated to treat conditions like atopic dermatitis, rosacea and psoriasis 1. They also form the basis of veterinary medications used to assist wound-healing and treat skin infections 2 , and they are the basis too of a great many personal care products, spanning make-up foundations, anti-perspirants, sun lotions and deodorants 3. All such products are complex, multi-component colloids in which the constituent oil and water phases are stabilised through the addition of one or more ionic, non-ionic or zwitterionic surfactants, in combination with one or more co-surfactants (sometimes referred to as consistency enhancers) which might be long chain fatty acids, fatty alcohols or monoglycerides 4,5. Other components which might be added include humectants such as propylene glycol, anti-oxidants like α-tocopherol acetate, and preservatives like phenoxyethanol 6. The molecular architecture of any given cream formulation will clearly vary according to its chemical composition, and this in turn will determine its chemical and physical stability, and also impact the cream's sensory aesthetics and efficacy as a cosmetic, pharmaceutical, or veterinary product. Despite much research into the properties of creams and their many years of use, however, our understanding of their internal molecular structure is still far from complete, with the unavoidable consequence, therefore, that they are still formulated only in a semi-empirical manner. Junginger and co-workers 7 ...

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Section: Discussionsupporting

confidence: 90%

Revealing the Hidden Details of Nanostructure in a Pharmaceutical Cream

Ahmadi

Mahmoudi

et al. 2020

Sci Rep

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“…As shown in Fig. 5b , SDS solution has lower IFTs in the salt solutions, as it is the characteristic of ionic surfactant systems 35 – 37 . The impact of nanoparticles on the interfacial tension of the surfactant solution weakens in the presence of NaCl and it completely vanishes at high concentrations.…”

Section: Resultsmentioning

confidence: 81%

“…6a and b ). The addition of electrolyte promotes the surfactant activity coefficient and accordingly increases its surface activity 35 , 38 (Fig. 6c ).…”

Section: Resultsmentioning

confidence: 97%

The Role of Electrostatic Repulsion on Increasing Surface Activity of Anionic Surfactants in the Presence of Hydrophilic Silica Nanoparticles

Vatanparast

Shahabi

Bahramian

et al. 2018

Sci Rep

Self Cite

108

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Hydrophilic silica nanoparticles alone are not surface active. They, however, develop a strong electrostatic interaction with ionic surfactants and consequently affect their surface behavior. We report the interfacial behavior of n-heptane/anionic-surfactant-solutions in the presence of hydrophilic silica nanoparticles. The surfactants are sodium dodecyl sulfate (SDS) and dodecyl benzene sulfonic acid (DBSA), and the diameters of the used particles are 9 and 30 nm. Using experimental tensiometry, we show that nanoparticles retain their non-surface-active nature in the presence of surfactants and the surface activity of surfactant directly increases with the concentration of nanoparticles. This fact was attributed to the electrostatic repulsive interaction between the negatively charged nanoparticles and the anionic surfactant molecules. The role of electrostatic repulsion on increasing surface activity of the surfactant has been discussed. Further investigations have been performed for screening the double layer charge of the nanoparticles in the presence of salt. Moreover, the hydrolysis of SDS molecules in the presence of silica nanoparticles and the interaction of nanoparticles with SDS inherent impurities have been studied. According to our experimental observations, silica nanoparticles alleviate the effects of dodecanol, formed by SDS hydrolysis, on the interfacial properties of SDS solution.

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“…Several researchers analyzed adsorption to liquid–liquid interfaces by relating the profile of the IFT curve and the equilibrium tension to relaxation phenomena and surface excess concentration or coverage of adsorbents. The great number of adsorption isotherms and equations of state for surfactants alone demonstrate the divergent behavior of IFT to adsorption. − For nanoparticles without surfactants, Du et al showed that the adsorption energies of individual particles to the oil–water interface can be treated as additive to the overall interfacial energy of the bare interface by assuming that no interactions occur between interfacially adsorbed particles until a close-packed layer is formed (as indicated by no further decrease in IFT upon increasing particle concentration). The consistency of this approach was validated using optical microscopy for microparticles.…”

Section: Introductionmentioning

confidence: 99%

Reversible Adsorption of Nanoparticles at Surfactant-Laden Liquid–Liquid Interfaces

et al. 2019

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In this study, we show that hydrophilic nanoparticles can readily desorb from liquid−liquid interfaces in the presence of surfactants that do not change the wettability of the particles. Our observations are based on a simple theoretical approach to assess the number of adsorbed particles at the surfactant-laden liquid−liquid interface. We test this approach by studying the interfacial self-assembly of equally charged particles and lipids dissolved in separate immiscible phases. Hence, we investigate the interfacial adsorption of aminated silica particles (80 nm) and octadecylamine to the decane/water interface by interfacial tension measurements, which are supplemented by interfacial rheology of the adsorbed interfacial films, scanning electron microscopy images of Langmuir−Blodgett films, and measurements of the three-phase contact angle of the particle surface in the presence of surfactants. The measurements show that particles adsorb at the surfactant-laden interface at all investigated surfactant concentrations and compete with the surfactants for interfacial coverage. Additionally, the wettability of the hydrophilic particles does not change in the presence of the lipids, except for the highest investigated lipid concentration. Comparing the adsorption energies of one particle and of the lipids as a function of the particle contact angle provides an estimate of the tendency for interfacial adsorption of particles from which the particle coverage can be assessed. Based on these findings, equally charged particles and lipids show a competitive behavior at the interface determined by the bulk surfactant concentration and the attachment energies of the particles at the interface. This leads to a simple mechanistic model demonstrating that particles can readily desorb from the interface due to direct displacement by surfactants, which are loosely adsorbed at the oil-facing particle side. This mechanism critically lowers the otherwise high interfacial energy barrier against particle desorption, which otherwise would lead to virtually irreversible particle attachment at the interface.

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Interfacial equation of state for ionized surfactants at oil/water interfaces

Cited by 14 publications

References 31 publications

Revealing the Hidden Details of Nanostructure in a Pharmaceutical Cream

Revealing the Hidden Details of Nanostructure in a Pharmaceutical Cream

The Role of Electrostatic Repulsion on Increasing Surface Activity of Anionic Surfactants in the Presence of Hydrophilic Silica Nanoparticles

Reversible Adsorption of Nanoparticles at Surfactant-Laden Liquid–Liquid Interfaces

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