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Thin Liquid Films and Dispersed Systems–from Fundamentals to Applications
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Thin Liquid Films and Dispersed Systems–from Fundamentals to Applications

A special issue of Coatings (ISSN 2079-6412). This special issue belongs to the section "Liquid–Fluid Coatings, Surfaces and Interfaces".

Deadline for manuscript submissions: closed (31 January 2021) | Viewed by 19701

Special Issue Editor

Dr. Stoyan Karakashev

E-Mail Website
Guest Editor
Department of Natural Sciences, Shumen University "Episkop Konstantin Preslavsky", 117, Universitetska Str. 117, Shumen, Bulgaria
Interests: thin liquid films; wetting; foams; emulsions; ion-specific effects; surfactants; smart systems
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Thin liquid films control the stability of foams, emulsions, and suspensions as their basic structural units. Flotation froths and other complex fluids used in the industry depend significantly on the wetting films between the particles and the bubbles/oil droplets. The rheological behavior of food colloids and blood stream depends on the stability of the thin liquid films between the soft particles. Therefore, this Special Issue aims at covering all the fundamental and industrial aspects related to thin liquid films, foams, emulsions, and complex fluids.

Specifically, the issue will cover works on:

  • Surfaces forces in thin liquid films;
  • Hydrodynamics of thin liquid films;
  • Capillary phenomena in thin liquid films;
  • Ion-specific effects in thin liquid films;
  • Thin wetting films and wetting phenomena;
  • Surfactant adsorption layers;
  • Foam drainage and rheology of foams;
  • “Smart” foams and emulsions;
  • Industrial and medical applications of complex fluids based on thin liquid films.

Thus designed, the Special Issue aims at introducing the readers to the fundamentals of the thin liquid films, foams, and emulsions and their industrial applications.

Dr. Stoyan Karakashev
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. Coatings is an international peer-reviewed open access monthly 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 2600 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

  • Thin liquid films
  • Foams and emulsions
  • Surface phenomena
  • Surface Forces
  • Wetting phenomena
  • Flotation of mineral particles
  • Industrial applications of foams and emulsions

Published Papers (7 papers)

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Research

22 pages, 2859 KiB  
Article
The Law of Parsimony and the Negative Charge of the Bubbles
by Stoyan I. Karakashev and Nikolay A. Grozev
Coatings 2020, 10(10), 1003; https://doi.org/10.3390/coatings10101003 - 20 Oct 2020
Cited by 7 | Viewed by 2662
Abstract
Why the bubbles are negatively charged? This is almost 100 years old question, which many scientists have striven and still are striving to answer using the latest developments of the MD simulations and various physical analytical methods. We scrutinize with this paper the [...] Read more.
Why the bubbles are negatively charged? This is almost 100 years old question, which many scientists have striven and still are striving to answer using the latest developments of the MD simulations and various physical analytical methods. We scrutinize with this paper the basic literature on this topic and conduct our own analysis. Following the philosophical law of parsimony: “Entities should not be multiplied without necessity”, we assume that the simplest explanation is the right one. It is well known that the negative change of the Gibbs free energy is a solid criterion for spontaneous process. Hence, we calculated the energies of adsorption of OH−, H3O+ and HCO3− ions on the air/water interface using the latest theoretical developments on the dispersion interaction of inorganic ions with the air/water interface. Thus, we established that the adsorption of OH− and HCO3− ions is energetically favorable, while the adsorption of H3O+ is energetically unfavorable. Moreover, we calculated the change of the entropy of these ions upon their transfer from the bulk to the air/water interface. Using the well-known formula ΔG = ΔH − TΔS, we established that the adsorption of OH− and HCO3− ions on the air/water interface decreases their Gibbs free energy. On the contrary, the adsorption of H3O+ ions on the air/water interface increases their Gibbs free energy. Thus, we established that both OH− and HCO3− ions adsorb on the air/water interface, while the H3O+ ions are repelled by the latter. Therefore, electrical double layer (EDL) is formed at the surface of the bubble–negatively charged adsorption layer of OH− and HCO3− ions and positively charged diffuse layer of H3O+ ions. Full article
(This article belongs to the Special Issue Thin Liquid Films and Dispersed Systems–from Fundamentals to Applications)
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13 pages, 5740 KiB  
Article
Correlations for Easy Calculation of the Critical Coalescence Concentration (CCC) of Simple Frothers
by Stoyan I. Karakashev, Nikolay A. Grozev, Khandjamts Batjargal, Onur Guven, Orhan Ozdemir, Feridun Boylu and Mehmet Sabri Çelik
Coatings 2020, 10(7), 612; https://doi.org/10.3390/coatings10070612 - 29 Jun 2020
Cited by 7 | Viewed by 2360
Abstract
Can the critical coalescence concentration (CCC) of the flotation frothers be predictable? What is the relation between their molecular structure and their CCC values? A literature survey found specific correlations between the hydrophilic-lipophilic balances (HLB) and HLB/Mw (where Mw stands for the molecular [...] Read more.
Can the critical coalescence concentration (CCC) of the flotation frothers be predictable? What is the relation between their molecular structure and their CCC values? A literature survey found specific correlations between the hydrophilic-lipophilic balances (HLB) and HLB/Mw (where Mw stands for the molecular mass) of homologue series of frothers and their CCC values, but the results are invalid when the molecule’s functional groups change. For this reason, 37 frothers with known values of CCC were analyzed. The CCC values of seven frothers were determined, and the rest were taken from the literature. The frothers were subdivided in homologue series with an increasing number of the carbon atoms with an account for the type and the location of the functional group, thus deriving three types of correlations lnCCC = f(HLB) applicable for: (i) alcohols; (ii) propylene glycols alkyl ethers and propylene glycols; (iii) ethylene glycols alkyl ethers. The average accuracy of these correlations between CCC and HLB is 93%. Full article
(This article belongs to the Special Issue Thin Liquid Films and Dispersed Systems–from Fundamentals to Applications)
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5 pages, 1026 KiB  
Communication
Nonuniform Slip Effect in Wetting Films
by Roumen Tsekov
Coatings 2020, 10(6), 597; https://doi.org/10.3390/coatings10060597 - 25 Jun 2020
Cited by 1 | Viewed by 1945
Abstract
The slip effect in wetting films is theoretically studied, and a nonlinear dependence of the hydrodynamic velocity on the slip length is discovered. It is demonstrated that the hydrodynamic flow is essentially affected by the presence of a nonuniform slip length distribution, leading [...] Read more.
The slip effect in wetting films is theoretically studied, and a nonlinear dependence of the hydrodynamic velocity on the slip length is discovered. It is demonstrated that the hydrodynamic flow is essentially affected by the presence of a nonuniform slip length distribution, leading also to enhancement of the energy dissipation in the films. This effect could dramatically slow the usually quick hydrodynamic flows over superhydrophobic surfaces, for instance. Full article
(This article belongs to the Special Issue Thin Liquid Films and Dispersed Systems–from Fundamentals to Applications)
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14 pages, 3125 KiB  
Article
Investigation of Interfacial Free Energy of Three-Phase Contact on a Glass Sphere in Case of Cationic-Anionic Surfactant Aqueous Mixtures
by Lidia A. Alexandrova, Ljudmil S. Grigorov, Nikolay A. Grozev and Stoyan I. Karakashev
Coatings 2020, 10(6), 573; https://doi.org/10.3390/coatings10060573 - 18 Jun 2020
Cited by 3 | Viewed by 3036
Abstract
The wetting of adsorbed surfactants solids is important for various technological applications in particular for the process of foam flotation. The present work aims at calculating the surface tensions of the three phase interfaces at different surfactant concentrations using the Girifalco and Good [...] Read more.
The wetting of adsorbed surfactants solids is important for various technological applications in particular for the process of foam flotation. The present work aims at calculating the surface tensions of the three phase interfaces at different surfactant concentrations using the Girifalco and Good method. For this purpose, the surface tension and contact angle vs. surfactant concentration of the test substances amines and sulfonates and their mixture were measured for liquid–air interface. Calculated surface tension of solid–air interface vs. concentration for C10 amine and mixed systems are close to those for the liquid–air surface, but are slightly lower. In the case of mixed systems, the graph has a specific structure similar to that of liquid–air surface dependence. In contrast to the solid–air interface results, the solid–liquid surface tension values are significantly lower. In case of the mixed surfactant systems, C10amine/C10 sulfonate, a synergetic effect on the surface tension is observed. The specific behavior of the mixed systems is interpreted with the emergence of aggregates consisting of the anionic and cationic surfactants. It is shown that in the whole area of concentrations complete wetting does not occur. Full article
(This article belongs to the Special Issue Thin Liquid Films and Dispersed Systems–from Fundamentals to Applications)
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16 pages, 3121 KiB  
Article
Foam Formation and Interaction with Porous Media
by Phillip Johnson, Mauro Vaccaro, Victor Starov and Anna Trybala
Coatings 2020, 10(2), 143; https://doi.org/10.3390/coatings10020143 - 5 Feb 2020
Cited by 5 | Viewed by 3358
Abstract
Foams are a common occurrence in many industries and many of these applications require the foam to interact with porous materials. For the first time interaction of foams with porous media has been investigated both experimentally and theoretically by O. Arjmandi-Tash et al. [...] Read more.
Foams are a common occurrence in many industries and many of these applications require the foam to interact with porous materials. For the first time interaction of foams with porous media has been investigated both experimentally and theoretically by O. Arjmandi-Tash et al. It was found that there are three different regimes of the drainage process for foams in contact with porous media: rapid, intermediate and slow imbibition. Foam formation using soft porous media has only been investigated recently, the foam was made using a compression device with soft porous media containing surfactant solution. During the investigation, it was found that the maximum amount of foam is produced when the concentration of the foaming agent (dishwashing surfactant) is in the range of 60–80% m/m. The amount of foam produced was independent of the pore size of the media in the investigated range of pore sizes. This study is expanded using sodium dodecyl sulphate (SDS), which has the same critical micelle concentration as the commercial dishwashing surfactant, where the foam is formed using the same porous media and compression device. During the investigation, it was found that 10 times the critical micelle concentration (CMC) is the optimum concentration for a pure SDS surfactant solution to create foam. Any further increase in concentration after that point resulted in no further mass of foam being generated. Full article
(This article belongs to the Special Issue Thin Liquid Films and Dispersed Systems–from Fundamentals to Applications)
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17 pages, 6462 KiB  
Article
Coating Mechanism of AuNPs onto Sepiolite by Experimental Research and MD Simulation
by Deniz Karataş, Dilek Senol Arslan, Ilgin Kursun Unver and Orhan Ozdemir
Coatings 2019, 9(12), 785; https://doi.org/10.3390/coatings9120785 - 22 Nov 2019
Cited by 6 | Viewed by 2944
Abstract
The amenability of gold nanoparticles (AuNPs) coating on natural and modified (hexadecyl trimethyl ammonium bromide, CTAB) sepiolite surfaces was studied both experimentally and theoretically. The zeta potential experiments and Fourier transform infrared spectrophotometer (FTIR), environmental scanning electron microscope (ESEM), and transmission electron microscopy [...] Read more.
The amenability of gold nanoparticles (AuNPs) coating on natural and modified (hexadecyl trimethyl ammonium bromide, CTAB) sepiolite surfaces was studied both experimentally and theoretically. The zeta potential experiments and Fourier transform infrared spectrophotometer (FTIR), environmental scanning electron microscope (ESEM), and transmission electron microscopy (TEM) analyses were carried out with the sepiolite samples in the presence of AuNPs. In addition, the adsorption of three gold-nanoparticles on the sepiolite surface (100) in the absence and presence of CTAB was investigated by molecular dynamics (MD) simulations. The AuNPs showed no significant change in the zeta potential of natural sepiolite surfaces due to negative charges of both the sepiolite and AuNPs at natural pH. The surface charge of modified sepiolite decreased with the increase in AuNPs concentration indicating the significance AuNPs adsorption. FTIR, ESEM, and TEM analyses indicated the coating of AuNPs onto the modified sepiolite surface were higher than that of the natural sepiolite surface. The MD simulation results showed that AuNPs can easily adsorb onto the basal surface of the sepiolite due to its hydrophilicity in the presence and absence of CTAB as indicated in the experimental studies. In short, the modification of sepiolite with CTAB made the charge positive, and in turn considerably increased the AuNPs coating on sepiolite surfaces due to electrostatic attraction. Full article
(This article belongs to the Special Issue Thin Liquid Films and Dispersed Systems–from Fundamentals to Applications)
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13 pages, 1089 KiB  
Article
Influence of the Hamaker Constant on the Value of the Critical Thickness of Foam Films
by Dilyana Ivanova-Stancheva
Coatings 2019, 9(9), 576; https://doi.org/10.3390/coatings9090576 - 10 Sep 2019
Cited by 1 | Viewed by 2816
Abstract
The aim of the present study was to check the influence of the Hamaker constant (A(h)) on the calculated critical thickness of foam films. It was done by a comparison between the experimental data of the critical thickness and the theoretically obtained data [...] Read more.
The aim of the present study was to check the influence of the Hamaker constant (A(h)) on the calculated critical thickness of foam films. It was done by a comparison between the experimental data of the critical thickness and the theoretically obtained data with different values of (A(h)), which take part in the equations of Radoev, Scheludko, Manev, and Vrij. We calculated the latter for film thicknesses from 15 to 70 nm based on several equations. We used the experimental data of hcr (average value of critical thickness and measured once, in the place of a spot appearance) for foam films stabilized by non-ionic surfactant n-dodecyl-β-D-maltoside (C12G2) or by cationic surfactant n-dodecyl trimethylammonium bromide (C12TAB), as measured by the interferometric method. The foam films were produced from solutions with surfactant concentration at CMC (Critical Micelle Concentration) in the presence of 0.1 M NaBr. For films of C12G2, the best correspondence was found between measured hcr (in the spot) and calculated ones by the RShM equation using effective A(h) (introduced by Coons et al.) or Vassilieff’s values, but with a correction for the added electrolyte. For films stabilized by C12TAB, a difference between the measured and theoretically calculated hcr was found, which was probably due to the nature of the surfactant. Nevertheless, this difference was smallest when calculated hcr values were obtained with data for Aeff (h) and Vassilieff’s A(h) constant, respectively. Full article
(This article belongs to the Special Issue Thin Liquid Films and Dispersed Systems–from Fundamentals to Applications)
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