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Colloids Interfaces, Volume 4, Issue 4 (December 2020) – 13 articles

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Open AccessFeature PaperReview
Advances in Understanding Hydrogel Lubrication
Colloids Interfaces 2020, 4(4), 54; https://doi.org/10.3390/colloids4040054 - 13 Nov 2020
Viewed by 237
Abstract
Since their inception, hydrogels have gained popularity among multiple fields, most significantly in biomedical research and industry. Due to their resemblance to biological tribosystems, a significant amount of research has been conducted on hydrogels to elucidate biolubrication mechanisms and their possible applications as [...] Read more.
Since their inception, hydrogels have gained popularity among multiple fields, most significantly in biomedical research and industry. Due to their resemblance to biological tribosystems, a significant amount of research has been conducted on hydrogels to elucidate biolubrication mechanisms and their possible applications as replacement materials. This review is focused on lubrication mechanisms and covers friction models that have attempted to quantify the complex frictional characteristics of hydrogels. From models developed on the basis of polymer physics to the concept of hydration lubrication, assumptions and conditions for their applicability are discussed. Based on previous models and our own experimental findings, we propose the viscous-adhesive model for hydrogel friction. This model accounts for the effects of confinement of the polymer network provided by a solid surface and poroelastic relaxation as well as the (non) Newtonian shear of a complex fluid on the frictional force and quantifies the frictional response of hydrogels-solid interfaces. Finally, the review delineates potential areas of future research based on the current knowledge. Full article
(This article belongs to the Special Issue Surface Forces, Adhesion, and Friction)
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Open AccessFeature PaperArticle
Impact of Adsorption Layer Properties on Drainage Behavior of Microscopic Foam Films: The Case of Cationic/Nonionic Surfactant Mixtures
Colloids Interfaces 2020, 4(4), 53; https://doi.org/10.3390/colloids4040053 - 13 Nov 2020
Viewed by 217
Abstract
Aqueous mixtures of cationic hexadecyltrimethylammonium chloride (CTAC) and nonionic pentaethyleneglycol monododecyl ether (C12E5) are investigated. Adsorption layer properties are systematically studied within a wide concentration range for a 1:1 molar ratio of the surfactants. Surface tension and dilatational rheology [...] Read more.
Aqueous mixtures of cationic hexadecyltrimethylammonium chloride (CTAC) and nonionic pentaethyleneglycol monododecyl ether (C12E5) are investigated. Adsorption layer properties are systematically studied within a wide concentration range for a 1:1 molar ratio of the surfactants. Surface tension and dilatational rheology measurements are conducted by profile analysis tensiometry. The interfacial data are juxtaposed to drainage kinetics and stability results for microscopic foam films, investigated by microinterferometric thin liquid film instrumentation. The obtained results give experimental evidence of synergistic interactions in the studied solutions, as compared to the corresponding single surfactant systems. Specific runs of dynamic and equilibrium surface tension curves are registered against the total surfactant quantity; the surface dilatational elasticities for the mixtures are systematically higher. A clear correlation is established between adsorption layer performance and foam film characteristics. The maxima of the film lifetimes are well outlined, and the respective values are shifted towards lower overall concentrations. The reported results substantiate the key role of the adsorption layers, and the surface dilatational properties in particular, for foam film drainage kinetics and stability. The well-expressed synergy observed in adsorption layer and foam film properties suggests the substantial benefits of using mixed surfactant systems in the design and fine-tuning of foam systems for innovative applications. Full article
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Open AccessArticle
Heteroaggregation and Homoaggregation of Latex Particles in the Presence of Alkyl Sulfate Surfactants
Colloids Interfaces 2020, 4(4), 52; https://doi.org/10.3390/colloids4040052 - 13 Nov 2020
Viewed by 229
Abstract
Heteroaggregation and homoaggregation is investigated with time-resolved multi-angle dynamic light scattering. The aggregation rates are measured in aqueous suspensions of amidine latex (AL) and sulfate latex (SL) particles in the presence of sodium octyl sulfate (SOS) and sodium dodecyl sulfate (SDS). As revealed [...] Read more.
Heteroaggregation and homoaggregation is investigated with time-resolved multi-angle dynamic light scattering. The aggregation rates are measured in aqueous suspensions of amidine latex (AL) and sulfate latex (SL) particles in the presence of sodium octyl sulfate (SOS) and sodium dodecyl sulfate (SDS). As revealed by electrophoresis, the surfactants adsorb to both types of particles. For the AL particles, the adsorption of surfactants induces a charge reversal and triggers fast aggregation close to the isoelectric point (IEP). The negatively charged SL particles remain negatively charged and stable in the whole concentration range investigated. The heteroaggregation rates for AL and SL particles are fast at low surfactant concentrations, where the particles are oppositely charged. At higher concentrations, the heteroaggregation slows down above the IEP of the AL particles, where the particles become like-charged. The SDS has higher affinity to the surface compared to the SOS, which induces a shift of the IEP and of the fast aggregation regime to lower surfactant concentrations. Full article
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Open AccessArticle
Microparticle Deposition on Human Serum Albumin Layers: Unraveling Anomalous Adsorption Mechanism
Colloids Interfaces 2020, 4(4), 51; https://doi.org/10.3390/colloids4040051 - 05 Nov 2020
Viewed by 257
Abstract
Human serum albumin (HSA) layers are adsorbed on mica under controlled diffusion transport at pH 3.5 and various ionic strengths. The surface concentration of HSA is directly determined by AFM imaging of single molecules. It is shown that the adsorption kinetics derived in [...] Read more.
Human serum albumin (HSA) layers are adsorbed on mica under controlled diffusion transport at pH 3.5 and various ionic strengths. The surface concentration of HSA is directly determined by AFM imaging of single molecules. It is shown that the adsorption kinetics derived in this way is quantitatively described using the random sequential (RSA) adsorption model. The electrokinetic characteristics of the HSA layers at various pHs comprising their zeta potential are acquired in situ while using the streaming potential method. It is shown that at pH 3.5 the zeta potential of mica becomes positive for HSA concentrations above 3000 μm−2. At larger pHs, HSA layers exhibit negative zeta potential for the entire range of coverage. Thorough characteristics of these monolayers at various pHs were performed applying the colloid deposition method involving negatively charged polystyrene microparticles. The kinetics of their deposition and their maximum coverage are determined as a function of the HSA layer surface concentration, pH, and ionic strength. An anomalous deposition of microparticles on substrates also exhibiting a negative zeta potential is observed, which contradicts the Derjaguin, Landau, Vervey, Overbeek (DLVO) theory. This effect is interpreted in terms of heterogeneous charge distribution that results from molecule concentration fluctuations. It is also shown that the maximum concentration of microparticles abruptly decreases with the electric double-layer thickness that is regulated by changing ionic strength, which indicates that their deposition is governed by electrostatic interactions. One can argue that the results obtained in this work can be exploited as useful reference data for the analysis of deposition phenomena of bioparticles on protein layers. Full article
(This article belongs to the Special Issue Outstanding Scientists in Colloids and Interfaces: Emil Chibowski)
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Open AccessArticle
Concentration and Dilution of Ultrafine Bubbles in Water
Colloids Interfaces 2020, 4(4), 50; https://doi.org/10.3390/colloids4040050 - 05 Nov 2020
Viewed by 287
Abstract
Submicron-sized bubbles are now officially called ultrafine bubbles (UFBs) by the international standard. The concentration of UFBs is generally low (<109 particles/mL; <0.001 vol%) compared to other colloidal dispersions. To overcome this practical problem, we concentrated UFBs in ultrapure water prepared by [...] Read more.
Submicron-sized bubbles are now officially called ultrafine bubbles (UFBs) by the international standard. The concentration of UFBs is generally low (<109 particles/mL; <0.001 vol%) compared to other colloidal dispersions. To overcome this practical problem, we concentrated UFBs in ultrapure water prepared by a commercial UFB generator and quantified the effect of rotary evaporation of the dispersion media on the stability of UFBs. The UFB dispersions were characterized by a particle tracking analysis (PTA) instrument. The experimental results showed that the UFBs can be diluted and concentrated without changing the size distribution and there was little or no loss of UFBs. By using a rotary evaporator, UFB dispersions were about 30-fold concentrated and the resultant number concentration reached over 3 × 1010 particles/mL. Increasing the concentration of UFBs allowed for satisfactory dynamic light scattering (DLS) measurements. The differences among the three algorithms for analyzing the raw data, i.e., autocorrelation function, obtained by DLS are discussed, along with the characteristics of the particle size distribution derived from each algorithm. Full article
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Open AccessCommunication
The Effects of Ethanol Concentration and of Ionic Strength on the Zeta Potential of Titania in the Presence of Sodium Octadecyl Sulfate
Colloids Interfaces 2020, 4(4), 49; https://doi.org/10.3390/colloids4040049 - 02 Nov 2020
Viewed by 315
Abstract
Sodium octadecyl sulfate (C18H37SO4Na) induces a negative zeta potential of metal oxides at very low surfactant concentrations as compared with shorter-chained sodium alkyl sulfates. The problem of low solubility of sodium octadecyl sulfate in water was solved [...] Read more.
Sodium octadecyl sulfate (C18H37SO4Na) induces a negative zeta potential of metal oxides at very low surfactant concentrations as compared with shorter-chained sodium alkyl sulfates. The problem of low solubility of sodium octadecyl sulfate in water was solved by the addition of the surfactant to dispersions as ethanolic stock solution, but then the presence of ethanol in dispersions was inevitable. We demonstrate that the concentration of ethanol (up to 5% by mass) in a dispersion containing titania (TiO2) and sodium octadecyl sulfate has an insignificant effect on the zeta potential of particles. We further demonstrate that the shifts in the IEP of titania induced by the presence of sodium octadecyl sulfate are independent of the NaCl concentration. The results obtained in this study can be generalized for 1-1 salts other than NaCl, for metal oxides other than titania, for organic co-solvents other than ethanol, and for sparingly soluble ionic surfactants other than sodium octadecyl sulfate. Full article
(This article belongs to the Special Issue Outstanding Scientists in Colloids and Interfaces: Emil Chibowski)
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Open AccessArticle
Wetting and Evaporation of Solvents on Thin Soluble Substrates
Colloids Interfaces 2020, 4(4), 48; https://doi.org/10.3390/colloids4040048 - 30 Oct 2020
Viewed by 291
Abstract
In this work, the wetting and evaporation behaviour of non-polar solvent droplets on thin soluble coatings is investigated experimentally. The wetting process on spin-coated polymer layers by toluene is captured using shadowgraphy. Initial spontaneous dynamic wetting as well as later stages of wetting [...] Read more.
In this work, the wetting and evaporation behaviour of non-polar solvent droplets on thin soluble coatings is investigated experimentally. The wetting process on spin-coated polymer layers by toluene is captured using shadowgraphy. Initial spontaneous dynamic wetting as well as later stages of wetting are recorded and evaluated. Furthermore, structures obtained by wetting and subsequent evaporation of solvents on polymer coatings are studied by confocal microscopy. The solubility of the substrate has been varied by using polymers with different molecular masses. We observe that initial spreading dynamics does not depend on the molar mass in the studied range. However, we find a strong influence of the molar mass on the late stage wetting dynamics and on the surface structure after solvent evaporation. Full article
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Open AccessFeature PaperArticle
Adsorption of Mixtures of a Pegylated Lipid with Anionic and Zwitterionic Surfactants at Solid/Liquid
Colloids Interfaces 2020, 4(4), 47; https://doi.org/10.3390/colloids4040047 - 29 Oct 2020
Viewed by 270
Abstract
This work explores the association of a pegylated lipid (DSPE-PEG) with different anionic and zwitterionic surfactants (pseudo-binary and pseudo-ternary polymer+ surfactant mixtures), and the adsorption of the polymer + surfactant aggregates onto negatively charged surfaces, with a surface charge density similar to that [...] Read more.
This work explores the association of a pegylated lipid (DSPE-PEG) with different anionic and zwitterionic surfactants (pseudo-binary and pseudo-ternary polymer+ surfactant mixtures), and the adsorption of the polymer + surfactant aggregates onto negatively charged surfaces, with a surface charge density similar to that existing on the damaged hair epicuticle. Dynamic light scattering and zeta potential measurements shows that, in solution, the polymer + surfactant association results from an intricate balance between electrostatic and hydrophobic interactions, which leads to the formation of at least two different types of micellar-like polymer + surfactant aggregates. The structure and physicochemical properties of such aggregates were found strongly dependent on the specific nature and concentration of the surfactant. The adsorption of the polymer + surfactant aggregates onto negatively charged surface was studied using a set of surface-sensitive techniques (quartz crystal microbalance with dissipation monitoring, ellipsometry and Atomic Force Microscopy), which allows obtaining information about the adsorbed amount, the water content of the layers and the topography of the obtained films. Ion-dipole interactions between the negative charges of the surface and the oxyethylene groups of the polymer + surfactant aggregates appear as the main driving force of the deposition process. This is strongly dependent on the surfactant nature and its concentration, with the impact of the latter on the adsorption being especially critical when anionic surfactant are incorporated within the aggregates. This study opens important perspectives for modulating the deposition of a poorly interacting polymer onto negatively charged surfaces, which can impact in the fabrication on different aspects with technological and industrial interest. Full article
(This article belongs to the Special Issue Outstanding Scientists in Colloids and Interfaces: Emil Chibowski)
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Open AccessFeature PaperReview
Cyclosporine CsA—The Physicochemical Characterization of Liposomal and Colloidal Systems
Colloids Interfaces 2020, 4(4), 46; https://doi.org/10.3390/colloids4040046 - 20 Oct 2020
Viewed by 336
Abstract
This paper presents an overview of the possibilities of testing various cyclosporine (CsA) formulations with an emphasis on parameters that may be key to improving the stability and biocompatibility. The feasibility of CsA colloidal systems for oral (injection) administration were investigated using different [...] Read more.
This paper presents an overview of the possibilities of testing various cyclosporine (CsA) formulations with an emphasis on parameters that may be key to improving the stability and biocompatibility. The feasibility of CsA colloidal systems for oral (injection) administration were investigated using different techniques and compared with similar investigations of other researchers. The chosen CsA systems were developed using dipalmitoylphosphocholine (DPPC) and/or cholesterol as a lipid matrix, stabilized with ethanol, with soybean oil or n-tetradecane as oil phase in emulsions, under natural pH, room and physiological temperature. Their integrity was found to be strictly dependent on the stabilizers. The highest CsA penetrability with the system containing phospholipid in the context of its interactions with lipid membranes was shown. Also, the bioavailability of CsA can be enhanced with the biopolymer antibacterial chitosan. This mini-review suggests the suitability of liposome/microemulsion as promising vehicles for CsA delivery. The most hopeful proved to be formulation with the smaller particle size facilitating absorption, but when safety is assessed, relying on just the particle size cannot be the only criteria. Reassumed, the CsA formulation stability known on the basis of the size and zeta potential measurements guarantees a decrease of the individual variations in the drug bioavailability, toxicity and minimizes rejection. Full article
(This article belongs to the Special Issue Outstanding Scientists in Colloids and Interfaces: Emil Chibowski)
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Open AccessArticle
Comparison of Oxalate, Citrate and Tartrate Ions Adsorption in the Hydroxyapatite/Aqueous Electrolyte Solution System
Colloids Interfaces 2020, 4(4), 45; https://doi.org/10.3390/colloids4040045 - 15 Oct 2020
Viewed by 320
Abstract
The kinetics of adsorption/desorption of oxalate, citrate and tartrate anions was investigated using hydroxyapatite from solutions at the initial concentrations of 0.000001 and 0.001 mol/dm3 anions. The adsorption process from a solution with a concentration of 0.001 mol/dm3 takes place in [...] Read more.
The kinetics of adsorption/desorption of oxalate, citrate and tartrate anions was investigated using hydroxyapatite from solutions at the initial concentrations of 0.000001 and 0.001 mol/dm3 anions. The adsorption process from a solution with a concentration of 0.001 mol/dm3 takes place in three stages and is well described by the multiexponential equation of adsorption kinetics. The process of tartrate and citrate ion desorption after increasing the pH to 10 is irreversible, while the oxalate ions undergo significant desorption with the increasing pH. The adsorption of oxalate ions decreases with the increasing pH. This effect is weaker in the adsorption of citrate and tartrate ions. Ion adsorption studies were supplemented with the measurements of zeta potential, FTIR and particle distribution of hydroxyapatite particles. Full article
(This article belongs to the Special Issue Outstanding Scientists in Colloids and Interfaces: Emil Chibowski)
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Open AccessArticle
Electrical Conductivity and Viscosity in Binary Organic Liquid Mixtures: Participation of Molecular Interactions and Nanodomains
Colloids Interfaces 2020, 4(4), 44; https://doi.org/10.3390/colloids4040044 - 14 Oct 2020
Viewed by 313
Abstract
The present work aims to shed light on recent literature reports suggesting that ionic species are implicated in the electrical conductivity of 1-octanol and its mixtures with hydrocarbons. Other workers have questioned this interpretation, and herein, based on new experimentation and with reference [...] Read more.
The present work aims to shed light on recent literature reports suggesting that ionic species are implicated in the electrical conductivity of 1-octanol and its mixtures with hydrocarbons. Other workers have questioned this interpretation, and herein, based on new experimentation and with reference to various literature studies, we consider that molecular interactions are more likely to be responsible. To investigate this, we have studied mixtures of 1-octanol and either silicone oil (SO) or n-dodecane as nonpolar components, using dielectric (in particular electrical conductivity) and viscometric measurements. With reference to the literature, the self-association of alcohols is known to create microheterogeneity in the neat liquids and in mixtures with nonpolar, low dielectric constant liquids, and it has previously been considered to be responsible for the particular solvent properties of alcohols. The present results suggest that the electrical conductivity of alkane/alcohol systems may have similar origins, with percolating pathways formed from octanol-rich nanodomains comprising polar regions containing hydrogen-bonded hydroxyl groups and nonpolar regions dominated by alkyl chains. The percolation threshold found for dodecane/octanol mixtures, in which interactions between the component molecules are found from viscosity measurements to be repulsive, agrees well with results from experimental and theoretical studies of disordered arrangements of packed spheres, and moreover, it is consistent with other published alkane/alcohol results. On the other hand, the situation is more complex for SO/octanol mixtures, in which interactions between the two components are attractive, based on viscosity data, and in which the phase separation of SO occurs at high octanol concentrations. Overall, we have concluded that electrical conductivity in octanol (and potentially all liquid alcohols) and its mixtures with nonpolar molecules, such as alkanes, is consistent with the presence of conducting networks comprising octanol-rich nanodomains formed by self-association, and not as a result of ionic conduction. Full article
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Open AccessArticle
Preparation and Evaluation of Rebamipide Colloidal Nanoparticles Obtained by Cogrinding in Ternary Ground Mixtures
Colloids Interfaces 2020, 4(4), 43; https://doi.org/10.3390/colloids4040043 - 06 Oct 2020
Viewed by 314
Abstract
Aphthous stomatitis is one of the side effects of chemotherapy and radiotherapy in cancer treatment. Rebamipide (RB) mouthwash for stomatitis acts as a radical scavenger. However, RB is poorly soluble in water, which leads to aggregation and precipitation of the dispersoid. The particle [...] Read more.
Aphthous stomatitis is one of the side effects of chemotherapy and radiotherapy in cancer treatment. Rebamipide (RB) mouthwash for stomatitis acts as a radical scavenger. However, RB is poorly soluble in water, which leads to aggregation and precipitation of the dispersoid. The particle size of the drug needs to be less than 100 nm for the particles to reach the mucus layer in the oral cavity. In this study, we attempted to prepare nanoparticles of RB by cogrinding with polyvinylpyrrolidone (PVP) or hydroxypropyl cellulose (HPC) and sodium dodecyl sulfate (SDS) using a mixer ball mill, and evaluated the physicochemical properties of RB nanoparticles, the stability of dispersion in water, and permeation of the mucus layer in vitro. By cogrinding, the particle size decreased to around 110 nm, and powder X-ray diffraction (PXRD) of the particles showed totally broad halo patterns, which suggested a decreased crystalline region. Furthermore, the solubility of RB nanoparticles increased by approximately fourfold compared with RB crystals, and the water dispersibility and permeation of the mucus layer were improved. The results suggest that in a ternary ground mixture of RB, PVP or HPC, and SDS, the RB nanoparticles obtained can be applied as a formulation for stomatitis. Full article
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Open AccessReview
Carbon Nanoparticles and Materials on Their Basis
Colloids Interfaces 2020, 4(4), 42; https://doi.org/10.3390/colloids4040042 - 25 Sep 2020
Viewed by 395
Abstract
Carbon nanoparticles (CNPs) are novel nanostructures with luminescent properties. The development of CNPs involves the elaboration of various synthetic methods, structure characterization, and different applications. However, the problems associated with the CNP structure definition and properties homogeneity are not solved and barely described [...] Read more.
Carbon nanoparticles (CNPs) are novel nanostructures with luminescent properties. The development of CNPs involves the elaboration of various synthetic methods, structure characterization, and different applications. However, the problems associated with the CNP structure definition and properties homogeneity are not solved and barely described in depth. In this feature article, we demonstrate the approaches for the effective separation and purification of CNPs by size and size/charge ratio. We propose a promising way for the synthesis of the uniform-size structures by the application of calcium carbonate porous microparticles as reactors with defined size. Additionally, the application of the CNPs agglomerates for controllable release systems triggered by light and in-situ synthesis of fluorescent conductive carbonaceous films on the base of polyelectrolyte multilayers are under consideration. Full article
(This article belongs to the Special Issue Colloidal Systems: Formation and Applications of Nanomaterials)
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