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Colloids and Interfaces
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Heterogeneous Interfacial Layers – Implications in Thin Liquid Films and...
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Heterogeneous Interfacial Layers – Implications in Thin Liquid Films and Soft Colloids (Dedicated to the 65th Anniversary of Prof. Elena Mileva)

A special issue of Colloids and Interfaces (ISSN 2504-5377).

Deadline for manuscript submissions: closed (30 April 2021) | Viewed by 15129

Special Issue Editor

Dr. Georgi G. Gochev

E-Mail Website
Guest Editor
1. Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30239 Krakow, Poland
2. Institute of Physical Chemistry, Bulgarian Academy of Sciences, Sofia, Bulgaria
Interests: physical chemistry of soft interfaces; adsorption dynamics and surface rheology; structure of interfacial layers; thin liquid films; foams and emulsions; surfactants, polymers and proteins

Special Issue Information

Dear Colleagues,

Soft (liquid/fluid) interfaces play a crucial role in numerous phenomena and processes occurring in nature, technology and other aspects of our everyday life. The scientific understanding of this role began a few centuries ago with the definition of surface tension and has gained momentum with the thermodynamic theory of capillarity by Gibbs. The action of surface forces between two close interfaces—that gives rise to a disjoining pressure in thin liquid films (TLF)—has been well-established as a suitable descriptive formalism of the stability of lyophobic colloids. On this basis, properties and stability of soft colloids are explained by the properties and stability of their interfaces and TLFs as building blocks. During the 20th century, research on surface phenomena in soft colloids was mostly devoted to aqueous solutions of low-molecular-weight surfactants, where the surface layer is assumed as a two-dimensional homogeneous system whose properties do not depend on the position of a selected point in the interface’s plane. Towards the end of that century, interest in macromolecules and supramolecular assemblies as surface-active agents significantly increased, perhaps due to their many types of applications. Heterogeneous interfacial layers are formed on solutions (dispersions) containing macromolecules of synthetic (polymers) or biological (primarily proteins) origins. Furthermore, heterogeneous layers are built up in aqueous mixed systems: protein/surfactant, polymer/surfactant, protein/polymer, solid particle/amphiphile, various coacervates, etc. In the 21st century, there has been a new interest in the surface behavior of supramolecular assemblies like nanogels, soft nanoparticles and fibrillar structures, just to mention a few.

For this Special Issue, we expect contributions related to fundamental and applied research concerning heterogeneous interfacial layers, and we especially encourage works presenting insights into the intrinsic interrelations between interfaces, TLFs and macroscopic colloids. Short communications, original papers and review articles on experimental, theoretical, in silico and other aspects of this topic are welcome.

Dr. Georgi G. Gochev
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Colloids and Interfaces is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Interfacial layers
  • Thin liquid films
  • Foams and emulsions
  • Macromolecules
  • Polymers
  • Proteins
  • Surfactants
  • Solid nanoparticles
  • Soft nanoparticles
  • Microgels
  • Fibrils
  • Coacervates

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Published Papers (5 papers)

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Research

7 pages, 1450 KiB  
Article
Electrohydrodynamic Instabilities in Free Emulsion Films
by Farshid Mostowfi, Plamen Tchoukov, Nikolay Panchev, Tadeusz Dabros and Jan Czarnecki
Colloids Interfaces 2021, 5(3), 36; https://doi.org/10.3390/colloids5030036 - 1 Jul 2021
Viewed by 2974
Abstract
Electrohydrodynamic instabilities were induced in thin water-in-oil emulsion films by application of external DC electric field. The dominant wavelengths of instabilities were measured for constant electric fields of various strengths. The dominant wavelengths agreed reasonably well with theoretical predictions based on a linear [...] Read more.
Electrohydrodynamic instabilities were induced in thin water-in-oil emulsion films by application of external DC electric field. The dominant wavelengths of instabilities were measured for constant electric fields of various strengths. The dominant wavelengths agreed reasonably well with theoretical predictions based on a linear stability model. The linear stability model used in this study took into account experimentally measured repulsive disjoining pressure and calculated Maxwell stress. The observation of such instabilities can help to understand the rupture mechanism of emulsion films under the influence of electric field. Full article
(This article belongs to the Special Issue Heterogeneous Interfacial Layers – Implications in Thin Liquid Films and Soft Colloids (Dedicated to the 65th Anniversary of Prof. Elena Mileva))
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16 pages, 6251 KiB  
Article
Thermodynamics, Kinetics and Dilational Visco-Elasticity of Adsorbed CnEOm Layers at the Aqueous Solution/Air Interface
by Valentin B. Fainerman, Volodymyr I. Kovalchuk, Eugene V. Aksenenko, Francesca Ravera, Libero Liggieri, Giuseppe Loglio, Alexander V. Makievski, Emanuel Schneck and Reinhard Miller
Colloids Interfaces 2021, 5(1), 16; https://doi.org/10.3390/colloids5010016 - 16 Mar 2021
Cited by 3 | Viewed by 2663
Abstract
The adsorption behaviour of linear poly(oxyethylene) alkyl ether (CnEOm) 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 [...] Read more.
The adsorption behaviour of linear poly(oxyethylene) alkyl ether (CnEOm) 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 CnEOm at the water/air interface were determined. For the study, six CnEOm 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. Full article
(This article belongs to the Special Issue Heterogeneous Interfacial Layers – Implications in Thin Liquid Films and Soft Colloids (Dedicated to the 65th Anniversary of Prof. Elena Mileva))
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26 pages, 3696 KiB  
Article
β-Lactoglobulin Adsorption Layers at the Water/Air Surface: 5. Adsorption Isotherm and Equation of State Revisited, Impact of pH
by Georgi G. Gochev, Volodymyr I. Kovalchuk, Eugene V. Aksenenko, Valentin B. Fainerman and Reinhard Miller
Colloids Interfaces 2021, 5(1), 14; https://doi.org/10.3390/colloids5010014 - 5 Mar 2021
Cited by 9 | Viewed by 3072
Abstract
The theoretical description of the adsorption of proteins at liquid/fluid interfaces suffers from the inapplicability of classical formalisms, which soundly calls for the development of more complicated adsorption models. A Frumkin-type thermodynamic 2-d solution model that accounts for nonidealities of interface enthalpy [...] Read more.
The theoretical description of the adsorption of proteins at liquid/fluid interfaces suffers from the inapplicability of classical formalisms, which soundly calls for the development of more complicated adsorption models. A Frumkin-type thermodynamic 2-d solution model that accounts for nonidealities of interface enthalpy and entropy was proposed about two decades ago and has been continuously developed in the course of comparisons with experimental data. In a previous paper we investigated the adsorption of the globular protein β-lactoglobulin at the water/air interface and used such a model to analyze the experimental isotherms of the surface pressure, Π(c), and the frequency-, f-, dependent surface dilational viscoelasticity modulus, E(c)f, in a wide range of protein concentrations, c, and at pH 7. However, the best fit between theory and experiment proposed in that paper appeared incompatible with new data on the surface excess, Γ, obtained from direct measurements with neutron reflectometry. Therefore, in this work, the same model is simultaneously applied to a larger set of experimental dependences, e.g., Π(c), Γ(c), E(Π)f, etc., with E-values measured strictly in the linear viscoelasticity regime. Despite this ambitious complication, a best global fit was elaborated using a single set of parameter values, which well describes all experimental dependencies, thus corroborating the validity of the chosen thermodynamic model. Furthermore, we applied the model in the same manner to experimental results obtained at pH 3 and pH 5 in order to explain the well-pronounced effect of pH on the interfacial behavior of β-lactoglobulin. The results revealed that the propensity of β-lactoglobulin globules to unfold upon adsorption and stretch at the interface decreases in the order pH 3 > pH 7 > pH 5, i.e., with decreasing protein net charge. Finally, we discuss advantages and limitations in the current state of the model. Full article
(This article belongs to the Special Issue Heterogeneous Interfacial Layers – Implications in Thin Liquid Films and Soft Colloids (Dedicated to the 65th Anniversary of Prof. Elena Mileva))
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15 pages, 5286 KiB  
Article
Hydrodynamic Boundary Layers at Solid Wall—A Tool for Separation of Fine Solids
by Ljubomir Nikolov
Colloids Interfaces 2021, 5(1), 11; https://doi.org/10.3390/colloids5010011 - 11 Feb 2021
Viewed by 1786
Abstract
A theoretical study is performed about the hydrodynamic interaction of fine species entrapped in the boundary layer (BL) at solid wall (plate). The key starting point is the analysis of the disturbance introduced by solid spheres in the background fluid flow. For a [...] Read more.
A theoretical study is performed about the hydrodynamic interaction of fine species entrapped in the boundary layer (BL) at solid wall (plate). The key starting point is the analysis of the disturbance introduced by solid spheres in the background fluid flow. For a neutrally buoyant entity, the type of interaction is determined by the size of the spheres as compared to the thickness of the BL region. The result is granulometric separation of the solids inside the BL domain at the wall. The most important result in view of potential applications concerns the so-called small particles Rp < L/ReL5/4 (ReL is the Reynolds number of the background flow and Rp is the radius of the entrapped sphere). In the case of non-neutrally buoyant particles, gravity interferes with the separation effect. Important factor in this case is the relative density of the solid species as compared to this of the fluid. In view of further practical uses, particles within the range of Δρ/ρ < Fr2/ReL1/2 (Fr is Froude number and Δρ/ρ is the relative density of the entrapped solids) are systematically studied. The trajectories inside the BL region of the captured species are calculated. The obtained data show that there are preferred regions along the wall where the fine solids are detained. The results are important for the assessment of the general efficiency of entrapment and segregation of fine species in the vicinity of solid walls and have high potential for further design of industrial separation processes. Full article
(This article belongs to the Special Issue Heterogeneous Interfacial Layers – Implications in Thin Liquid Films and Soft Colloids (Dedicated to the 65th Anniversary of Prof. Elena Mileva))
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20 pages, 7481 KiB  
Article
Preparation of TiO2 Nanoparticle Aggregates and Capsules by the ‘Two-Emulsion Method’
by Nadya I. Politova-Brinkova, Sonya R. Tsibranska-Gyoreva, Slavka S. Tcholakova, Nikolai D. Denkov and Thomas Danner
Colloids Interfaces 2020, 4(4), 57; https://doi.org/10.3390/colloids4040057 - 9 Dec 2020
Cited by 4 | Viewed by 3201
Abstract
TiO2-based materials are of great practical interest in several technological areas. Both the size and the morphology of the TiO2 particles are of critical importance for their applications. The current study explores the effect of several factors on the outcome [...] Read more.
TiO2-based materials are of great practical interest in several technological areas. Both the size and the morphology of the TiO2 particles are of critical importance for their applications. The current study explores the effect of several factors on the outcome of the TiO2 particle synthesis via the so-called ‘two-emulsion method’. In this technique, two water-in-oil emulsions—each of them containing different reactant in the dispersed water drops—are mixed under well controlled conditions. Upon such mixing, partial coalescence of the water drops from the two emulsions leads to mixing of the drop content, with chemical reaction occurring within the drops, and to synthesis of Ti(OH)4 particles. Afterwards, the latter are transformed by emulsion heating into TiO2 particles and aggregates of predominantly anatase structure. Our results show that—depending on the precursor and surfactant concentrations, oil viscosity, emulsification time, and mixing speed—the obtained nanoparticles could aggregate either on the drop surface, forming capsules with a very smooth surface, or inside the water droplets, thus leading to hierarchically structured aggregates of micrometer size. The spherical smooth capsules are constructed of very small monodisperse TiO2 nanoparticles with size below 5 nm. The hierarchical bulk aggregates, on the other hand, are formed from bigger primary particles of sub-micrometer size. The obtained results show that one can obtain various TiO2 structures by controlling the conditions during the emulsion preparation and mixing Full article
(This article belongs to the Special Issue Heterogeneous Interfacial Layers – Implications in Thin Liquid Films and Soft Colloids (Dedicated to the 65th Anniversary of Prof. Elena Mileva))
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