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Colloids Interfaces, Volume 6, Issue 4 (December 2022) – 25 articles

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Article
Green Synthesis of Antibacterial Silver Nanocolloids with Agroindustrial Waste Extracts, Assisted by LED Light
Colloids Interfaces 2022, 6(4), 74; https://doi.org/10.3390/colloids6040074 - 01 Dec 2022
Viewed by 128
Abstract
Herein, the green synthesis of silver nanoparticles (AgNPs), assisted by LED light, using the aqueous extracts of agroindustrial waste products, such as avocado seeds (ASs), cocoa pod husks (CPHs), and orange peels (OPs), is presented. Surface plasmon resonance analysis showed faster and complete [...] Read more.
Herein, the green synthesis of silver nanoparticles (AgNPs), assisted by LED light, using the aqueous extracts of agroindustrial waste products, such as avocado seeds (ASs), cocoa pod husks (CPHs), and orange peels (OPs), is presented. Surface plasmon resonance analysis showed faster and complete NP formation when irradiated with blue LED light. Green and red light irradiation showed non- and limited nanoparticle formation. TEM analyses confirmed the semispherical morphology of the synthesized AgNPs, with the exception of OP–AgNPs, which showed agglomeration during the light irradiation. For AS–AgNPs and CPH–AgNPs, the average particle diameter was about 15 nm. Interestingly, the CPH extract demonstrated faster nanoparticle formation as compared to the AS extract (100 min vs. 250 min irradiation time, respectively). FTIR spectroscopy assessed the involvement of diverse functional groups of the bioactive phytochemicals present in the plant extracts during nanoparticle photobiosynthesis. The antioxidant activity, as determined by ferric reducing antioxidant power (FRAP) assay, varied from 1323.72 µmol TE/mL in the AS aqueous extract to 836.50 µmol TE/mL in the CPH aqueous extract. The total polyphenol content was determined according to the Folin–Ciocalteu procedure; the AS aqueous extract exhibited a higher polyphenol content (1.54 mg GAE/g) than did the CPH aqueous extract (0.948 mg GAE/g). In vitro antibacterial assays revealed that the AS–AgNPs exhibited promising antibacterial properties against pathogenic bacteria (E. Coli), whereas the CPH–AgNPs showed antibacterial activity against S. aureus and E. coli. The green synthesis of AgNPs using AS, CPH, and OP aqueous extracts reported in this work is environmentally friendly and cost-effective, and it paves the way for future studies related to agroindustrial waste valorization for the production of advanced nanomaterials, such as antibacterial AgNPs, for potential biomedical, industrial, and environmental applications. Full article
(This article belongs to the Special Issue Biocolloids and Biointerfaces)
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Article
Remarkable Separation of Carbofuran Pesticide from Aqueous Solution Using Free Metal Ion Variation on Aluminum-Based Metal-Organic Framework
Colloids Interfaces 2022, 6(4), 73; https://doi.org/10.3390/colloids6040073 - 28 Nov 2022
Viewed by 268
Abstract
The alarming increase in pesticide residues poses a major threat to aquatic and natural habitats. Therefore, it has become essential to design extremely operationally and economically advantageous systems for the removal of carbofuran pesticides from wastewater. Here, an aluminum-based metal-organic framework (MOF), MIL-53-NH [...] Read more.
The alarming increase in pesticide residues poses a major threat to aquatic and natural habitats. Therefore, it has become essential to design extremely operationally and economically advantageous systems for the removal of carbofuran pesticides from wastewater. Here, an aluminum-based metal-organic framework (MOF), MIL-53-NH2, and its modified forms, MIL-53-NH-ph, MIL-53-NH-ph-Fe, MIL-53-NH-ph-Zn, and MIL-53-NH-ph-Cu, have been successfully synthesized. Full characterization using IR, 1HNMR, XRD, and SEM was carried out. The prepared MOFs have been utilized as effective adsorbents for carbofuran in aqueous solutions. The various factors affecting the adsorption process (pH, time, and adsorbate concentration) were also investigated. Spectroscopic approaches were used to investigate the adsorption mechanisms. A mixture of π-π stacking contact, coordination bonding, and hydrogen bond formation can be connected to the current process. The adsorption of carbofuran from aqueous solutions was best described by pseudo-second-order kinetics and Langmuir equilibrium isotherm models. MIL-53-NH2, MIL-53-NH-Ph, MIL-53-NH-Ph-Fe, MIL-53-NH-Ph-Zn, and MIL-53-NH-Ph-Cu demonstrated adsorption capacities of 367.8, 462.1, 662.94, 717.6, and 978.6 mg g−1, respectively. Full article
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Article
Fabrication of Polystyrene/AlOOH Hybrid Material for Pb(II) Decontamination from Wastewater: Isotherm, Kinetic, and Thermodynamic Studies
Colloids Interfaces 2022, 6(4), 72; https://doi.org/10.3390/colloids6040072 - 24 Nov 2022
Viewed by 192
Abstract
The nanomaterials’ toxicity to aquatic life is a big issue due to improper handling or incomplete separation after use. The immobilization of the nanomaterials in the polymeric matrix could be a practical approach to developing an efficient hybrid composite for wastewater purification. In [...] Read more.
The nanomaterials’ toxicity to aquatic life is a big issue due to improper handling or incomplete separation after use. The immobilization of the nanomaterials in the polymeric matrix could be a practical approach to developing an efficient hybrid composite for wastewater purification. In this study, AlOOH nanoparticles were immobilized in the polystyrene polymeric matrix to prepare an effective adsorbent to scavenge the Pb(II) from the aqueous solution. The synthesized polystyrene/AlOOH (PS/AlOOH) hybrid was characterized using microscopic techniques coupled with elemental mapping and EDX, X-ray diffraction, and a furrier-transformed infrared spectrometer. The results revealed that the Pb(II) adsorption onto the polystyrene/AlOOH composite depends on the solution pH, the Pb(II) concentrations in the solution, the adsorption time, and the solute temperature. The maximum scavenging of Pb(II) occurs at pH 6 in 90 min. The adsorption of Pb(II) onto PS/AlOOH decreases from 97.7% to 58.5% with the increase in the Pb(II) concentration from 20 mg g−1 to 100 mg g−1. The kinetics and isotherm modeling demonstrated that Pb(II) adsorption is well suited for the pseudo-second-order kinetics and Toth isotherm models, suggesting that the chemisorption occurs at the heterogeneous surface of PS/AlOOH. The PS/AlOOH composite could be used multiple times without a significant loss in the adsorption efficiency. These results demonstrated that the polystyrene/AlOOH composite is an effective material for the purification of wastewater and can be used on a large scale. Full article
(This article belongs to the Special Issue Colloids Science in Asia)
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Article
Emulsifiers from White Beans: Extraction and Characterization
Colloids Interfaces 2022, 6(4), 71; https://doi.org/10.3390/colloids6040071 - 21 Nov 2022
Viewed by 308
Abstract
This paper studies the emulsification capacity of aqueous extracts from white beans and reports the relations between the composition and structure of the extracts’ macromolecular components and their exerted emulsification ability. The extracts comprise of three distinct populations: one of large (few MDa) [...] Read more.
This paper studies the emulsification capacity of aqueous extracts from white beans and reports the relations between the composition and structure of the extracts’ macromolecular components and their exerted emulsification ability. The extracts comprise of three distinct populations: one of large (few MDa) polysaccharides, proteins (tens of kDa), and smaller molecular entities (oligopeptides and oligosaccharides, polyphenols, and salts, among other molecules); the proteins and the smaller molecules adsorb onto oil–water interfaces, providing some emulsification capacity at pH 3 and adequate emulsification at pH 7. Unabsorbed polysaccharides, such as starch, cause depletion flocculation. Pickering phenomena are involved in the stabilization mechanism. The findings are supported by SEC–MALLS/UV, confocal microscopy, zeta potential measurements, and FT–IR data. A discussion is made on the particular attributes of each population in emulsion stability, on their relevance to culinary practice, and in their potential as replacers of artificial emulsifiers. Full article
(This article belongs to the Special Issue Food Colloids II)
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Article
Addition of Trans-Resveratrol-Loaded, Highly Concentrated Double Emulsion to Moisturizing Cream: Effect on Physicochemical Properties
Colloids Interfaces 2022, 6(4), 70; https://doi.org/10.3390/colloids6040070 - 16 Nov 2022
Viewed by 261
Abstract
Resveratrol is a compound increasingly studied for its many beneficial properties for health. However, it is a highly unstable photosensitive compound, and therefore it is necessary to encapsulate it to protect it if you want to use it in a commercial product. Emulsions [...] Read more.
Resveratrol is a compound increasingly studied for its many beneficial properties for health. However, it is a highly unstable photosensitive compound, and therefore it is necessary to encapsulate it to protect it if you want to use it in a commercial product. Emulsions are systems that allow the encapsulation of active ingredients, protecting them and allowing their release in a controlled manner. They are highly used systems in the pharmaceutical, cosmetic and food industries. The main objectives of this work are to study the feasibility of encapsulating resveratrol in concentrated water-in-oil-in-water double emulsions and the effect produced by adding the double emulsion with optimal formulation to a commercial cream for cosmetic applications. The effect of the selected optimal double emulsion on a commercial cream was studied, analyzing droplet size distribution, morphology, stability and rheology. The main conclusion of this work is that incorporating 1/3 of concentrated double emulsion W1/O/W2 into a commercial moisturizing cream had a positive physical effect and produced cream with a resveratrol concentration of up to 0.0042 mg/g. Full article
(This article belongs to the Special Issue Recent Advances in Emulsions and Applications)
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Article
Can Enzymatic Treatment of Sugar Beet Pectins Reduce Coalescence Effects in High-Pressure Processes?
Colloids Interfaces 2022, 6(4), 69; https://doi.org/10.3390/colloids6040069 - 15 Nov 2022
Viewed by 279
Abstract
While sugar beet pectins (SBPs) are well known for effectively stabilizing fine oil droplets in low-fat food and beverages, e.g., low-fat dressings and soft drinks, it often fails in products of higher oil contents. The aim of this study was to improve the [...] Read more.
While sugar beet pectins (SBPs) are well known for effectively stabilizing fine oil droplets in low-fat food and beverages, e.g., low-fat dressings and soft drinks, it often fails in products of higher oil contents. The aim of this study was to improve the emulsifying properties of SBPs and, consequently, their ability to reduce coalescence during high pressure homogenization of products with increased oil content. Therefore, the molecular size of SBPs was reduced by partial cleavage of the homogalacturonan backbone using the enzymes exo- and endo-polygalacturonanase and varying incubation times. The sizes of SBPs were compared based on the molecular size distribution and hydrodynamic diameter. In addition, to obtain information on the interfacial activity and adsorption rate of SBPs, the dynamic interfacial tension was measured by drop profile analysis tensiometry. The (non)modified SBPs were used as emulsifying agents in 30 wt% mct oil–water emulsions stabilized with 0.5 wt% SBP at pH 3, prepared by high-pressure homogenization (400–1000 bar). By analyzing the droplet size distributions, conclusions could be drawn about the coalescence that occurred after droplet breakup. It could be shown that SBPs modified by exo-polygalacturonanase stabilized the oil–water interface more rapidly, resulting in less coalescence and the smallest oil droplets. In contrast, SBPs modified with endo-polygalacturonanase resulted in poorer emulsification properties, and thus larger oil droplets with increasing incubation time. The differences could be attributed to the different cleavage pattern of the enzymes used. The results suggest that a minimum molecular size is required for the stabilization of fine oil droplets with SBPs as emulsifiers. Full article
(This article belongs to the Special Issue Food Colloids II)
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Article
Direct Resolution of the Interactions of a Hydrocarbon Gas with Adsorbed Surfactant Monolayers at the Water/Air Interface Using Neutron Reflectometry
Colloids Interfaces 2022, 6(4), 68; https://doi.org/10.3390/colloids6040068 - 14 Nov 2022
Viewed by 256
Abstract
We have directly resolved in the present work the interfacial composition during and after the interactions of a saturated atmosphere of oil vapor with soluble surfactant solutions at a planar water/air interface for the first time. Experiments were conducted on interactions of hexane [...] Read more.
We have directly resolved in the present work the interfacial composition during and after the interactions of a saturated atmosphere of oil vapor with soluble surfactant solutions at a planar water/air interface for the first time. Experiments were conducted on interactions of hexane vapor with solutions of alkyltrimethylammonium bromides and sodium dodecyl sulfate to observe the balance between cooperativity and competition of the components at the interface. In all cases, hexane adsorption was strongly enhanced by the presence of the surfactant, even at bulk surfactant concentrations four orders of magnitude below the critical micelle concentration. Cooperativity of the surfactant adsorption was observed only for sodium dodecyl sulfate at intermediate bulk concentrations, yet for all four systems, competition set in at higher concentrations, as hexane adsorption reduced the surfactant surface excess. The data fully supported the complete removal of hexane from the interface following venting of the system to remove the saturated atmosphere of oil vapor. These results help to identify future experiments that would elaborate and could explain the cooperativity of surfactant adsorption, such as on cationic surfactants with short alkyl chains and a broader series of anionic surfactants. This work holds relevance for oil recovery applications with foam, where there is a gas phase saturated with oil vapor. Full article
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Article
Thermoresponsive Starch Nanoparticles for the Extraction of Bitumen from Oil Sands
Colloids Interfaces 2022, 6(4), 67; https://doi.org/10.3390/colloids6040067 - 09 Nov 2022
Viewed by 431
Abstract
Starch nanoparticles (SNPs) useful for the extraction of bitumen from oil sands were obtained by modification with thermoresponsive poly(di(ethylene glycol) methyl ether methacrylate) (PMEO2MA) segments through RAFT (Reversible Addition–Fragmentation chain Transfer) grafting. Since PMEO2MA exhibits a Lower Critical Aggregation [...] Read more.
Starch nanoparticles (SNPs) useful for the extraction of bitumen from oil sands were obtained by modification with thermoresponsive poly(di(ethylene glycol) methyl ether methacrylate) (PMEO2MA) segments through RAFT (Reversible Addition–Fragmentation chain Transfer) grafting. Since PMEO2MA exhibits a Lower Critical Aggregation Temperature (LCAT), the polymer-grafted SNPs are amphiphilic above the LCAT of the thermoresponsive polymer and can interact efficiently with bitumen in the oil sands, facilitating its extraction. The PMEO2MA-grafted SNPs form micellar aggregates that remain dispersed in water but can shuttle the bitumen component out of the sand and silt mixture in the extraction process above the LCAT. Upon cooling, the hydrophobic PMEO2MA domains become hydrophilic again and the grafted SNPs remain in the water phase, while the extracted oil floats on the aqueous phase and can be skimmed off. The aqueous polymer solution may be reused in other extraction cycles. Extraction by tumbling of the oil-water-SNP mixtures in vials at 45 °C reached over 80% efficiency. The synthetic methods used provide easy control over the characteristics of the grafted SNPs (number and length of grafted PMEO2MA segments), and therefore over their hydrophilic-lipophilic balance (HLB). The SNP-g-PMEO2MA samples were characterized by 1H NMR, UV-visible spectroscopy and dynamic light scattering analysis, and the grafted PMEO2MA chains were cleaved from the starch substrates for analysis by gel permeation chromatography. Full article
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Article
Turning a Novel Janus Electrospun Mat into an Amphiphilic Membrane with High Aromatic Hydrocarbon Adsorption Capacity
Colloids Interfaces 2022, 6(4), 66; https://doi.org/10.3390/colloids6040066 - 04 Nov 2022
Viewed by 364
Abstract
Aromatic hydrocarbons in water is one of the collateral effects of the petrochemical industry and represents a serious problem both for their toxicity and environmental contamination. In this work, an innovative amphiphilic membrane was developed capable of rapidly removing hydrocarbons (such as BTEX) [...] Read more.
Aromatic hydrocarbons in water is one of the collateral effects of the petrochemical industry and represents a serious problem both for their toxicity and environmental contamination. In this work, an innovative amphiphilic membrane was developed capable of rapidly removing hydrocarbons (such as BTEX) present in water under the solubility limit. Firstly, a Janus nanostructured membrane was developed from the deposition of superhydrophobic carbonaceous nanoparticles (CNPs) synthesized by radiofrequency plasma polymerization on a hydrophilic electrospun poly(vinyl alcohol) mat. Secondly, this membrane was turned amphiphilic by UV exposure, allowing water to pass through. The surface properties of the membranes were studied through SEM, contact angle, and FTIR analysis. Dead-end experiments showed that the toluene and xylene selective sorption capacity reached the outstanding adsorption capacity of 647 mg/g and 666 mg/g, respectively, and that the membrane could be reused three times without efficiency loss. Furthermore, swelling of the PVA fibers prevented the liberation of NPs. The selective sorption capacity of the UV-exposed CNPs was explained by studying the interfacial energy relations between the materials at play. This work provides a simple, low-cost, and scalable technique to develop membranes with great potential for water remediation, including the removal of volatile organic compounds from produced water, as well as separating oil-in-water emulsions. Full article
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Article
Effect of Acyl Chain Length on Hydrophobized Cashew Gum Self-Assembling Nanoparticles: Colloidal Properties and Amphotericin B Delivery
Colloids Interfaces 2022, 6(4), 65; https://doi.org/10.3390/colloids6040065 - 04 Nov 2022
Viewed by 330
Abstract
Given its many potential applications, cashew gum hydrophobic derivatives have gained increasing attraction in recent years. We report here the effect of acyl chain length on hydrophobized cashew gum derivatives, using acetic, propionic, and butyric anhydrides on self-assembly nanoparticle properties and amphotericin B [...] Read more.
Given its many potential applications, cashew gum hydrophobic derivatives have gained increasing attraction in recent years. We report here the effect of acyl chain length on hydrophobized cashew gum derivatives, using acetic, propionic, and butyric anhydrides on self-assembly nanoparticle properties and amphotericin B delivery. Nanoparticles with unimodal particle size distribution, highly negative zeta potential, and low PDI were produced. Butyrate cashew gum nanoparticles presented smaller size (<~100 nm) than acetylated and propionate cashew gum nanoparticles and no cytotoxicity in murine fibroblast cells was observed up to 100 µg/mL for loaded and unloaded nanoparticles. As a proof of concept of the potential use of the developed nanoparticle as a drug carrier formulation, amphotericin B (AmB) was encapsulated and fully characterized in their physicochemical, AmB association and release, stability, and biological aspects. They exhibited average hydrodynamic diameter lower than ~200 nm, high AmB efficiency encapsulations (up to 94.9%), and controlled release. A decrease in AmB release with the increasing of the anhydride chain length was observed, which explains the differences in antifungal activity against Candida albicans strains. An excellent storage colloidal stability was observed for unloaded and loaded AmB without use of surfactant. Considering the AmB delivery, the acyl derivative with low chain length is shown to be the best one, as it has high drug loading and AmB release, as well as low minimum inhibitory concentration against Candida albicans strains. Full article
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Article
Stability Studies and the In Vitro Leishmanicidal Activity of Hyaluronic Acid-Based Nanoemulsion Containing Pterodon pubescens Benth. Oil
Colloids Interfaces 2022, 6(4), 64; https://doi.org/10.3390/colloids6040064 - 03 Nov 2022
Viewed by 399
Abstract
The physicochemical and microbiological stability of a hyaluronic acid-based nanostructured topical delivery system containing P. pubescens fruit oil was evaluated, and the in vitro antileishmanial activity of the nanoemulsion against Leishmania amazonensis and the cytotoxicity on macrophages was investigated. The formulation stored at [...] Read more.
The physicochemical and microbiological stability of a hyaluronic acid-based nanostructured topical delivery system containing P. pubescens fruit oil was evaluated, and the in vitro antileishmanial activity of the nanoemulsion against Leishmania amazonensis and the cytotoxicity on macrophages was investigated. The formulation stored at 5 ± 2 °C, compared with the formulation stored at 30 and 40 ± 2 °C, showed a higher chemical and physical stability during the period analyzed and in the accelerated physical stability study. The formulation stored at 40 °C presented a significant change in droplet diameter, polydispersity index, zeta potential, pH, active compound, and consistency index and was considered unstable. The microbiological stability of the formulations was confirmed. The leishmanicidal activity of the selected system against intracellular amastigotes was significantly superior to that observed for the free oil. However, further research is needed to explore the use of the hyaluronic acid-based nanostructured system containing P. pubescens fruit oil for the treatment of cutaneous leishmaniasis. Full article
(This article belongs to the Special Issue Recent Advances in Emulsions and Applications)
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Article
Experimental Evaluation of Foam Diversion for EOR in Heterogeneous Carbonate Rocks
Colloids Interfaces 2022, 6(4), 63; https://doi.org/10.3390/colloids6040063 - 02 Nov 2022
Viewed by 382
Abstract
Immiscible gas injection applied to heterogeneous carbonate reservoirs can be inefficient due to poor conformance control. Foam mobility control is proposed in this work as a solution for gas conformance issues in such reservoirs. A unique experimental program was developed to evaluate alkyl [...] Read more.
Immiscible gas injection applied to heterogeneous carbonate reservoirs can be inefficient due to poor conformance control. Foam mobility control is proposed in this work as a solution for gas conformance issues in such reservoirs. A unique experimental program was developed to evaluate alkyl polyglucoside (APG) stabilized foam for foaming ability, emulsion-forming tendency and resistance to oil. Dynamic methane foam behavior is systematically studied through single and dual injection core flooding experiments, simulating foam diversion during immiscible methane flooding in a layered reservoir with a significant layer permeability contrast. Results show a stable foam-oil system with no viscous emulsions at very high formation brine salinity (144,000 ppm total dissolved solids). Single-core floods for the high permeability layer (Unit-A) showed that foam viscosity of 27 cP could be achieved at 11% oil saturation (So). Under similar oil-wet condition, the low permeability zone (Unit-B) could generate foam of 21 cP at 18.9% So, indicating an increase in injected fluid mobility reduction with permeability. Dual-core injection experiments, which is designed to evaluate accurately fluid diversion capacity of such foams, reveals remarkable dynamic foam behaviors. While the water-wet condition indicates the scalability of foam behaviors (i.e., the ability of foam to control fluid mobility against the variation of rock permeability) between the single and composite core systems, the oil-wet condition confirms good foam resistance to residual oil that resulted in an increase in Unit B production from 46 to 82%, and 74 to 85% for Unit-A. Moreover, dual-core floods representing premature waterfloods (i.e., higher oil saturation) shows even more dramatic incremental oil recovery (44 to 81% in Unit-A and 17.5 to 71% in Unit-B), evidencing the ability of foam to self-viscosify with permeability variation at varying oil saturations. Full article
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Article
The Viscosity and Self-Diffusion of Some Real Colloidal Ferrofluids
Colloids Interfaces 2022, 6(4), 62; https://doi.org/10.3390/colloids6040062 - 31 Oct 2022
Viewed by 282
Abstract
One primary concern in colloid science is understanding the relationship of its macroscopic rheology and diffusion behavior with the observed microscopic arrangements of the nanoparticles in the fluid. This manuscript addresses the study of these dynamical properties through a first-principle stochastic method. Both [...] Read more.
One primary concern in colloid science is understanding the relationship of its macroscopic rheology and diffusion behavior with the observed microscopic arrangements of the nanoparticles in the fluid. This manuscript addresses the study of these dynamical properties through a first-principle stochastic method. Both properties directly relate to the observed fluid structure factor, which depends on a few known material parameters. However, in the literature, this static quantity is reported up to the first prominent peak of its small momentum transfer of the scattered radiation, leading to inaccurate determination of the transport properties. Here, it is proposed to use the rescaled mean spherical approximation under the requirement of fitting the experimental data of the structure beyond the dependence of more significant wave numbers. The predicted viscosity agrees with the observed ones at a low volume fraction of particles for ferrofluids dispersed in polymer solvents. This rheological quantity is inversely related to the self-diffusion coefficient of a tracer particle. Full article
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Article
A Colorimetric Detection of Noradrenaline in Wastewater Using Citrate-Capped Colloidal Gold Nanoparticles Probe
Colloids Interfaces 2022, 6(4), 61; https://doi.org/10.3390/colloids6040061 - 31 Oct 2022
Viewed by 426
Abstract
This study reports a simple, fast, and low-cost detection of noradrenaline (NA) in wastewater using citrate-capped colloidal gold nanoparticles (AuNPs). The addition of NA to citrate-capped colloidal AuNPs generates a colour modulation that the bare eye can detect due to the aggregation of [...] Read more.
This study reports a simple, fast, and low-cost detection of noradrenaline (NA) in wastewater using citrate-capped colloidal gold nanoparticles (AuNPs). The addition of NA to citrate-capped colloidal AuNPs generates a colour modulation that the bare eye can detect due to the aggregation of the colloidal AuNPs. The relationship between the NA concentration and colloidal AuNPs aggregation was further monitored by ultraviolet–visible light (UV–vis) spectroscopy in an aqueous solution. The method displayed a linear range of 0–500 μM with R2 = 0.99 and an LOD and LOQ of 42.2 and 140.5 μM. Application in an environmental sample collected from the Darville Wastewater Treatment Plant shows that this work provided a cost-effective and spectrophotometric method that could be used for monitoring contamination in wastewater. Full article
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Article
Transient Analysis of the Electro-Osmotic Flow of Multilayer Immiscible Maxwell Fluids in an Annular Microchannel
Colloids Interfaces 2022, 6(4), 60; https://doi.org/10.3390/colloids6040060 - 24 Oct 2022
Viewed by 376
Abstract
This work investigates the transient multilayer electro-osmotic flow of viscoelastic fluids through an annular microchannel. The dimensionless mathematical model of multilayer flow is integrated by the linearized Poisson-Boltzmann equation, the Cauchy momentum equation, the rheological Maxwell model, initial conditions, and the electrostatic and [...] Read more.
This work investigates the transient multilayer electro-osmotic flow of viscoelastic fluids through an annular microchannel. The dimensionless mathematical model of multilayer flow is integrated by the linearized Poisson-Boltzmann equation, the Cauchy momentum equation, the rheological Maxwell model, initial conditions, and the electrostatic and hydrodynamic boundary conditions at liquid-liquid and solid-liquid interfaces. Although the main force that drives the movement of fluids is due to electrokinetic effects, a pressure gradient can also be added to the flow. The semi-analytical solution for the electric potential distribution and velocity profiles considers analytical techniques as the Laplace transform method, with numerical procedures using the inverse matrix method for linear algebraic equations and the concentrated matrix exponential method for the inversion of the Laplace transform. The results presented for velocity profiles and velocity tracking at the transient regime reveal an interesting oscillatory behavior that depends on elastic fluid properties via relaxation times. The time required for the flow to reach steady-state is highly dependent on the viscosity ratios and the dimensionless relaxation times. In addition, the influence of other dimensionless parameters on the flow as the electrokinetic parameters, zeta potentials at the walls, permittivity ratios, ratio of pressure forces to electro-osmotic forces, number of fluid layers, and annular thickness are investigated. The findings of this study have significant implications for the precise control of parallel fluid transport in microfluidic devices for flow-focusing applications. Full article
(This article belongs to the Special Issue Rheology of Complex Fluids and Interfaces)
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Article
Deposition of Colloidal Magnetite on Stainless Steel in Simulated Steam Generator Conditions—Experiments and Modeling
Colloids Interfaces 2022, 6(4), 59; https://doi.org/10.3390/colloids6040059 - 21 Oct 2022
Viewed by 315
Abstract
Sludge formation via colloidal magnetite deposition in steam generators is an important phenomenon that significantly influences the thermohydraulic properties and corrosion of structural materials. This paper aims to verify a model of sludge deposition and consolidation with emphasis on its most significant parameters [...] Read more.
Sludge formation via colloidal magnetite deposition in steam generators is an important phenomenon that significantly influences the thermohydraulic properties and corrosion of structural materials. This paper aims to verify a model of sludge deposition and consolidation with emphasis on its most significant parameters and their experimental estimation. In-situ electrochemical impedance spectroscopic (EIS) measurements are employed for quantitative evaluation of magnetite deposition kinetics on stainless steel in ammonia-ethanolamine (AMETA) secondary coolant at different temperatures. Parameterization of the model by quantitative comparison of the mixed-conduction model (MCM) with experimental data is discussed. Model predictions are compared with literature data from laboratory experiments and plant operation. Conclusions are drawn about the applicability of the model for quantitative assessment of sludge deposition and consolidation rates. Full article
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Article
Drop Impact onto a Substrate Wetted by Another Liquid: Flow in the Wall Film
Colloids Interfaces 2022, 6(4), 58; https://doi.org/10.3390/colloids6040058 - 20 Oct 2022
Viewed by 380
Abstract
The impact of a drop onto a liquid film is relevant for many natural phenomena and industrial applications such as spray painting, inkjet printing, agricultural sprays, or spray cooling. In particular, the height of liquid remaining on the substrate after impact is of [...] Read more.
The impact of a drop onto a liquid film is relevant for many natural phenomena and industrial applications such as spray painting, inkjet printing, agricultural sprays, or spray cooling. In particular, the height of liquid remaining on the substrate after impact is of special interest for painting and coating but also for applications involving heat transfer from the wall. While much progress has been made in explaining the hydrodynamics of drop impact onto a liquid film of the same liquid, the physics of drop impact onto a wall film with different material properties is still not well understood. In this study, drop impact onto a very thin liquid film of another liquid is investigated. The thickness of the film remaining on a substrate after drop impact is measured using a chromatic-confocal line sensor. It is interesting that the residual film thickness does not depend on the initial thickness of the wall film, but strongly depends on its viscosity. A theoretical model for the flow in the drop and wall film is developed which accounts for the development of viscous boundary layers in both liquids. The theoretical predictions agree well with the experimental data. Full article
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Article
Bionanocomposite Active Packaging Material Based on Soy Protein Isolate/Persian Gum/Silver Nanoparticles; Fabrication and Characteristics
Colloids Interfaces 2022, 6(4), 57; https://doi.org/10.3390/colloids6040057 - 18 Oct 2022
Viewed by 826
Abstract
In this study, nanocomposite active films were fabricated containing silver nanoparticles (SNPs) embedded within soy protein isolate (SPI)/Persian gum (PG) matrices. The physical, mechanical, and antibacterial properties of these composite films were then characterized. In addition, scanning electron microscopy (SEM), Fourier transform infrared [...] Read more.
In this study, nanocomposite active films were fabricated containing silver nanoparticles (SNPs) embedded within soy protein isolate (SPI)/Persian gum (PG) matrices. The physical, mechanical, and antibacterial properties of these composite films were then characterized. In addition, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) were used to provide information about the microstructure, interactions, and crystallinity of the films. Pure SPI films had poor physicochemical attributes but the addition of PG (0.25, 0.5, or 1 wt%) improved their water vapor permeability, mechanical properties, and water solubility (WS). The moisture content (MC) of the films decreased after the introduction of PG, which was attributed to fewer free hydroxyl groups to bind to the water molecules. Our results suggest there was a strong interaction between the SPI and the PG and SNPs in the films, suggesting these additives behaved like active fillers. Optimum film properties were obtained at 0.25% PG in the SPI films. The addition of PG (0.25%) and SNPs (1%) led to a considerable increase in tensile strength (TS) and a decrease in elongation at break (EB). Furthermore, the incorporation of the SNPs into the SPI/PG composite films increased their antibacterial activity against pathogenic bacteria (Escherichia coli and Staphylococcus aureus), with the effects being more prominent for S. aureus. Spectroscopy analyses provided insights into the nature of the molecular interactions between the different components in the films. Overall, the biodegradable active films developed in this study may be suitable for utilization as eco-friendly packaging materials in the food industry. Full article
(This article belongs to the Special Issue Biocolloids and Biointerfaces)
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Article
Unfolded Lipase at Interfaces Studied via Interfacial Dilational Rheology: The Impact of Urea
Colloids Interfaces 2022, 6(4), 56; https://doi.org/10.3390/colloids6040056 - 17 Oct 2022
Viewed by 411
Abstract
Unfolding can interrupt the activity of enzymes. Lipase, the enzyme responsible for triglyceride catalysis, can be deactivated by unfolding, which can significantly affect the yield of enzymatic processes in biochemical engineering. Different agents can induce lipase unfolding, among which we study the impact [...] Read more.
Unfolding can interrupt the activity of enzymes. Lipase, the enzyme responsible for triglyceride catalysis, can be deactivated by unfolding, which can significantly affect the yield of enzymatic processes in biochemical engineering. Different agents can induce lipase unfolding, among which we study the impact of urea as a strong denaturant. Unfolding weakens the rigidity and stability of globular proteins, thereby changing the viscoelastic properties of the protein adsorbed layers. These changes can be detected and quantified using interfacial dilational rheology. The urea-induced unfolding of lipase destructs its globular structure, making it more flexible. The interfacial tension and viscoelastic moduli of lipase adsorbed layers reduce upon the addition of urea in the range of studied concentrations. The results agree with the theory that, upon unfolding, a distal region of the loop and tail domain forms adjacent to the proximal region of the interface. The exchange of matter between these regions reduces the viscoelasticity of the unfolded lipase adsorbed layers. Additionally, unfolding reduces the rigidity and brittleness of the lipase adsorbed layers: the aged adsorbed layer of native lipase can break upon high-amplitude perturbations of the interfacial area, unlike the case for urea-induced unfolded lipase. Full article
(This article belongs to the Special Issue Biocolloids and Biointerfaces)
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Article
Why Is the Linearized Form of Pseudo-Second Order Adsorption Kinetic Model So Successful in Fitting Batch Adsorption Experimental Data?
Colloids Interfaces 2022, 6(4), 55; https://doi.org/10.3390/colloids6040055 - 12 Oct 2022
Cited by 1 | Viewed by 418
Abstract
There is a vast amount of literature devoted to experimental studies on adsorption from liquids examining the adsorption potential of various adsorbents with respect to various solutes. Most of these studies contain not only equilibrium but also kinetic experimental data. The standard procedure [...] Read more.
There is a vast amount of literature devoted to experimental studies on adsorption from liquids examining the adsorption potential of various adsorbents with respect to various solutes. Most of these studies contain not only equilibrium but also kinetic experimental data. The standard procedure followed in the literature is to fit the kinetic experimental adsorption data to some models. Typically empirical models are employed for this purpose and among them, the pseudo-first and pseudo-second order kinetic models are the most extensively used. In particular, the linear form of their integrated equations is extensively employed. In most cases, it is found that the pseudo-second order model is not only better than other models but also leads to high fitting quality. This is rather strange since there is no physical justification for such a model, as it is well accepted that adsorption kinetics is dominated by a diffusion process. In the present work, it will be shown through examples and discussion that the success of the linearized pseudo-second order model in fitting the data is misleading. Specific suggestions on appropriate adsorption data treatment are given. Full article
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Article
A Molecular View of the Surface Pressure/Area Per Lipid Isotherms Assessed by FTIR/ATR Spectroscopy
Colloids Interfaces 2022, 6(4), 54; https://doi.org/10.3390/colloids6040054 - 11 Oct 2022
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Abstract
The macroscopic behavior of a lipid monolayer in terms of packing and compressibility properties is classically obtained from surface pressure/area per molecule isotherms. Molecular interpretations trying to fit the II/A curves have been attempted by molecular dynamics. In this regard, the simulation is [...] Read more.
The macroscopic behavior of a lipid monolayer in terms of packing and compressibility properties is classically obtained from surface pressure/area per molecule isotherms. Molecular interpretations trying to fit the II/A curves have been attempted by molecular dynamics. In this regard, the simulation is performed by introducing parameters accounting for the lipid-lipid interaction in the monolayer plane. However, water, as an essential component of the interfacial phenomena, is not explicitly included in terms of molecular arrays. This drawback appears to be a consequence of the lack of experimental evidence that may complement the macroscopic view with the microscopic features. In this work, we propose that II/A curves can be reproduced from microscopic molecular data obtained with FTIR/ATR spectroscopy. The changes in surface pressure, in fact, changes in the surface tension of the lipid–water interphase, can be related to the acyl regions exposed to water and evaluated by the ratio of isolated-to-connected CH2 populations. In turn, the area changes correspond to the variations in the primary and secondary hydration shells of the phosphate region. The isolated/connected CH2 ratio represents the extension of the non-polar region exposed to water and is linked to the resulting water surface tension. The area per lipid is determined by the excluded volume of the hydration shells around the phosphate groups in correlation to the carbonyl groups. The derivative of the frequencies of the -CH2 groups with respect to the water content gives an insight into the influence of water arrangements on the compressibility properties, which is important in understanding biologically relevant phenomena, such as osmotic stress in cells and the mechanical response of monolayers. It is concluded that the water population distributed around the different groups dominates, to a great extent, the physical properties of the lipid membranes. Full article
(This article belongs to the Special Issue Biocolloids and Biointerfaces)
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Review
Marangoni Patterns in a Non-Isothermal Liquid with Deformable Interface Covered by Insoluble Surfactant
Colloids Interfaces 2022, 6(4), 53; https://doi.org/10.3390/colloids6040053 - 29 Sep 2022
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Abstract
Marangoni patterns are created by instabilities caused by thermocapillary and solutocapillary stresses on the deformable free surface of a thin liquid layer. In the present paper, we consider the influence of the insoluble surfactant on the selection and modulational instability of stationary Marangoni [...] Read more.
Marangoni patterns are created by instabilities caused by thermocapillary and solutocapillary stresses on the deformable free surface of a thin liquid layer. In the present paper, we consider the influence of the insoluble surfactant on the selection and modulational instability of stationary Marangoni patterns near their onset threshold. The basic governing parameters of the problem are the Biot number characterizing the heat-transfer resistances of and at the surface, the Galileo number indicating the role of gravity via viscous forces, and the elasticity number specifying the influence of insoluble surfactant on the interfacial dynamics of the liquid. The paper includes a review of the previous results obtained in that problem as well as new ones. Full article
(This article belongs to the Special Issue Feature Reviews in Colloids, Nanomaterials, and Interfaces)
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Article
Structural Modification of Jackfruit Leaf Protein Concentrate by Enzymatic Hydrolysis and Their Effect on the Emulsifier Properties
Colloids Interfaces 2022, 6(4), 52; https://doi.org/10.3390/colloids6040052 - 28 Sep 2022
Viewed by 600
Abstract
Jackfruit leaf protein concentrate (LPC) was hydrolyzed by pepsin (H–Pep) and pancreatin (H–Pan) at different hydrolysis times (30–240 min). The effect of the enzyme type and hydrolysis time of the LPC on the amino acid composition, structure, and thermal properties and its relationship [...] Read more.
Jackfruit leaf protein concentrate (LPC) was hydrolyzed by pepsin (H–Pep) and pancreatin (H–Pan) at different hydrolysis times (30–240 min). The effect of the enzyme type and hydrolysis time of the LPC on the amino acid composition, structure, and thermal properties and its relationship with the formation of O/W emulsions were investigated. The highest release of amino acids (AA) occurred at 240 min for both enzymes. H–Pan showed the greatest content of essential and hydrophobic amino acids. Low β-sheet fractions and high β-turn contents had a greater influence on the emulsifier properties. In H–Pep, the β-sheet fraction increased, while in H–Pan it decreased as a function of hydrolysis time. The temperatures of glass transition and decomposition were highest in H–Pep due to the high content of β-sheets. The stabilized emulsions with H–Pan (180 min of hydrolysis) showed homogeneous distributions and smaller particle sizes. The changes in the secondary structure and AA composition of the protein hydrolysates by the effect of enzyme type and hydrolysis time influenced the emulsifying properties. However, further research is needed to explore the use of H–Pan as an alternative to conventional emulsifiers or ingredients in functional foods. Full article
(This article belongs to the Special Issue Recent Advances in Emulsions and Applications)
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Article
Isolation and Structural Characterization of Alginates from the Kelp Species Laminaria ochroleuca and Saccorhiza polyschides from the Atlantic Coast of Morocco
Colloids Interfaces 2022, 6(4), 51; https://doi.org/10.3390/colloids6040051 - 27 Sep 2022
Viewed by 494
Abstract
Alginates are linear unbranched polysaccharides produced by brown seaweeds. The gel properties of this phycocolloid are mainly linked to the monomer composition, sequential structure and molecular weight of the polymeric chain. Nevertheless, these structural parameters are also dependent on the age and tissue [...] Read more.
Alginates are linear unbranched polysaccharides produced by brown seaweeds. The gel properties of this phycocolloid are mainly linked to the monomer composition, sequential structure and molecular weight of the polymeric chain. Nevertheless, these structural parameters are also dependent on the age and tissue of the thalli used. In this work, the kelp species Laminaria ochroleuca and Saccorhiza polyschides harvested from the Moroccan coast were analyzed for their alginates content and composition in different thalli parts (blade and stipe). Spectroscopic characterization (1H NMR and FT-IR), viscosity, and molecular weight of the extracted alginates were investigated. The obtained results showed that the alginate contents ranged from 20.19 ± 2 to 49.8 ± 2.4% dw. FT-IR spectroscopy exhibited similar spectra between the alginates extracted from both species and the commercial alginate. The 1H-NMR results revealed interesting variations in block composition between species, and less disparity with regard to the tissue type (M/G values ranging from 0.89 to 2.14). High mannuronate content was found in all alginates except for those extracted from the blade of L. ochroleuca. The homopolymeric fractions FMM are remarkably high compared to the FGG and heteropolymeric fractions (FGM/FMG) in S. polyschides. However, for L. ochroleuca, the heteropolymeric fractions are quite abundant, accounting for more than 34% of the polymer diads. The alginates extracted from both species indicated low values for the intrinsic viscosity. Based on the yield and the structural properties of their alginates, this study suggests that both L. ochroleuca and S.polyschides could be considered potential alginophytes to be incorporated into the industry of alginates. It also proposes an optimization of the yield, using the different thalli parts in the extraction (blade and stipe). The chemical structure and viscosity of their alginates may contribute to expanding their applications, especially in biotechnology and medical fields. Full article
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Article
Ultrasound-Assisted Extraction of Artocarpus heterophyllus L. Leaf Protein Concentrate: Solubility, Foaming, Emulsifying, and Antioxidant Properties of Protein Hydrolysates
Colloids Interfaces 2022, 6(4), 50; https://doi.org/10.3390/colloids6040050 - 26 Sep 2022
Viewed by 529
Abstract
The impact of ultrasound-assisted extraction (UAE) was evaluated on the functionality of jackfruit leaf protein hydrolysates. Leaf protein concentrate was obtained by ultrasound (LPCU) and conventional extractions by maceration (LPCM). LPCM and LPCU were hydrolyzed with pancreatin (180 min), and hydrolysates by maceration [...] Read more.
The impact of ultrasound-assisted extraction (UAE) was evaluated on the functionality of jackfruit leaf protein hydrolysates. Leaf protein concentrate was obtained by ultrasound (LPCU) and conventional extractions by maceration (LPCM). LPCM and LPCU were hydrolyzed with pancreatin (180 min), and hydrolysates by maceration (HM) and ultrasound (HU) were obtained. The composition of amino acids, techno-functional (solubility, foaming, and emulsifying properties), and antioxidant properties of the hydrolysates were evaluated. A higher amount of essential amino acids was found in HU, while HM showed a higher content of hydrophobic amino acids. LPCs exhibited low solubility (0.97–2.89%). However, HM (67.8 ± 0.98) and HU (77.39 ± 0.43) reached maximum solubility at pH 6.0. The foaming and emulsifying properties of the hydrolysates were improved when LPC was obtained by UAE. The IC50 of LPCs could not be quantified. However, HU (0.29 ± 0.01 mg/mL) showed lower IC50 than HM (0.32 ± 0.01 mg/mL). The results reflect that the extraction method had a significant (p < 0.05) effect on the functionality of protein hydrolysates. The UAE is a suitable method for enhancing of quality, techno-functionality, and antioxidant properties of LPC. Full article
(This article belongs to the Special Issue Recent Advances in Emulsions and Applications)
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