Search Results (33)

This work studies the stabilization of Pickering-like emulsions using dispersions of interpolyelectrolyte complexes (IPECs) formed by chitosan (CS) and sodium alginate (ALG), two polymers from natural resources, as the aqueous phase and soybean oil as the oil phase. The ability of these bio-based IPECs to form stable emulsions was evaluated by varying the compositional ratio of CS to ALG (Z-ratio) and the oil volume fraction (ϕ_o). Turbidity, zeta potential, and dynamic light scattering measurements revealed the dependence of IPEC properties on the Z-ratio, with phase separation observed near stoichiometric ratios. Phase diagram analysis showed that stable oil-in-water (O/W) and water-in-oil (W/O) emulsions could be obtained under certain combinations of the Z-ratio and ϕ_o. Emulsion stability increased with higher Z-ratios due to increased interfacial activity of the complexes and reduced coalescence. Emulsions with high ϕ_o exhibited transitions from discrete droplets to bicontinuous interfacially jammed emulsion gels (bijels), suggesting tunable morphologies. These results highlight the potential of CHI-ALG IPECs as eco-friendly and efficient stabilizers of Pickering-like emulsions for applications in food, cosmetics and pharmaceuticals. Full article

This study examines the adsorption and bulk assembly behaviour of quaternized hydroxyethylcellulose ethoxylate (QHECE)–sodium dodecyl sulphate (SDS) complexes on negatively charged substrates. Due to its quaternized structure, QHECE, which is used in several industries, including cosmetics, exhibits enhanced electrostatic interactions. The phase behaviour and adsorption mechanisms of QHECE–SDS complexes are investigated using model substrates that mimic the wettability and surface charge of damaged hair fibres. Two preparation methodologies, high-concentration mixing and gradient-free mixing, were employed to examine their impact on the complex equilibrium, phase behaviour, and adsorption properties of the complexes. The measurements of turbidity, electrophoretic mobility, and conductivity demonstrate the existence of nonequilibrium dynamics during the mixing process, which exert a significant influence on the structural and functional characteristics of the complexes. The quartz crystal microbalance with dissipation monitoring (QCM-D) was employed to investigate the adsorption of the complexes onto the substrates. The results demonstrated the critical role of intermediate SDS concentrations in enhancing deposition. The findings emphasise the importance of formulation and preparation protocols in designing stable, high-performance cosmetic products. This research advances our understanding of polyelectrolyte–surfactant interactions and provides insights into optimising QHECE-based formulations. Full article

This work investigated the gelation kinetics and mechanical properties of agarose hydrogels studied at different concentrations (in the range 1–5 g/L) and temperatures. Rheological measurements were performed by diffusing wave spectroscopy (DWS) using polystyrene and titanium dioxide particles as probes. The study emphasized the influence of gelation kinetics on the mechanical behavior of the hydrogels. The results showed that the gel properties were closely related to the thermal history and aging time of the samples. The insights gained from this study are critical for optimizing the performance of agarose hydrogels in specific applications and highlight the importance of controlling the concentration and thermal conditions during hydrogel preparation. Full article

This study examines the potential of fungal chitosan derived from Aspergillus niger as a sustainable alternative to traditional petrochemical-based ingredients in cosmetic products. Specifically, the research examines the solubility of fungal chitosan in aqueous solutions of varying ionic strength and its adsorption onto negatively charged surfaces that mimic human hair keratin. The adsorption behavior, water content, and frictional properties of chitosan films were evaluated using a quartz crystal microbalance with dissipation monitoring and a surface force apparatus (SFA). The findings indicated that fungal chitosan exhibits good solubility at a pH of 4.5. Conversely, the adsorption of chitosan is subject to the influence of both polymer concentration and ionic strength. At the lowest ionic strengths, a screening-enhanced adsorption process occurs as a consequence of the reduction in chitosan solubility in the presence of salt. This results in the depletion of polymer chains from the solution and their subsequent deposition. An increase in ionic strength above 15–20 mM results in a worsening of the chitosan–surface interaction, due to the simultaneous screening of both the chitosan and the surface charges. This results in a hindrance to the adsorption process. The deposited films are highly hydrated, and this hydration increases with both polymer concentration and ionic strength. Furthermore, the films exhibit a predominantly elastic behavior, and the response of the films under shear deformations shows a strong dependence on the polymer concentration. These findings contribute to the development of environmentally friendly cosmetic formulations that meet consumer demands for sustainability. Full article

Agave tequilana Weber var. Blue is used as the primary raw material in tequila production due to its fructans (inulin) content. This study evaluates the formulation of a plant-growth-promoting bacteria (PGPB) consortium (Pseudomonas sp. and Shimwellia sp.) to increase sugars in A. tequilana under field conditions. A total of three doses were tested: low (5 L ha⁻¹), medium (10 L ha⁻¹), and high (15 L ha⁻¹), with a cellular density of 1 × 10⁸ CFU mL⁻¹ and one control treatment (without application). Total reducing sugars (TRS), inulin, sucrose, glucose, fructose, and plant growth were measured in agave plants aged 4–5 years at 0 (T0), 3 (T3), 6 (T6), and 12 (T12) months. Yield was recorded at T12. The TRS increased by 3%, and inulin by 5.3% in the high-dose treatment compared to the control at T12. Additionally, a low content of sucrose, glucose, and fructose (approximately 1%) was detected. At T12, the weight of agave heads increased by 31.2% in the medium dose and 22.3% in the high dose compared to the control. The high dose provided a higher inulin content. The A. tequilana plants were five years old and exhibited growth comparable to the standards for 6–7-year-old plants. This study demonstrates a sustainable strategy for tequila production, optimizing the use of natural resources and enhancing industry performance through increased sugar content and yield. Full article

This study investigates the effect of an inert salt (NaCl) on the equilibrium interfacial tension and dilatational modulus of Pluronic F-68 copolymer, a triblock copolymer consisting of two terminal blocks of poly(ethylene oxide) and a less hydrophilic central block of poly(propylene oxide). Interfacial tension measurements were carried out using a surface force balance and a drop shape tensiometer, while rheological measurements were carried out in two different frequency ranges. This involved the use of the oscillatory barrier/droplet method and electrocapillary wave measurements, complemented by an appropriate theoretical framework. This work aimed to elucidate the influence of NaCl on the interfacial behavior of Gibbs monolayers of Pluronic F-68. In addition, this study highlights some of the technical and theoretical limitations associated with obtaining reliable dilatational rheological data at high frequencies (<1 kHz) using electrocapillary wave measurements. The results provide valuable insights into the interplay between salt presence and interfacial properties of Pluronic F-68 and highlight the challenges of obtaining accurate dilatational rheological data under specific measurement conditions. Full article

This study investigates the surface modification of hydrophilic silica nanoparticles by non-chemical adsorption of an amphiphilic triblock copolymer, Pluronic F-127, and elucidates its influence on the interfacial dispersion properties. The interaction between Pluronic F-127 and silica nanoparticles drives the formation of copolymer-decorated particles with increased hydrodynamic diameter and reduced effective charge as the copolymer concentration increases, while the opposite effect occurs as the particle concentration increases at a fixed polymer concentration. This indicates that increasing the copolymer concentration leads to an increase in the coating density, whereas increasing the particle concentration leads to a decrease. This is of paramount importance for modulating the reorganization of the Pluronic F-127 shell upon adsorption at fluid–fluid interfaces and, thus, the adsorption of the decorated nanoparticles at the interface and the rheological properties of the obtained layers. In fact, the relationship between copolymer concentration and interfacial tension, as well as the mechanical response of the interface, mirrors the patterns observed in Pluronic F-127 solutions, and only a shift mediated by the Pluronic F-127 concentration is found. This suggests that the presence of particles limits the space available for Pluronic F-127 molecules to reorganize at the interface but does not significantly affect the interfacial behavior of the particle-laden interface. Full article

This work investigates the effect of dilution on the phase separation process of binary charged polysaccharide–surfactant mixtures formed by two cationic polysaccharides and up to four surfactants of different nature (anionic, zwitterionic, and neutral), as well as the potential impact of dilution-induced phase separation on the formation of conditioning deposits on charged surfaces, mimicking the negative charge and wettability of damaged hair fibers. The results obtained showed that the dilution behavior of model washing formulations (concentrated polysaccharide–surfactant mixtures) cannot be described in terms of a classical complex precipitation framework, as phase separation phenomena occur even when the aggregates are far from the equilibrium phase separation composition. Therefore, dilution-enhanced deposition cannot be predicted in terms of the worsening of colloidal stability due to the charge neutralization phenomena, as common phase separation and, hence, enhanced deposition occurs even for highly charged complexes. Full article

In recent years, the availability of effective vaccines has become a public health challenge due to the proliferation of different pandemic outbreaks which are a risk for the world population health. Therefore, the manufacturing of new formulations providing a robust immune response against specific diseases is of paramount importance. This can be partially faced by introducing vaccination systems based on nanostructured materials, and in particular, nanoassemblies obtained by the Layer-by-Layer (LbL) method. This has emerged, in recent years, as a very promising alternative for the design and optimization of effective vaccination platforms. In particular, the versatility and modularity of the LbL method provide very powerful tools for fabricating functional materials, opening new avenues on the design of different biomedical tools, including very specific vaccination platforms. Moreover, the possibility to control the shape, size, and chemical composition of the supramolecular nanoassemblies obtained by the LbL method offers new opportunities for manufacturing materials which can be administered following specific routes and present very specific targeting. Thus, it will be possible to increase the patient convenience and the efficacy of the vaccination programs. This review presents a general overview on the state of the art of the fabrication of vaccination platforms based on LbL materials, trying to highlight some important advantages offered by these systems. Full article

The concentration dependence of the surface tension of several binary mixtures of non-electrolytes has been measured at 298.15 K. The mixtures have been chosen since they presented a so-called “W-shape” concentration dependence of the excess constant pressure heat capacity and high values of the concentration-concentration correlation function. This behavior was interpreted in terms of the existence of anomalously high concentration fluctuations that resemble those existing in the proximities of critical points. However, no liquid-liquid phase separation has been found in any of these mixtures over a wide temperature range. In this work, we have extended these studies to the liquid-air interfacial properties. The results show that the concentration dependence of the surface tension shows a plateau and the mixing surface tension presents a “W-shape” behavior. To the best of our knowledge, this is the first time that this behavior is reported. The weak anomalies of the surface tension near a liquid-liquid critical point suggest that the results obtained cannot be considered far-from-critical effects. The usual approach of substituting the activity by the concentration in the Gibbs equation for the relative surface concentration has been found to lead to large errors and the mixtures to have a fuzzy and thick liquid/vapor interface. Full article

Fluid/fluid interfaces are ubiquitous in science and technology, and hence, the understanding of their properties presents a paramount importance for developing a broad range of soft interface dominated materials, but also for the elucidation of different problems with biological and medical relevance. However, the highly dynamic character of fluid/fluid interfaces makes shedding light on fundamental features guiding the performance of the interfaces very complicated. Therefore, the study of fluid/fluid interfaces cannot be limited to an equilibrium perspective, as there exists an undeniable necessity to face the study of the deformation and flow of these systems under the application of mechanical stresses, i.e., their interfacial rheology. This is a multidisciplinary challenge that has been evolving fast in recent years, and there is currently available a broad range of experimental and theoretical methodologies providing accurate information of the response of fluid/fluid interfaces under the application of mechanical stresses, mainly dilational and shear. This review focused on providing an updated perspective on the study of the response of fluid/fluid interfaces to dilational stresses; to open up new avenues that enable the exploitation of interfacial dilational rheology and to shed light on different problems in the interest of science and technology. Full article

The cosmetic industry has an undeniable need to design and develop new ecosustainable products to respond to the demands of consumers and international regulations. This requires substituting some traditional ingredients derived from petrochemical sources with new ones with more ecofriendly profiles. However, this transition towards the use of green ingredients in the cosmetic industry cannot compromise the effectiveness of the obtained products. Emerging ingredients in this new direction of the cosmetic industry are chitosan and its derivatives, which combine many interesting physicochemical and biological properties for the fabrication of cosmetic products. Thus, the use of chitosan opens a promising future path to the design of cosmetic formulations. In particular, chitosan’s ability for interacting electrostatically with negatively charged substrates (e.g., skin or damaged hair), resulting in the formation of polymeric films which contribute to the conditioning and moisturizing of cosmetic substrates, makes this polymer an excellent candidate for the design of skin and hair care formulations. This review tries to provide an updated perspective on the potential interest of chitosan and its derivatives as ingredients of cosmetics for skin and hair care. Full article

The manufacturing of stable emulsion is a very important challenge for the cosmetic industry, which has motivated intense research activity for replacing conventional molecular stabilizers with colloidal particles. These allow minimizing the hazards and risks associated with the use of conventional molecular stabilizers, providing enhanced stability to the obtained dispersions. Therefore, particle-stabilized emulsions (Pickering emulsions) present many advantages with respect to conventional ones, and hence, their commercialization may open new avenues for cosmetic formulators. This makes further efforts to optimize the fabrication procedures of Pickering emulsions, as well as the development of their applicability in the fabrication of different cosmetic formulations, necessary. This review tries to provide an updated perspective that can help the cosmetic industry in the exploitation of Pickering emulsions as a tool for designing new cosmetic products, especially creams for topical applications. Full article

The construction of nanostructured materials for their application in electrochemical processes, e.g., energy storage and conversion, or sensing, has undergone a spectacular development over the last decades as a consequence of their unique properties in comparison to those of their bulk counterparts, e.g., large surface area and facilitated charge/mass transport pathways. This has driven strong research on the optimization of nanostructured materials for the fabrication of electrochemical devices, which demands techniques allowing the assembly of hybrid materials with well-controlled structures and properties. The Layer-by-Layer (LbL) method is well suited for fulfilling the requirements associated with the fabrication of devices for electrochemical applications, enabling the fabrication of nanomaterials with tunable properties that can be exploited as candidates for their application in fuel cells, batteries, electrochromic devices, solar cells, and sensors. This review provides an updated discussion of some of the most recent advances on the application of the LbL method for the fabrication of nanomaterials that can be exploited in the design of novel electrochemical devices. Full article

Pickering emulsions stabilized by the interaction of palmitic acid (PA) and silica nanoparticles (SiNPs) at the water/oil interface have been studied using different alkane oil phases. The interaction of palmitic acid and SiNPs has a strong synergistic character in relation to the emulsion stabilization, leading to an enhanced emulsion stability in relation to that stabilized only by the fatty acid. This results from the formation of fatty acid-nanoparticle complexes driven by hydrogen bond interactions, which favor particle attachment at the fluid interface, creating a rigid armor that minimizes droplet coalescence. The comparison of emulsions obtained using different alkanes as the oil phase has shown that the hydrophobic mismatch between the length of the alkane chain and the C16 hydrophobic chain of PA determines the nature of the emulsions, with the solubility of the fatty acid in the oil phase being a very important driving force governing the appearance of phase inversion. Full article