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Article ; Online: Monolayers of Cholesterol and Cholesteryl Stearate at the Water/Vapor Interface

Ramón G. Rubio / Eduardo Guzmán / Francisco Ortega / Libero Liggieri

Colloids and Interfaces, Vol 5, Iss 30, p

A Physico-Chemical Study of Components of the Meibum Layer

2021 Volume 30

Abstract: Langmuir monolayers containing different amounts of cholesterol and cholesteryl stearate were studied at two different temperatures (24 °C and 35 °C). The main goal was to contribute towards the understanding of how the variations in the chemical ... ...

Abstract	Langmuir monolayers containing different amounts of cholesterol and cholesteryl stearate were studied at two different temperatures (24 °C and 35 °C). The main goal was to contribute towards the understanding of how the variations in the chemical composition may affect the physico-chemical properties of these specific lipid monolayers. The model mixture was chosen considering that cholesteryl esters are present in cell membranes and some other biological systems, including human tear lipids. Therefore, an investigation into the effect of the lipid monolayer composition on their interfacial properties may elucidate some of the fundamental reasons for the deficiencies in cell membranes and tear film functioning in vivo. The experimental results have shown that the molar ratio of the mixture plays a crucial role in the modulation of the Langmuir film properties. The condensing effects of the cholesterol and the interactions between the lipids in the monolayer were the main factors altering the monolayer response to dilatational deformation. The modification of the mixture compositions leads to significant changes in the Langmuir films and the mechanical performance, altering the ability of the monolayer to reduce the surface tension and the viscoelastic properties of the monolayers. This suggests that subtle modifications of the biomembrane composition may significantly alter its physiological function.
Keywords	Langmuir monolayers ; dilational rheology ; cholesterol ; cholesteryl stearate ; Chemistry ; QD1-999
Subject code	540
Language	English
Publishing date	2021-05-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Surface Properties of Saponin—Chitosan Mixtures

Marcel Krzan / Natalia García Rey / Ewelina Jarek / Agnieszka Czakaj / Eva Santini / Francesca Ravera / Libero Liggieri / Piotr Warszynski / Björn Braunschweig

Molecules, Vol 27, Iss 7505, p

2022 Volume 7505

Abstract: The surface properties of saponin and saponin-chitosan mixtures were analysed as a function of their bulk mixing ratio using vibrational sum-frequency generation (SFG), surface tensiometry and dilational rheology measurements. Our experiments show that ... ...

Abstract	The surface properties of saponin and saponin-chitosan mixtures were analysed as a function of their bulk mixing ratio using vibrational sum-frequency generation (SFG), surface tensiometry and dilational rheology measurements. Our experiments show that saponin-chitosan mixtures present some remarkable properties, such as a strong amphiphilicity of the saponin and high dilational viscoelasticity. We believe this points to the presence of chitosan in the adsorption layer, despite its complete lack of surface activity. We explain this phenomenon by electrostatic interactions between the saponin as an anionic surfactant and chitosan as a polycation, leading to surface-active saponin-chitosan complexes and aggregates. Analysing the SFG intensity of the O-H stretching bands from interfacial water molecules, we found that in the case of pH 3.4 for a mixture consisting of 0.1 g/L saponin and 0.001 g/L chitosan, the adsorption layer was electrically neutral. This conclusion from SFG spectra is corroborated by results from surface tensiometry showing a significant reduction in surface tension and effects on the dilational surface elasticity strictly at saponin/chitosan ratios, where SFG spectra indicate zero net charge at the air–water interface.
Keywords	saponin ; chitosan ; saponin—chitosan interactions ; bio-compatible systems ; biodegradable surfactants ; Organic chemistry ; QD241-441
Subject code	540
Language	English
Publishing date	2022-11-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Effects of Oil Phase on the Inversion of Pickering Emulsions Stabilized by Palmitic Acid Decorated Silica Nanoparticles

Andrés González-González / Natalia Sánchez-Arribas / Eva Santini / José Luis Rodríguez-Villafuerte / Carlo Carbone / Francesca Ravera / Francisco Ortega / Libero Liggieri / Ramón G. Rubio / Eduardo Guzmán

Colloids and Interfaces, Vol 6, Iss 27, p

2022 Volume 27

Abstract: Pickering emulsions stabilized by the interaction of palmitic acid (PA) and silica nanoparticles (SiNPs) at the water/oil interface have been studied using different alkane oil phases. The interaction of palmitic acid and SiNPs has a strong synergistic ... ...

Abstract	Pickering emulsions stabilized by the interaction of palmitic acid (PA) and silica nanoparticles (SiNPs) at the water/oil interface have been studied using different alkane oil phases. The interaction of palmitic acid and SiNPs has a strong synergistic character in relation to the emulsion stabilization, leading to an enhanced emulsion stability in relation to that stabilized only by the fatty acid. This results from the formation of fatty acid-nanoparticle complexes driven by hydrogen bond interactions, which favor particle attachment at the fluid interface, creating a rigid armor that minimizes droplet coalescence. The comparison of emulsions obtained using different alkanes as the oil phase has shown that the hydrophobic mismatch between the length of the alkane chain and the C16 hydrophobic chain of PA determines the nature of the emulsions, with the solubility of the fatty acid in the oil phase being a very important driving force governing the appearance of phase inversion.
Keywords	emulsions ; fatty acid ; hydrophobic mismatch ; phase inversion ; Pickering ; silica nanoparticles ; Chemistry ; QD1-999
Subject code	540
Language	English
Publishing date	2022-04-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Interfacial Properties of Tridecyl Dimethyl Phosphine Oxide Adsorbed at the Surface of a Solution Drop in Hexane Saturated Air

Valentin B. Fainerman / Eugene V. Aksenenko / Alexander V. Makievski / Libero Liggieri / Nenad Mucic / Aliyar Javadi / Volodymyr I. Kovalchuk / Reinhard Miller

Colloids and Interfaces, Vol 4, Iss 19, p

2020 Volume 19

Abstract: The surface tension of C 13 DMPO aqueous solution drops in hexane vapor is studied using the drop profile method. The hexane was injected into the measuring cell at three different conditions: before the formation of the solution drop, at a certain ... ...

Abstract	The surface tension of C 13 DMPO aqueous solution drops in hexane vapor is studied using the drop profile method. The hexane was injected into the measuring cell at three different conditions: before the formation of the solution drop, at a certain moment during the adsorption process, and after reaching the equilibrium of surfactant adsorption. The surface tension values for all experiments at the same concentration and different injection situations ultimately coincide with each other after attaining the final equilibration stage. The equilibrium surface tension isotherms of C 13 DMPO solutions, and the adsorption of both components—surfactant and hexane—were calculated. It was shown that the presence of surfactant leads to an increased hexane adsorption.
Keywords	drop profile analysis tensiometry ; surfactant adsorption ; solution–alkane vapor interface ; dynamic surface tension ; thermodynamic model ; non-ionic surfactant ; Chemistry ; QD1-999
Subject code	620
Language	English
Publishing date	2020-04-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: The Role of Endogenous Proteins on the Emulsification of Silicone Oils Used in Vitreoretinal Surgery

Irene Nepita / Rodolfo Repetto / Jan O. Pralits / Mario R. Romano / Francesca Ravera / Eva Santini / Libero Liggieri

BioMed Research International, Vol

2020 Volume 2020

Abstract: The present work is aimed at investigating the chemicophysical properties of the interface between silicone oils (SOs) used in vitreoretinal surgery and aqueous solutions, in the presence of surfactant biomolecules. Such molecules are thought to play an ... ...

Abstract	The present work is aimed at investigating the chemicophysical properties of the interface between silicone oils (SOs) used in vitreoretinal surgery and aqueous solutions, in the presence of surfactant biomolecules. Such molecules are thought to play an important role in the formation of SO emulsions in vitrectomised eyes, in which the natural vitreous body has been replaced with a SO. In particular, we have measured the interfacial tension (IT) and the interfacial dilational viscoelasticity (DV) of the interface between SO (Siluron 1000) and serum proteins (albumin and γ-globulins) at various concentrations in a Dulbecco alkaline buffer. The equilibrium IT value is relevant for the onset of emulsification, and the DV influences the stability of an emulsion, once formed. The study is complemented by preliminary emulsification tests. The experimental results show that, when proteins are dissolved in the aqueous solution, the rheological properties of the interface change. The IT decreases significantly for physiological protein concentrations, and the DV modulus achieves high values, even for small protein concentrations. The emulsification tests confirm that, in the presence of proteins, emulsions are stable on the time scale of months. We conclude that the measured values of IT in the presence of serum proteins are compatible with the promotion of droplet formation, which, in addition, are expected to be stable against coalescence. Adsorption of biomolecules at the interface with the SO is, therefore, likely to play an important role in the generation of an emulsion in eyes subjected to vitrectomy. These findings are relevant to identify strategies to avoid or control the formation of emulsions in eyes.
Keywords	Medicine ; R
Subject code	612
Language	English
Publishing date	2020-01-01T00:00:00Z
Publisher	Hindawi Limited
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article: Adsorption of Sodium Dodecyl Sulfate at Water–Dodecane Interface in Relation to the Oil in Water Emulsion Properties

Llamas, Sara / Davide Orsi / Eva Santini / Fabrizia Salerni / Francesca Ravera / Libero Liggieri / Luigi Cristofolini

Langmuir. 2018 May 02, v. 34, no. 21

2018

Abstract: The control of the behavior of oil in water emulsions requires deeper investigations on the adsorption properties of the emulsion stabilizers at the interfaces, which are fundamental to explain the (de)stabilization mechanisms. In this work, we present ... ...

Abstract	The control of the behavior of oil in water emulsions requires deeper investigations on the adsorption properties of the emulsion stabilizers at the interfaces, which are fundamental to explain the (de)stabilization mechanisms. In this work, we present an extensive study on oil-in-water emulsions stabilized by sodium dodecyl sulfate (SDS) below its critical micellar concentration. Dynamic tensiometry, dilational rheology, and electrical conductivity measurements are used to investigate the adsorption properties at the droplet interface, whereas the aging of the respective emulsions was investigated by monitoring the macroscopic thickness of the emulsion layer, by microimaging and dynamic light scattering (DLS) analysis, to get information on the drop size distribution. In addition, the droplet coalescence is investigated by a microscopy setup. The results of this multitechnique study allow deriving a coherent scenario where the adsorption properties of this ionic surfactant relate to those of the emulsion, such as, for example, the prevention of droplet coalescence and the presence of other mechanisms, such as Ostwald ripening, responsible for the emulsion aging.
Keywords	adsorption ; droplets ; electrical conductivity ; emulsifying properties ; emulsions ; ionic surfactants ; light scattering ; microscopy ; monitoring ; oils ; Ostwald ripening ; rheology ; sodium dodecyl sulfate ; stabilizers
Language	English
Dates of publication	2018-0502
Size	p. 5978-5989.
Publishing place	American Chemical Society
Document type	Article
ZDB-ID	2005937-1
ISSN	1520-5827 ; 0743-7463
ISSN (online)	1520-5827
ISSN	0743-7463
DOI	10.1021/acs.langmuir.8b00358
Database	NAL-Catalogue (AGRICOLA)

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Article ; Online: A Multistate Adsorption Model for the Adsorption of C 14 EO 4 and C 14 EO 8 at the Solution/Air Interface

Valentin B. Fainerman / Volodymyr I. Kovalchuk / Eugene V. Aksenenko / Francesca Ravera / Libero Liggieri / Giuseppe Loglio / Alexander V. Makievski / Natalia O. Mishchuk / Emanuel Schneck / Reinhard Miller

Colloids and Interfaces, Vol 5, Iss 39, p

2021 Volume 39

Abstract: The dynamic and equilibrium properties of adsorption layers of poly (oxyethylene) alkyl ether (C n EO m ) can be well described by the reorientation model. In its classical version, it assumes two adsorption states; however, there are obviously ... ...

Abstract	The dynamic and equilibrium properties of adsorption layers of poly (oxyethylene) alkyl ether (C n EO m ) can be well described by the reorientation model. In its classical version, it assumes two adsorption states; however, there are obviously surfactants that can adsorb in more than two possible conformations. The experimental data for C 14 EO 4 and C 14 EO 8 (dynamic and equilibrium surface tensions and surface dilational visco-elasticity as measured by bubble profile analysis tensiometry) are used to verify if a reorientation model with more than two possible adsorption states can better describe the complete set data of C n EO m adsorption layers at the water/air interface. The proposed refined theoretical model allows s different states of the adsorbing molecules at the interface. The comparison between the model and experiment demonstrates that, for C 14 EO 4 , the assumption of s = 5 adsorption states provides a much better agreement than for s = 2, while for C 14 EO 8 , a number of s = 10 adsorption states allows an optimum data description.
Keywords	poly (oxyethylene) alkyl ether ; dynamic surface tension ; surface tension isotherm ; dilational surface visco-elasticity ; diffusion controlled adsorption ; reorientation adsorption model ; Chemistry ; QD1-999
Subject code	290
Language	English
Publishing date	2021-07-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Thermodynamics, Kinetics and Dilational Visco‑Elasticity of Adsorbed C n EO m Layers at the Aqueous Solution/Air Interface

Valentin B. Fainerman / Volodymyr I. Kovalchuk / Eugene V. Aksenenko / Francesca Ravera / Libero Liggieri / Giuseppe Loglio / Alexander V. Makievski / Emanuel Schneck / Reinhard Miller

Colloids and Interfaces, Vol 5, Iss 16, p

2021 Volume 16

Abstract: The adsorption behaviour of linear poly(oxyethylene) alkyl ether (C n EO m ) is best described by a reorientation model. Based on a complete set of experimental data, including the adsorption kinetics, the equilibrium surface tension isotherm and the ... ...

Abstract	The adsorption behaviour of linear poly(oxyethylene) alkyl ether (C n EO m ) is best described by a reorientation model. Based on a complete set of experimental data, including the adsorption kinetics, the equilibrium surface tension isotherm and the surface dilational visco-elasticity, the thermodynamic and kinetic adsorption parameters for some C n EO m at the water/air interface were determined. For the study, six C n EO m surfactants were selected ( n = 10, 12 and 14 and m = 4, 5 and 8) and were studied by bubble profile analysis and maximum bubble pressure tensiometry. A refined theoretical model based on a reorientation-adsorption model combined with a diffusion-controlled adsorption kinetics and exchange of matter allowed us to calculate the surface layer composition by adsorbing molecules in different orientations. It turns out that at larger surface coverage, the adsorption rate decreases, i.e., the apparent diffusion coefficients are smaller. This deceleration can be explained by the transition of molecules adsorbed in a state of larger molar surface area into a state with smaller molar surface area.
Keywords	poly(oxyethylene) alkyl ether ; adsorption kinetics ; surface tension isotherm ; dilational surface visco-elasticity ; diffusion-controlled adsorption ; reorientation model ; Chemistry ; QD1-999
Subject code	541
Language	English
Publishing date	2021-03-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Effect of Temperature on the Dynamic Properties of Mixed Surfactant Adsorbed Layers at the Water/Hexane Interface under Low-Gravity Conditions

Volodymyr I. Kovalchuk / Giuseppe Loglio / Alexey G. Bykov / Michele Ferrari / Jürgen Krägel / Libero Liggieri / Reinhard Miller / Olga Yu. Milyaeva / Boris A. Noskov / Francesca Ravera / Eva Santini / Emanuel Schneck

Colloids and Interfaces, Vol 4, Iss 27, p

2020 Volume 27

Abstract: An increase in temperature typically leads to a decrease in the interfacial tension of a water/oil interface. The addition of surfactants to the system can complicate the situation significantly, i.e., the interfacial tension can increase or decrease ... ...

Abstract	An increase in temperature typically leads to a decrease in the interfacial tension of a water/oil interface. The addition of surfactants to the system can complicate the situation significantly, i.e., the interfacial tension can increase or decrease with an increasing temperature. For most concentrations of the two studied surfactants, the cationic tetradecyl trimethyl ammonium bromide (TTAB) and the nonionic tridecyl dimethyl phosphine oxide (C 13 DMPO), the measured interfacial tension of the aqueous mixed surfactant solutions against hexane increases when the temperature decreases between 30 °C and 20 °C. However, with a further temperature decrease between 20 °C and 15 °C, the reverse effect has also been observed at some concentrations, i.e., a decrease of interfacial tension. Additionally, the corresponding dilational interfacial visco-elasticity shows some discrepant temperature effects, depending on the bulk concentration and oscillation frequency. The experiments have been performed with a capillary pressure tensiometer under the conditions of micro-gravity. The reason for the positive and negative interfacial tension and visco-elasticity gradients, respectively, within certain ranges of the temperature, concentration and mixing ratios, are discussed on the basis of all available parameters, such as the solubility and partitioning of the surfactants in the two liquid phases and the oscillation frequency.
Keywords	interfacial dilational viscoelasticity ; mixed surfactant adsorption layer ; water/hexane interface ; drop oscillations ; capillary pressure tensiometry ; effect of temperature ; Chemistry ; QD1-999
Subject code	541
Language	English
Publishing date	2020-07-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Drop Size Dependence of the Apparent Surface Tension of Aqueous Solutions in Hexane Vapor as Studied by Drop Profile Analysis Tensiometry

Valentin B. Fainerman / Volodymyr I. Kovalchuk / Eugene V. Aksenenko / Altynay A. Sharipova / Libero Liggieri / Aliyar Javadi / Alexander V. Makievski / Mykola V. Nikolenko / Saule B. Aidarova / Reinhard Miller

Colloids and Interfaces, Vol 4, Iss 29, p

2020 Volume 29

Abstract: Surface tension experiments were performed using the drop profile analysis tensiometry method. The hexane was injected into the measuring cell at certain times before the formation of the solution drop. The influence of the capillary diameter and ... ...

Abstract	Surface tension experiments were performed using the drop profile analysis tensiometry method. The hexane was injected into the measuring cell at certain times before the formation of the solution drop. The influence of the capillary diameter and solution drop size on the measured apparent dynamic surface tension was studied. The amount of hexane transferred from the vapor phase to the drop was estimated. For large pure water drops, it was shown that the ageing of the drop in the hexane vapor during a long time resulted in the formation of a liquid hexane phase covering the drop, but the volume of this phase did not exceed 0.5 mm 3 . On the contrary, for surfactant solution drops the volume of the hexane phase covering the drop was essentially larger. Experiments with solution drops were performed to measure the surface tension within a wide range of surfactant concentration. It was found that the dependencies of dynamic surface tension on the C 13 DMPO and C 14 EO 8 solutions concentration exhibit maxima at concentrations of about 1–2 μmol/L for C 14 EO 8 and 2–5 μmol/L for C 13 DMPO at ageing times of 100 to 1000 s; these maxima were shown to exist also at equilibrium. This phenomenon is presumably ascribed to the competitive character of simultaneous adsorption of hexane and surfactant.
Keywords	drop profile analysis tensiometry ; solution–alkane vapor interface ; dynamic apparent surface tension ; non-ionic surfactant ; thermodynamic model ; Chemistry ; QD1-999
Subject code	620
Language	English
Publishing date	2020-07-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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