Colloids and Interfaces

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12 pages, 3679 KiB

Open AccessArticle

AFM Slip Length Measurements for Water at Selected Phyllosilicate Surfaces

by Chen Zhang, Xuming Wang, Jiaqi Jin, Lixia Li and Jan D. Miller

Colloids Interfaces 2021, 5(4), 44; https://doi.org/10.3390/colloids5040044 - 1 Oct 2021

Cited by 5 | Viewed by 3909

Abstract

Most reported slip length measurements have been made at the surfaces of synthetic materials and modified synthetic materials. In contrast, few slip length measurements at the surface of unmodified natural mineral surfaces have been reported. In this regard, flow at the silica face [...] Read more.

Most reported slip length measurements have been made at the surfaces of synthetic materials and modified synthetic materials. In contrast, few slip length measurements at the surface of unmodified natural mineral surfaces have been reported. In this regard, flow at the silica face surfaces of the phyllosilicate minerals, talc and mica, was considered. A slip boundary condition was expected at the nonpolar hydrophobic silica surface of talc leading to enhanced flow, and a no-slip boundary condition was expected at the hydrophilic silica surface of mica. Atomic force microscopy (AFM) slip length measurements were made at the talc and mica surfaces. The slip length results for the hydrophobic silica surface of talc were contrasted to the results for the hydrophilic silica surface of mica (no-slip flow). The results are discussed based on molecular dynamics simulations (MDS), as reported in the literature, and AFM images of surface nanobubbles. For nonpolar hydrophobic surfaces (such as talc), it is doubtful that the MDS interfacial water structure and the water exclusion zone (3.2 Å) account for the AFM slip flow with slip lengths as great as 95 nm. Rather, a better explanation for the AFM slip flow condition is based on reduced interfacial viscosity due to the presence of dissolved gas and the accommodation of pancake nanobubbles at the talc surface having a height dimension of magnitude similar to the slip length. Full article

(This article belongs to the Special Issue Interfacial Dynamics)

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21 pages, 7080 KiB

Open AccessArticle

Effect of Surfactant Dynamics on Flow Patterns Inside Drops Moving in Rectangular Microfluidic Channels

by Nina M. Kovalchuk and Mark J. H. Simmons

Colloids Interfaces 2021, 5(3), 40; https://doi.org/10.3390/colloids5030040 - 2 Aug 2021

Cited by 6 | Viewed by 4234

Abstract

Drops contained in an immiscible liquid phase are attractive as microreactors, enabling sound statistical analysis of reactions performed on ensembles of samples in a microfluidic device. Many applications have specific requirements for the values of local shear stress inside the drops and, thus, [...] Read more.

Drops contained in an immiscible liquid phase are attractive as microreactors, enabling sound statistical analysis of reactions performed on ensembles of samples in a microfluidic device. Many applications have specific requirements for the values of local shear stress inside the drops and, thus, knowledge of the flow field is required. This is complicated in commonly used rectangular channels by the flow of the continuous phase in the corners, which also affects the flow inside the drops. In addition, a number of chemical species are present inside the drops, of which some may be surface-active. This work presents a novel experimental study of the flow fields of drops moving in a rectangular microfluidic channel when a surfactant is added to the dispersed phase. Four surfactants with different surface activities are used. Flow fields are measured using Ghost Particle Velocimetry, carried out at different channel depths to account for the 3-D flow structure. It is shown that the effect of the surfactant depends on the characteristic adsorption time. For fast-equilibrating surfactants with a characteristic time scale of adsorption that is much smaller than the characteristic time of surface deformation, this effect is related only to the decrease in interfacial tension, and can be accounted for by the change in capillary number. For slowly equilibrating surfactants, Marangoni stresses accelerate the corner flow, which changes the flow patterns inside the drop considerably. Full article

(This article belongs to the Special Issue Interfacial Dynamics)

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15 pages, 2574 KiB

Open AccessArticle

A Multistate Adsorption Model for the Adsorption of C₁₄EO₄ and C₁₄EO₈ at the Solution/Air Interface

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

Colloids Interfaces 2021, 5(3), 39; https://doi.org/10.3390/colloids5030039 - 29 Jul 2021

Cited by 11 | Viewed by 2698

Abstract

The dynamic and equilibrium properties of adsorption layers of poly (oxyethylene) alkyl ether (C_nEO_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 [...] Read more.

The dynamic and equilibrium properties of adsorption layers of poly (oxyethylene) alkyl ether (C_nEO_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 C₁₄EO₄ and C₁₄EO₈ (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_nEO_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 C₁₄EO₄, the assumption of s = 5 adsorption states provides a much better agreement than for s = 2, while for C₁₄EO₈, a number of s = 10 adsorption states allows an optimum data description. Full article

(This article belongs to the Special Issue Interfacial Dynamics)

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17 pages, 2307 KiB

Open AccessArticle

Ion-Specific and Solvent Effects on PDADMA–PSS Complexation and Multilayer Formation

by Jasmina Jukić, Karla Korade, Ana-Marija Milisav, Ida Delač Marion and Davor Kovačević

Colloids Interfaces 2021, 5(3), 38; https://doi.org/10.3390/colloids5030038 - 21 Jul 2021

Cited by 9 | Viewed by 3989

Abstract

Among various parameters that influence the formation of polyelectrolyte complexes and multilayers, special emphasis should be placed on ion-specific and solvent effects. In our study, we systematically examined the above-mentioned effects on poly(diallyldimethylammonium chloride) (PDADMACl)-sodium poly(4-styrenesulfonate) (NaPSS) complexation in solution and at the [...] Read more.

Among various parameters that influence the formation of polyelectrolyte complexes and multilayers, special emphasis should be placed on ion-specific and solvent effects. In our study, we systematically examined the above-mentioned effects on poly(diallyldimethylammonium chloride) (PDADMACl)-sodium poly(4-styrenesulfonate) (NaPSS) complexation in solution and at the surface by means of dynamic light scattering, ellipsometry and atomic force microscopy measurements. As solvents, we used water and water/ethanol mixture. The obtained results confirm the importance of ion-specific and solvent effects on complexes prepared in solution, as well as on multilayers built up on a silica surface. The experiments in mixed solvent solution showed that at a higher ethanol mole fraction, the decrease in monomer titrant to titrand ratio, at which the increase in the size of complexes is observed, takes place. The difference between chloride and bromide ions was more pronounced at a higher mole fraction of ethanol and in the case of positive complex formation, suggesting that the larger amount of bromide ions could be condensed to the polycation chain. These findings are in accordance with the results we obtained for polyelectrolyte multilayers and could be helpful for designing polyelectrolyte multilayers with tuned properties needed for various applications, primarily in the field of biomedicine. Full article

(This article belongs to the Special Issue Interfacial Dynamics)

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11 pages, 28258 KiB

Open AccessArticle

Understanding the Dynamics of a Lipid Monolayer on a Water Surface under a Marangoni Flow

by Yohko F. Yano, Toshiaki Ina and Tomoya Uruga

Colloids Interfaces 2021, 5(2), 31; https://doi.org/10.3390/colloids5020031 - 2 Jun 2021

Cited by 2 | Viewed by 2966

Abstract

Biological membrane is composed of lipid molecules, because of its fluidity, it is possible to carry out physiological functions. Therefore, it is important to study the hydrodynamic properties of membranes toward understanding its function. Here, we observed the dynamical behavior of a lipid [...] Read more.

Biological membrane is composed of lipid molecules, because of its fluidity, it is possible to carry out physiological functions. Therefore, it is important to study the hydrodynamic properties of membranes toward understanding its function. Here, we observed the dynamical behavior of a lipid monolayer on the water surface under Marangoni flow. By using X-ray reflectometry, we obtained the tilt angle of the hydrocarbon chains of the lipid at different surface pressures. Comparing them with the dynamical surface pressure under Marangoni flow, it was found that the lipid molecules in rotational rather than translational motion. At low surface pressure, the molecular tilt angle is reduced by 20 degrees, even though the molecular area is reduced by at most 10%. Full article

(This article belongs to the Special Issue Interfacial Dynamics)

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19 pages, 5037 KiB

Open AccessArticle

Monolayers of Cholesterol and Cholesteryl Stearate at the Water/Vapor Interface: A Physico-Chemical Study of Components of the Meibum Layer

by Ramón G. Rubio, Eduardo Guzmán, Francisco Ortega and Libero Liggieri

Colloids Interfaces 2021, 5(2), 30; https://doi.org/10.3390/colloids5020030 - 20 May 2021

Cited by 8 | Viewed by 2885

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Interfacial Dynamics)

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Review

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22 pages, 2853 KiB

Open AccessReview

The Oscillatory Spinning Drop Technique. An Innovative Method to Measure Dilational Interfacial Rheological Properties of Brine-Crude Oil Systems in the Presence of Asphaltenes

by Ronald Marquez, Johnny Bullon, Ana Forgiarini and Jean-Louis Salager

Colloids Interfaces 2021, 5(3), 42; https://doi.org/10.3390/colloids5030042 - 4 Aug 2021

Cited by 11 | Viewed by 5457

Abstract

The oscillatory spinning drop method has been proven recently to be an accurate technique to measure dilational interfacial rheological properties. It is the only available equipment for measuring dilational moduli in low interfacial tension systems, as it is the case in applications dealing [...] Read more.

The oscillatory spinning drop method has been proven recently to be an accurate technique to measure dilational interfacial rheological properties. It is the only available equipment for measuring dilational moduli in low interfacial tension systems, as it is the case in applications dealing with surfactant-oil-water three-phase behavior like enhanced oil recovery, crude oil dehydration, or extreme microemulsion solubilization. Different systems can be studied, bubble-in-liquid, oil-in-water, microemulsion-in-water, oil-in-microemulsion, and systems with the presence of complex natural surfactants like asphaltene aggregates or particles. The technique allows studying the characteristics and properties of water/oil interfaces, particularly when the oil contains asphaltenes and when surfactants are present. In this work, we present a review of the measurements of crude oil-brine interfaces with the oscillating spinning drop technique. The review is divided into four sections. First, an introduction on the oscillating spinning drop technique, fundamental and applied concepts are presented. The three sections that follow are divided according to the complexity of the systems measured with the oscillating spinning drop, starting with simple surfactant-oil-water systems. Then the complexity increases, presenting interfacial rheology properties of crude oil-brine systems, and finally, more complex surfactant-crude oil-brine systems are reviewed. We have found that using the oscillating spinning drop method to measure interfacial rheology properties can help make precise measurements in a reasonable amount of time. This is of significance when systems with long equilibration times, e.g., asphaltene or high molecular weight surfactant-containing systems are measured, or with systems formulated with a demulsifier which is generally associated with low interfacial tension. Full article

(This article belongs to the Special Issue Interfacial Dynamics)

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27 pages, 2922 KiB

Open AccessReview

Water and Ion Dynamics in Confined Media: A Multi-Scale Study of the Clay/Water Interface

by Patrice Porion, Ali Asaad, Thomas Dabat, Baptiste Dazas, Alfred Delville, Eric Ferrage, Fabien Hubert, Mónica Jiménez-Ruiz, Laurent J. Michot, Sébastien Savoye and Emmanuel Tertre

Colloids Interfaces 2021, 5(2), 34; https://doi.org/10.3390/colloids5020034 - 15 Jun 2021

Cited by 5 | Viewed by 3808

Abstract

This review details a large panel of experimental studies (Inelastic Neutron Scattering, Quasi-Elastic Neutron Scattering, Nuclear Magnetic Resonance relaxometry, Pulsed-Gradient Spin-Echo attenuation, Nuclear Magnetic Resonance Imaging, macroscopic diffusion experiments) used recently to probe, over a large distribution of characteristic times (from pico-second up [...] Read more.

This review details a large panel of experimental studies (Inelastic Neutron Scattering, Quasi-Elastic Neutron Scattering, Nuclear Magnetic Resonance relaxometry, Pulsed-Gradient Spin-Echo attenuation, Nuclear Magnetic Resonance Imaging, macroscopic diffusion experiments) used recently to probe, over a large distribution of characteristic times (from pico-second up to days), the dynamical properties of water molecules and neutralizing cations diffusing within clay/water interfacial media. The purpose of this review is not to describe these various experimental methods in detail but, rather, to investigate the specific dynamical information obtained by each of them concerning these clay/water interfacial media. In addition, this review also illustrates the various numerical methods (quantum Density Functional Theory, classical Molecular Dynamics, Brownian Dynamics, macroscopic differential equations) used to interpret these various experimental data by analyzing the corresponding multi-scale dynamical processes. The purpose of this multi-scale study is to perform a bottom-up analysis of the dynamical properties of confined ions and water molecules, by using complementary experimental and numerical studies covering a broad range of diffusion times (between pico-seconds up to days) and corresponding diffusion lengths (between Angstroms and centimeters). In the context of such a bottom-up approach, the numerical modeling of the dynamical properties of the diffusing probes is based on experimental or numerical investigations performed on a smaller scale, thus avoiding the use of empirical or fitted parameters. Full article

(This article belongs to the Special Issue Interfacial Dynamics)

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