Special Issue "B&D 2019"

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

Deadline for manuscript submissions: closed (29 February 2020).

Special Issue Editors

Dr. Reinhard Miller
Website
Guest Editor
Max Planck Institute of Colloids and Interfaces, D-14424, Potsdam, Germany
Interests: dynamics and mechanics of liquid interfaces; thermodynamics of adsorption of surfactants and proteins; interfacial interactions and 2D rheology; stability of foams and emulsions
Special Issues and Collections in MDPI journals
Prof. Dr. Elena Mileva

Guest Editor
Head of Department of Interfaces and Colloids, Institute of Physical Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl.11, 1113 Sofia, Bulgaria
Interests: soft matter physics, complex fluids; surface forces and thin liquid films; bulk and interfacial rheology; amphiphilic self-assembly; biomedical and ecological aspects and applications of supramolecular structures in fluid media

Special Issue Information

Dear Colleagues,

The 8th Bubble and Drop Conference (https://bd2019.eu/) will take place in Sofia, Bulgaria, 24–28 June 2019. This interdisciplinary forum will gather scientists from academia and industry, working on the front-line topics focused on bubbles, drops, interfaces, foams, and emulsions. The B&D 2019 Conference will provide a wide opportunity for the exchange of new ideas in the areas of: adsorption and wetting phenomena; surface forces, superhydrophobicity, patches, and layering; nano/microscale stability and sustainability; engineered interfaces and smart nanostructured materials; and formulations and innovations for industrial applications.

Participants of the B&D 2019 Conference are cordially invited to contribute original research papers to this Special Issue of Colloids and Interfaces.

Dr. Reinhard Miller
Prof. Elena Mileva
Guest Editors

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 papers will be 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 quarterly 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 1000 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

  • adsorption and wetting phenomena
  • surface forces, superhydrophobicity, patches, and layering
  • nano/microscale stability and sustainability
  • engineered interfaces and smart nanostructured materials
  • formulations and innovations for industrial applications

Published Papers (6 papers)

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Research

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Open AccessArticle
Investigation of Single and Binary of “Sandwich” Type Convex Liquid Capillary Bridges, Stretched between Two Flat Surfaces (Experimental Approach)
Colloids Interfaces 2019, 3(4), 68; https://doi.org/10.3390/colloids3040068 - 12 Dec 2019
Abstract
The interest to monophasic liquid capillary bridges (CB) has a long history. These shapes are attractive not only because of their interesting surface properties but also because of the possibility of their behavior to be analytically predicted by the equations of differential geometry. [...] Read more.
The interest to monophasic liquid capillary bridges (CB) has a long history. These shapes are attractive not only because of their interesting surface properties but also because of the possibility of their behavior to be analytically predicted by the equations of differential geometry. In the current paper we extend our previous studies by implementation of an approach for prediction of liquid gravityless CB behavior during their quasi-static stretching. It was found, that a simple linear relation, h r m ~ ln R r m , is valid the case of good wetting, 0° ≤ θ ≤ 90°, where h is the height of CB, R is the radius at the contact surface, rm is the CB waist radius, and θ is the solid/liquid (static, receding) contact angle. We experimentally studied the geometrical properties evolution of monophasic cedar oil and water CBs between two glass plates during their quasi-static (stepwise with equilibration after each step for 1–2 min.) stretching. In addition, we investigated a binary CB of a new type, resembling “sandwich”. There, due to the stronger glass wetting by the water, the oil phase is adhered at the water/gas interface, partially engulfed with a tendency to stand in the zone around the waist (minimal surface energy). During the stretching, it tends to replace the water in the CB waist region. A simple mechanism for interaction of the two immiscible liquids leading to creation of “sandwich” like binary structures, is proposed. Experiments of capillary bridges (CB) stretching between two flat surfaces have been carried for all liquids at different volume proportions. The investigation is extended also to identification of CB profile generatrix shape. We experimentally found that for monophasic CB, it can be described by a circle during the quasi-static stretching. If the CB height is increased, before the rupture, the shape evolves consecutively to an ellipse, parabola, or possibly to a hyperbola. The investigated binary CB evolves a similar way. Conclusions are drawn and directions for further investigations are given. Full article
(This article belongs to the Special Issue B&D 2019)
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Open AccessFeature PaperArticle
Cooperative Effects in Surfactant Adsorption Layers at Water/Alkane Interfaces
Colloids Interfaces 2019, 3(4), 67; https://doi.org/10.3390/colloids3040067 - 12 Dec 2019
Cited by 1
Abstract
In the present work, the properties of dodecyl dimethyl phosphine oxide (C12DMPO) at the water/decane interface are studied and compared with those obtained earlier at the interface to hexane. To simulate the interfacial behavior, a two-component thermodynamic model is proposed, which [...] Read more.
In the present work, the properties of dodecyl dimethyl phosphine oxide (C12DMPO) at the water/decane interface are studied and compared with those obtained earlier at the interface to hexane. To simulate the interfacial behavior, a two-component thermodynamic model is proposed, which combines the equation of state and Frumkin isotherm for decane with the reorientation model involving the intrinsic compressibility for the surfactant. In this approach, the surface activity of decane is governed by its interaction with C12DMPO. The theory predicts the influence of decane on the decrease of the surface tension at a very low surfactant concentration for realistic values of the ratio of the adsorbed amounts of decane and surfactant. The surfactant’s distribution coefficient between the aqueous and decane phases is determined. Two types of adsorption systems were used: a decane drop immersed into the C12DMPO aqueous solution, and a water drop immersed into the C12DMPO solution in decane. To determine the distribution coefficient, a method based on the analysis of the transfer of C12DMPO between water and decane is also employed. Full article
(This article belongs to the Special Issue B&D 2019)
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Open AccessFeature PaperCommunication
Interfacial Dilational Viscoelasticity of Adsorption Layers at the Hydrocarbon/Water Interface: The Fractional Maxwell Model
Colloids Interfaces 2019, 3(4), 66; https://doi.org/10.3390/colloids3040066 - 10 Dec 2019
Abstract
In this communication, the single element version of the fractional Maxwell model (single-FMM or Scott–Blair model) is adopted to quantify the observed behavior of the linear interfacial dilational viscoelasticity. This mathematical tool is applied to the results obtained by capillary pressure experiments under [...] Read more.
In this communication, the single element version of the fractional Maxwell model (single-FMM or Scott–Blair model) is adopted to quantify the observed behavior of the linear interfacial dilational viscoelasticity. This mathematical tool is applied to the results obtained by capillary pressure experiments under low-gravity conditions aboard the International Space Station, for adsorption layers at the hydrocarbon/water interface. Two specific experimental sets of steady-state harmonic oscillations of interfacial area are reported, respectively: a drop of pure water into a Span-80 surfactant/paraffin-oil matrix and a pure n-hexane drop into a C13DMPO/TTAB mixed surfactants/aqueous-solution matrix. The fractional constitutive single-FMM is demonstrated to embrace the standard Maxwell model (MM) and the Lucassen–van-den-Tempel model (L–vdT), as particular cases. The single-FMM adequately fits the Span-80/paraffin-oil observed results, correctly predicting the frequency dependence of the complex viscoelastic modulus and the inherent phase-shift angle. In contrast, the single-FMM appears as a scarcely adequate tool to fit the observed behavior of the mixed-adsorption surfactants for the C13DMPO/TTAB/aqueous solution matrix (despite the single-FMM satisfactorily comparing to the phenomenology of the sole complex viscoelastic modulus). Further speculations are envisaged in order to devise combined FMM as rational guidance to interpret the properties and the interfacial structure of complex mixed surfactant adsorption systems. Full article
(This article belongs to the Special Issue B&D 2019)
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Open AccessArticle
Comparison of Bubble Size Distributions Inferred from Acoustic, Optical Visualisation, and Laser Diffraction
Colloids Interfaces 2019, 3(4), 65; https://doi.org/10.3390/colloids3040065 - 05 Dec 2019
Abstract
Bubble measurement has been widely discussed in the literature and comparison studies have been widely performed to validate the results obtained for various forms of bubble size inferences. This paper explores three methods used to obtain a bubble size distribution—optical detection, laser diffraction [...] Read more.
Bubble measurement has been widely discussed in the literature and comparison studies have been widely performed to validate the results obtained for various forms of bubble size inferences. This paper explores three methods used to obtain a bubble size distribution—optical detection, laser diffraction and acoustic inferences—for a bubble cloud. Each of these methods has advantages and disadvantages due to their intrinsic inference methodology or design flaws due to lack of specificity in measurement. It is clearly demonstrated that seeing bubbles and hearing them are substantially and quantitatively different. The main hypothesis being tested is that for a bubble cloud, acoustic methods are able to detect smaller bubbles compared to the other techniques, as acoustic measurements depend on an intrinsic bubble property, whereas photonics and optical methods are unable to “see” a smaller bubble that is behind a larger bubble. Acoustic methods provide a real-time size distribution for a bubble cloud, whereas for other techniques, appropriate adjustments or compromises must be made in order to arrive at robust data. Acoustic bubble spectrometry consistently records smaller bubbles that were not detected by the other techniques. The difference is largest for acoustic methods and optical methods, with size differences ranging from 5–79% in average bubble size. Differences in size between laser diffraction and optical methods ranged from 5–68%. The differences between laser diffraction and acoustic methods are less, and range between 0% (i.e., in agreement) up to 49%. There is a wider difference observed between the optical method, laser diffraction and acoustic methods whilst good agreement between laser diffraction and acoustic methods. The significant disagreement between laser diffraction and acoustic method (35% and 49%) demonstrates the hypothesis, as there is a higher proportion of smaller bubbles in these measurements (i.e., the smaller bubbles ‘hide’ during measurement via laser diffraction). This study, which shows that acoustic bubble spectrometry is able to detect smaller bubbles than laser diffraction and optical techniques. This is supported by heat and mass transfer studies that show enhanced performance due to increased interfacial area of microbubbles, compared to fine bubbles. Full article
(This article belongs to the Special Issue B&D 2019)
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Open AccessArticle
Automatic Single Droplet Generator with Control over Droplet Size and Detachment Frequency
Colloids Interfaces 2019, 3(3), 57; https://doi.org/10.3390/colloids3030057 - 22 Aug 2019
Abstract
This paper presents a quite simple, fully automatized single droplet generator, which can be an alternative for more expensive and complicated microfluidic devices. The simple generation nozzle connected to the pressure cells and cheap peristaltic pumps, synchronized via developed software with simple GUI [...] Read more.
This paper presents a quite simple, fully automatized single droplet generator, which can be an alternative for more expensive and complicated microfluidic devices. The simple generation nozzle connected to the pressure cells and cheap peristaltic pumps, synchronized via developed software with simple GUI (graphical user interface) implemented into the Raspberry Pi microcomputer allows precise control over the single droplet diameter and detachment frequency. The generator allows the formation of droplets of quite wide range of diameters without the need of orifice diameter replacements. Free control over time available for adsorption of surface active-substances over the surface of immobilized droplet, before its detachment from the orifice, is an advantage of the developed device. Full article
(This article belongs to the Special Issue B&D 2019)
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Review

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Open AccessFeature PaperReview
Contact Angle Profiles for Droplets on Omniphilic Surfaces in the Presence of Tangential Forces
Colloids Interfaces 2019, 3(4), 60; https://doi.org/10.3390/colloids3040060 - 25 Sep 2019
Abstract
In real life, sessile droplets usually have a three-dimensional shape, making it difficult to understand their forced wetting behavior, both from an experimental and a theoretical perspective. Even in the case of spreading under quasi-static conditions, where the droplet shape is described by [...] Read more.
In real life, sessile droplets usually have a three-dimensional shape, making it difficult to understand their forced wetting behavior, both from an experimental and a theoretical perspective. Even in the case of spreading under quasi-static conditions, where the droplet shape is described by the Young–Laplace equation, there is no fundamental approach to describe the contact line evolution. In the present work, a few existing approaches on this issue are analyzed and assessed. It is shown that an experimentally inspired fixed shape for the contact line of droplets that are spreading under the action of tangential forces can be considered equivalent to a theory for contact line motion. There is a lack of experimental data for contact line evolution under arbitrary scenarios of forces. Such data will be very helpful for the further development of the suggested approach to contact line motion. Of particular interest is the case of small contact angle droplets, for which a top view can clearly indicate the contact line location. On the contrary, in such droplets, the direct experimental measurement of contact angle profile is very difficult. This must be estimated theoretically; thus, a special approach has been developed here for this purpose. Full article
(This article belongs to the Special Issue B&D 2019)
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