Colloids Interfaces, Volume 7, Issue 4 (December 2023) – 11 articles

The wettability of quartz by different liquids and solutions plays a very important role in practical applications. Hence, the wetting behaviour of ethanol (ET), rhamnolipid (RL) and Triton X-165 (TX165) aqueous solutions with regard to the quartz surface tension was investigated. The investigations were based on the contact angle measurements of water (W), formamide (F) and diiodomethane (D) as well as ET, RL and TX165 solutions on the quartz surface. The obtained results of the contact angle for W, F and D were used for the determination of quartz surface tension as well as its components and parameters using different approaches, whereas the results obtained for the aqueous solution of ET, RL and TX165 were considered with regard to their adsorption at the quartz–air, quartz–solution and solution–air interfaces as well as the solution interactions across the quartz–solution interface. The considerations of the relations between the contact angle and adsorption of solution components at different interfaces were based on the components and parameters of the quartz surface tension. They allow us to, among other things, establish the mechanism of the adsorption of individual components of the solution at the interfaces and standard Gibbs surface free energy of this adsorption. Full article

The calcium ions (Ca²⁺) of calcium hydroxyapatite (CaHap) were substituted with zinc ions (Zn²⁺), and zinc–calcium hydroxyapatite solid solution (ZnCaHap) particles were prepared via a precipitation method. The structure of the various obtained particles was investigated via powder X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectrometry. The ultraviolet (UV) absorption ability of the particles was also investigated using UV–Vis spectroscopy. The morphology of the CaHap comprised fine ellipsoidal particles, and long rod-like particles and large plate-like particles were mixed with the fine particles at higher Zn²⁺ contents in the particles. Pure ZnCaHap particles were obtained from the starting solution at less than Zn/(Zn + Ca) ([X_Zn]) of 0.25. Another crystal phase was mixed with the ZnCaHap phase at [X_Zn] ≥ 0.25. The crystallinity and lattice parameters a and c of the particles decreased with an increase in [X_Zn] from 0 to 0.10. The UV absorptive ability of the particles first increased and then decreased with increasing Zn²⁺ content and showed a maximum at [X_Zn] = 0.30. Full article

We study the interaction between a flat surface and a contaminant solution. The surface is protected by a grafted polymer layer. Our primary interest is to better understand and elucidate the effect of simple molecular interactions on the contamination and decontamination of the surface through molecular diffusion. These interactions manifest themselves in the potential of mean force that the contaminant molecule experiences as it diffuses across the grafted polymer layer. For simplicity, we consider that all interactions are of the hard-sphere type. The size of the contaminant molecule is the same as that of the solvent as well as the individual polymer segment. Despite these simplifications, the analysis offers important physical insights and a qualitative description of the contamination and decontamination processes. Full article

Emulsions containing crystalline dispersed phases hold significant importance in pharmaceutical, chemical, and life science industries. The industrial agitation and storage of these emulsions can prompt crystallization effects within the flow field, intersecting with the primary nucleation mechanisms. Notably, contact-mediated nucleation, in which subcooled droplets crystallize upon contact with a crystalline particle, and shear-induced crystallization due to droplet deformation, are both conceivable phenomena. This study delves into the crystallization processes of emulsions in a 1 L stirred vessel, integrating an ultrasonic probe to monitor droplet crystallization progression. By scrutinizing the influence of the flow field and of the emulsifiers stabilizing the droplets, our investigation unveils the direct impact of enhanced rotational speed on accelerating the crystallization rate, correlating with increased energy input. Furthermore, the concentration of emulsifiers is observed to positively affect the crystallization process. Significantly, this pioneering investigation marks the first evaluation of emulsion crystallization considering the overlapping nucleation mechanisms seen in industrial production of melt emulsions. The findings offer valuable insights for more systematic control strategies in emulsion crystallization processes, promising more efficient and sustainable industrial practices by enabling targeted application of shear and surfactants. Full article

The light-based nanowelding of metallic nanoparticles is of particular interest because it provides convenient and controlled means for the conversion of nanoparticles into microstructures and the fabrication of nanodevices. In this study, we investigated the wavelength dependence of laser-induced nanowelded shapes of silver nanoparticles (AgNPs). We observed that the nanowelded microstructures illuminated with only a 405 nm laser were more branched than those formed via illumination using both the 405 nm and 532 nm lasers. We quantified this observation by two compactness descriptors and examined the dependence of the power of the 532 nm laser. More importantly, to understand the experimental observations, we formulated and tested a hypothesis by calculating the wavelength-dependent electric field enhancement due to the surface plasmon resonance of the AgNPs and nanowelded microstructures when illuminated with lights at the two wavelengths. Based on the different patterns of hot spots for welding AgNPs from these calculations, numerical simulations successfully reproduced the different shapes of nanowelded microstructures, supporting our hypothesis. This work suggests the possibility of light-based control of the shapes of laser-induced nanowelded microstructures of metallic nanoparticles. This work is expected to facilitate the development of broader applications using the nanowelding of metallic nanoparticles. Full article

This study focuses on the synthesis of silver nanoparticles (AgNPs) at different high concentrations and investigates their physicochemical properties, antimicrobial activity, and cytotoxicity. AgNPs were synthesized using the alcohol reduction process, involving the reduction of AgNO₃ and its subsequent stabilization via PVP at 80 °C for 4 h. The AgNO₃/PVP molar ratio and the average molecular weight were modified in this study. Characterization analyses revealed that the synthesized AgNPs exhibited characteristic surface plasmon resonance absorption peaks at approximately 415 nm, as observed in the UV–Vis spectrum. The results presented in X-ray diffractograms confirmed the face-centered cubic structure of metallic Ag in the nanoparticles. The nanoparticles demonstrated uniform size and shape, with controllable dimensions ranging from 3 to 800 nm. Regarding antimicrobial activity, the MIC solutions exhibited higher potency against the planktonic cells of Candida albicans. The determination of inhibition halos indicated that the silver nanoparticles had an impact on the microorganisms Streptococcus mutans, Candida albicans, and Actinomyces israelii. Furthermore, lower-concentration compositions showed reduced cytotoxic effects compared to higher-concentration particles. Based on the findings, it was concluded that the AgNO₃/PVP molar ratio plays a crucial role in the production of AgNPs. These synthesized nanoparticles exhibit desirable physicochemical properties and demonstrate potential antimicrobial activity and controlled cytotoxicity. Full article

Plant-based seafood analogs are gaining increasing popularity as replacements for traditional fish and other seafood products due to environmental (stock depletion, pollution, and bycatch issues) and health (bioaccumulated toxins, norovirus, and allergies) concerns associated with them. Several companies have launched plant-based fish products, but the market still lacks alternatives to shellfish and other sea delicacies. In this study, a plant-based sea foie gras (monkfish liver product) analog was developed using duckweed RuBisCO protein and omega-3-rich flaxseed oil to form emulsion gels. These gels consisted of a high concentration of flaxseed oil droplets dispersed within a gelled RuBisCO protein network. It was hypothesized that the high disperse phase volume fraction of the oil droplets and the heat-set gelation properties of the RuBisCO proteins would enable us to create emulsion gels that mimicked the properties of sea foie gras. A natural pigment (β-carotene) was incorporated into the oil phase of the emulsions to mimic the red-orange color of conventional sea foie gras. The structural, textural, and optical properties of real and plant-based sea foie gras analogs were characterized using scanning electron microscopy, confocal microscopy, dynamic shear rheology, texture profile analysis, and colorimetry. Emulsion gels prepared using 40% flaxseed oil and 10% RuBisCO proteins produced plant-based products that closely simulated the texture and color of the real products. Rheological analysis suggested that the oil droplets acted as active fillers within the protein gels. Our results suggest that emulsion gels may be used to create more sustainable and healthier plant-based seafood products. Full article

Clove essential oil is traditionally used as an anesthetic, analgesic, or insecticide, and recently, its applications as an antimicrobial, antioxidant, or anticancer agent have been explored. Nanoemulsions are thermodynamically unstable dispersions (d < 100 nm) produced by mixing two immiscible phases, which, in many cases, improve the stability and biological activities of functional ingredients for pharmaceutical, cosmetic, or food applications. This research optimized the formation of clove essential oil nanoemulsions by employing response surface methodology. The surfactant concentration was minimized by modifying the percentage of clove oil (0–100%), surfactant content (1–4%), and oil phase content (0–20%). In the optimum conditions, a nanoemulsion (93.19 ± 3.92 nm) was produced using 1.0% surfactant and 2.5% oil phase of which 50.7% was clove essential oil. The optimized nanoemulsion was stable in rapid stability tests (centrifugation, freezing–thawing, and heating–cooling), but its average droplet size increased during storage at different temperatures. The nanoemulsion contains a phenolic content equivalent to 736 mg gallic acid/mL. However, the antioxidant capacity of the essential oil (IC₅₀ = 0.78 µg/mL) was dismissed in the nanoemulsion (IC₅₀ = 2.43 µg/mL). The antimicrobial activity of the nanoemulsion showed strain–dependent behavior with MIC ranging from 0.0468 to 0.75 mg/mL, where E. coli and S. typhimurium were the most susceptible pathogenic bacteria. Finally, nanoencapsulation of clove oil showed higher in vitro cytotoxic activity against Caco–2 cancer cells (227 μg/mL) than free clove essential oil (283 μg/mL), but nanoemulsion (306 μg/mL) was less effective than oil (231 μg/mL) in the HT–29 line. This research shows the potential of clove essential oil nanoemulsions for developing biological therapies to treat diseases. Full article

The flow field around a straight chain of multiple slip spherical particles rotating steadily in an incompressible Newtonian fluid about their line of centers is analyzed at low Reynolds numbers. The particles may vary in radius, slip coefficient, and angular velocity, and they are permitted to be unevenly spaced. Through the use of a boundary collocation method, the Stokes equation governing the fluid flow is solved semi-analytically. The interaction effects among the particles are found to be noteworthy under appropriate conditions. For the rotation of two spheres, our collocation results for their hydrodynamic torques are in good agreement with the analytical asymptotic solution in the literature obtained by using a method of twin multipole expansions. For the rotation of three spheres, the particle interaction effect indicates that the existence of the third particle can influence the torques exerted on the other two particles noticeably. The interaction effect is stronger on the smaller or less slippery particles than on the larger or more slippery ones. Torque results for the rotation of chains of many particles visibly show the shielding effect among the particles. Full article

Specific self-assembly is registered in aqueous solution formulations based on four-antennary oligoglycines (T4), namely a spontaneous onset of highly ordered nanostructures—tectomers. This phenomenon is initiated by the action of hydrogen-bonding interactions that promote molecular recognition propensities involving Polyglycine-II-type non-canonical architecture. The result is the formation of positively charged supramolecular entities. These have high potential to capture bacterial endotoxins, like lipopolysaccharides (LPSs). By now, it has been established that the overall properties of these systems can be precisely regulated and gradually changed through fine-tuning the parameters in the aqueous environment (composition, pH, etc.). One unexplored option is to clarify the impact of temperature variations. The aim of the present study is to implement systematic investigations on how changes in temperature influence the various options for the removal of trace LPS quantities, captured by the T4 tectomers. The additional goal is to verify the possibility to develop consecutive paths of recovering the extra T4 quantities that have not participated in the formation of T4+LPS complexes. Some prospects for further applications, e.g., in medicine and pharmaceutics, are also generally outlined. Full article

Silicate mineral powders (SMP) from weathered granite soil from Kazakhstan are proposed for the desalination of potash brines containing sodium, potassium and chloride ions. Batch adsorption experiments using acid-treated silicate (AS) achieved a Na⁺/K⁺/Cl⁻ recovery of ~13/28/6 mg/g. An isothermal study best fitted the Freundlich and Dubinin–Radushkevich models for Na⁺ and K⁺/Cl⁻. The kinetic data were best modeled by pseudo-second-order kinetics for Na⁺/K⁺ and pseudo-first-order for Cl⁻. Thermodynamic calculations showed spontaneity under natural conditions. For Na⁺/K⁺, physisorption is accompanied by ion exchange. To study the possibility of sorbent reuse, several cycles of K⁺/Na⁺ adsorption–desorption were carried out under optimal conditions. AS selectively adsorbed potassium ions, maintaining a high effectiveness during five cycles providing K-form silicate fertilizers. Leachates of spent AS contain high concentrations of K/Na/Ca/Mg and other microelements essential for plants. Thus, SMP resolve two issues: the desalination of brine and the provision of fertilizer. Full article