Understanding the role of hydrogen bonding in the aggregation of fumed silica particles in triglyceride solvents

Interfacial Cooperative Assembly of Surfactants and Opposite Wettability Nanoparticles Stabilizes Water-in-Oil Emulsions at High Temperature

Pickering emulsions have promising applications in the development of unconventional oil and gas resources. However, the high-temperature environment of the reservoir is not conducive to the stabilization of Pickering emulsions. In addition, the preparation of Pickering emulsions under low-energy emulsification and low-concentration emulsifier conditions is a difficult challenge. Here, we report a high-temperature resistant water-in-paraffin oil Pickering emulsion, which is synergistically stabilized by polyglycerol ester (PGE) and nanoparticles with opposite wettability (lipophilic silica and hydrophilic alumina). This emulsion can be prepared under mild stirring (500 rpm) conditions and can be stable at 140 °C for at least 30 days. The synergistic effects of surfactant, silicon nanoparticles (MSNPs) with different wettability, and alumina nanoparticles (AONPs) on the stability of both emulsions and water-oil interfacial membranes were investigated through bottle experiments, cryogenic scanning electron microscopy (cryo-SEM), optical microscopy, fluorescence microscopy, etc. The results showed that both hydrophobic MSNPs and hydrophilic AONPs are adsorbed together at the water-oil interface to stabilize the W/O emulsion, which can be prepared by 500 rpm stirring. The stability of emulsions strongly depends on the wettability of MSNPs, and the MSNP with moderate hydrophobicity (for example, aqueous phase contact angle of 136°) makes the emulsion exhibit the highest stability against aggregation and settling at elevated temperatures. The emulsion stabilization mechanism was revealed in terms of the adsorption capacity of the surfactant by MSNPs, the adsorption morphology and desorption energy of nanoparticles at the water-oil interface adsorption layer, and emulsion rheology. These findings demonstrate a novel and simple strategy to prepare Pickering W/O emulsions with high-temperature stability at low shear strength.

Temperature-Insensitive Nonpolar Suspensions of Polyoxyethylene Alkyl Ether-Grafted Silica Nanoparticles

Nonpolar suspensions of organically modified particles exhibit a strong temperature sensitivity owing to the high-temperature-induced desorption/decomposition and the low-temperature-induced disorder/order conformational transition of the modifiers. This strong temperature sensitivity limits their applications, such as lubricants and oil-based drilling fluids, which require the suspensions to operate over a wide temperature range (e.g., 0-200 °C). We hypothesize that the introduction of a flexible ethylene oxide (EO) chain into the modifiers can disrupt the low-temperature-induced ordered conformation to improve the stability of the nonpolar suspensions. In this article, nonpolar suspensions with temperature insensitivity in the range of 5-160 °C were obtained via the covalent modification of silica NPs and the introduction of EO chains into the modifier molecules. Here, octadecyl-grafted silica NPs (C18-SiO2) and polyoxyethylene alkyl ether-grafted silica NPs (AEOn-SiO2) were synthesized and subsequently dispersed in mineral oil. The rheological properties of each suspension at different temperatures were evaluated, and the thermal stability of AEOn-SiO2 in mineral oil was investigated along with the conformational changes of the grafted chains. In the temperature range of 5-160 °C, the apparent viscosity and gel strength of the C18-SiO2 suspension changed dramatically, whereas the AEOn-SiO2 suspensions exhibited constant rheological properties over this temperature range. This temperature insensitivity of AEOn-SiO2 suspensions is attributed to the excellent thermal stability of AEOn-SiO2 in mineral oil and the disordered conformation of the EO chains upon cooling. This study provides a novel approach to preparing temperature-insensitive nonpolar suspensions, which have potential applications in the petroleum and lubricant industries.

Removal of Organic Dyes, Polymers and Surfactants Using Carbonaceous Materials Derived from Walnut Shells

A series of new granular carbonaceous adsorbents was prepared via single-stage physical and chemical activation of walnut shells. Their suitability for removing various types of organic pollutants (represented by dyes, surfactants and water-soluble polymers) from the liquid phase was assessed. The activation of the precursor was carried out with CO2 and H3PO4 using conventional heating. Activated biocarbons were characterized in terms of chemical composition, acidic-basic nature of the surface, textural and electrokinetic properties as well as thermal stability. Depending on the type of activating agent used during the activation procedure, the obtained biocarbons differed in terms of specific surface area (from 401 to 1361 m2/g) and the type of porous structure produced (microporosity contribution in the range of 45-75%). Adsorption tests proved that the effectiveness of removing organic pollutants from the liquid phase depended to a large extent on the type of prepared adsorbent as well as the chemical nature and the molecular size of the adsorbate used. The chemically activated sample showed greater removal efficiency in relation to all tested pollutants. Its maximum adsorption capacity for methylene blue, poly(acrylic acid), poly(ethylene glycol) and Triton X-100 reached the levels of 247.1, 680.9, 38.5 and 61.8 mg/g, respectively.

Effect of Shear History on Solid-Liquid Transition of Particulate Gel Fuels

Investigating the structural evolution of particulate gels is a very challenging task due to their vulnerability and true flow characteristics. In this work, deeper insight into the rheological properties of gel fuels filled with fumed silica (FS) and aluminum microparticles (Al MPs) was gained by changing shear procedures. Firstly, the flow curves were found to no longer follow the monotonic power law and exhibited subtle thixotropic responses. As the shear rate increased, the gel structure underwent a transition from local shear to bulk shear in the nonlinear region after yielding. This finding reveals the prevalence of nonideal local shear in industry. Secondly, the time-dependent rheological responses demonstrated that the strength spectrum of gel fuels depends on the applied shear rate, with stress relaxation more easily observed at lower shear rates. Those results involved the structural disruption, recovery, and equilibrium of particulate gels from two scales of shear rate and shear time.

A review of different frying oils and oleogels as alternative frying media for fat-uptake reduction in deep-fat fried foods

Purpose

This review aims to examine the potential of oleogels as a frying medium to decrease oil absorption during deep-frying and enhance the nutritional and energy content of foods. By investigating the factors influencing oil incorporation during deep-frying and examining the application of oleogels in this process, we seek to provide insights into using oleogels as an alternative to traditional cooking oils.

Scope

Deep-frying, a widely used cooking method, leads to the retention of large amounts of oil in fried food, which has been associated with health concerns. To address this issue, researchers have investigated various methods to minimize oil absorption during frying. One promising approach is the use of oleogels, which are thermo-reversible, three-dimensional gel networks formed by entrapment of bulk oil with a low concentration (<10% of weight) of solid lipid materials known as oleogelators. This review will focus on the following aspects: a) an overview of deep-fried foods, b) factors influencing oil uptake and underlying mechanisms for oil absorption during deep-frying, c) the characterization and application of different frying oils and their oleogels in deep-fried foods, d) components of the oleogel system for deep-frying, and e) the health impact, oxidative stability, and sensory acceptability of using oleogels in deep-frying.

Key findings

The review highlights the potential of oleogels as a promising alternative frying medium to reduce fat absorption in deep-fried foods. Considering the factors influencing oil uptake during deep-frying, as well as exploring the properties and applications of different frying oils and their oleogels, can result in improved product qualities and heightened consumer acceptance. Moreover, oleogels offer the advantage of lower fat content in fried products, addressing health concerns associated with traditional deep-frying methods. The capacity to enhance the nutritional and energy profile of foods while preserving sensory qualities and oxidative stability positions oleogels as a promising choice for upcoming food processing applications.

Simultaneous rheology and cure kinetics dictate thermal post-curing of thermoset composite resins for material extrusion

Thermoset composites are excellent candidates for material extrusion because they shear thin during extrusion but retain their shape once deposited via a yield stress. However, thermal post-curing is often required to solidify these materials, which can destabilize printed parts. Elevated temperatures can decrease the rheological properties responsible for stabilizing the printed structure before crosslinking solidifies the material. These properties, namely the storage modulus and yield stress, must therefore be characterized as a function of temperature and extent of reaction for various filler loadings. This work utilizes rheo-Raman spectroscopy to measure the storage modulus and dynamic yield stress as a function of temperature and conversion in epoxy-amine resins with fumed silica mass fractions up to 10 %. Both rheological properties are sensitive to conversion and particle loading, but only the dynamic yield stress is reduced by elevated temperatures early in the cure. Notably, the dynamic yield stress increases with conversion well before the chemical gel point. These findings motivate a two-step cure protocol that starts at a low temperature to mitigate the drop in dynamic yield stress, then ramps up to a high temperature when the dynamic yield stress is no longer at risk of decreasing to rapidly drive conversion to near completion. The results suggests that structural stability can be improved without resorting to increasing filler content, which limits control over the final properties, laying the groundwork for future studies to evaluate the stability improvements provided by the multi-step curing schedules.

Are all poorly soluble drugs dissolved in deep eutectic solvents true solutions?

HYPOTHESIS

The ability of deep eutectic solvents (DES) to enhance solubility of poorly soluble drugs has attracted increasing attention. Researchers have shown that drugs could be dissolved well in DES. In this study, we propose a new existence state of drugs in DES: a quasi-two-phase colloidal system.

EXPERIMENTS

Six poorly soluble drugs were used as the models. The formation of colloidal systems was observed visually by the Tyndall effect and DLS. TEM and SAXS were performed to obtain their structure information. The intermolecular interactions between components were probed via DSC and ¹H¹H-ROESY. In addition, the properties of colloidal systems were further studied.

FINDINGS

Our key finding is that several drugs like lurasidone hydrochloride (LH) could form stable colloids in [Th (thymol)] - [Da (decanoic acid)] DES, resulting from weak interactions between drugs and DES, which is different from the true solution of drugs like ibuprofen where strong interactions were formed. In this LH-DES colloidal system, DES solvation layer was directly observed on the surface of drug particles. In addition, the colloidal system with polydispersity shows superior physical and chemical stability. Different to the prevailing view that substances are fully dissolved in DES, this study discovers another existence state as stable colloidal particles in DES.

Thermal and Rheological Properties of Hydrophobic Nanosilica in Sunflower Oil Suspensions at High Pressures

Nowadays, the reduction of the environmental impact associated with the operation of the oil industry is a primary concern. A growing trend is to develop low-toxicity formulations based on biodegradable components. In this sense, vegetable oils structured with nanomaterials could be an alternative to mineral or synthetic oils for sustainable fluid formulations. Hydrophobic fumed silica nanoparticles have the capability to change the rheological behavior of oil in suspensions, providing a large variety of non-Newtonian behaviors over a wide range of temperatures, from shear-thinning to gel-like, depending on the concentration and the nanosilica’s hydrophobicity, that permits the design of fluids with selected characteristic and applications. This work explores the microstructure and the rheological behavior of hydrophobic fumed silica dispersed in a sunflower oil as a function of temperature and pressure. The results suggest that the suspensions of hydrophobic silica in sunflower oil reveals appropriate rheological and thermal properties over a wide range of temperatures and pressures to serve as components of sustainable drilling fluids.

Oleogel-Based Systems for the Delivery of Bioactive Compounds in Foods

Oleogels are semi-solid materials containing a large fraction of liquid oil entrapped in a network of structuring molecules. In the food industry, these formulations can be used to mimic fats and to deliver bioactive compounds. In the last decade, there has been increasing interest in these structures, not only from a scientific point of view, i.e., studying new molecules, methodologies for gelification, and new structures, but also from a technological point of view, with researchers and companies exploring these structures as a way to overcome certain challenges and/or create new and innovative products. One of the exciting applications of oleogels is the delivery of functional molecules, where the incorporation of oil-soluble functional compounds can be explored not only at the macroscale but also at micro- and nanoscales, resulting in different release behaviors and also different applications. This review presents and discusses the most recent works on the development, production, characterization, and applications of oleogels and other oleogel-based systems to deliver functional molecules in foods.

Methyl-grafted silica nanoparticle stabilized water-in-oil Pickering emulsions with low-temperature stability

HYPOTHESIS

The viscosity of water-in-oil Pickering emulsions may dramatically increase upon cooling. The solvation of the long-chain alkyl groups grafted on the particles stabilizer is the likely cause of the strong dependence of rheological property on temperature. Thus, we hypothesize that silica nanoparticles (NPs) grafted with short-chain alkyl groups can stabilize Pickering emulsions, yielding weakly temperature-dependent rheological property.

EXPERIMENTS

Using alkyl-grafted (methyl, octyl, and octadecyl) silica NPs as emulsifiers, the rheological properties and microstructure of the water-in-oil Pickering, as well as the solvation of the silica NPs, were studied using diffusing-wave spectroscopy microrheology measurements, confocal laser scanning microscopy, and low-field nuclear magnetic resonance measurements.

FINDINGS

The use of methyl- and octadecyl-grafted silica NPs, which have almost identical optimum contact angles, to stabilize emulsions dramatically reduced the effect of cooling on the viscosity. Moreover, the emulsions stabilized by these methyl-grafted silica NPs exhibited nearly constant rheological properties as the temperature decreased from 75 to 5 °C. The nearly constant rheological properties are attributed to the nearly constant solvation in this temperature range. These materials have potential applications in the cosmetics and petroleum industries.

Fabrication of Oleogels via a Facile Method by Oil Absorption in the Aerogel Templates of Protein-Polysaccharide Conjugates

In this study, a novel and facile method was developed to fabricate oleogels. The alginate/soy protein conjugates with excellent emulsifying activity and emulsion stability were prepared via Maillard reaction and freeze-dried to form the aerogel templates, which were then immersed in corn oil within 6 h to induce the oleogels. Compared with the alginate and soy protein solutions, the viscosity and elastic modulus G' of the conjugate solutions increased, indicating the formation of a new macromolecule and strengthened gel network from Maillard reaction. The conjugate aerogels presented the morphology of serious aggregation and conglutination but the higher elastic modulus and better thermal stability, due to the increasing covalent interactions. These aerogel templates showed a good oil absorption of up to 10.89 g/g aerogel and holding capacity of 40%. The resulting oleogels loaded with thymol showed excellent antimicrobial activities against Staphylococcus aureus and Escherichia coli. This work suggests that the fabrication of oleogels is not limited to the choice of existing oleogelators but from a wide variety of protein-polysaccharide conjugates to form the aerogel templates for oil absorption.

Reactive Mesoporous pH-Sensitive Amino-Functionalized Silica Nanoparticles for Efficient Removal of Coomassie Blue Dye

In this work, new smart mesoporous amine-functionalized silica nanoparticles were prepared from hydrolyzing microgels based on N-isopropyl acrylamide-co-vinyltrimethoxysilane microgels with tetraethoxysilicate and 3-aminopropyltriethoxysilane by sol-gel method. The thermal stability and Fourier transform infrared were used to determine the amine contents of the silica nanoparticles. The pH sensitivity of the synthesized silica nanoparticles in their aqueous solutions was evaluated by using dynamic light scattering (DLS) and zeta potential measurements. The porosity of the amine-functionalized silica nanoparticles was evaluated from a transmittance electron microscope and Brunauer-Emmett-Teller (BET) plot. The results have positively recommended the pH-sensitive amine-functionalized silica nanoparticles as one of the effective nano-adsorbent to remove 313 mg·g⁻¹ of CB-R250 water pollutant.

Influence of particle concentration on multiple droplet formation in Pickering emulsions

HYPOTHESIS

Multiphase droplets form when oil and water are mixed together at the ambivalent conditions that occur close to phase inversion. In this paper we propose a mechanism for the stabilisation of multiphase droplets by a single population of particles.

EXPERIMENTS

We investigated the microstructure of emulsions formed when dodecane and water are mixed in the presence of hydrophobic fumed silica nanoparticles. We identified the range of compositions, mixing times and rates where water-in-oil-in-water emulsions are stabilised in a single mixing step. To explore how the particle availability and mixing conditions lead to multiple emulsion formation we used light scattering and microscopy techniques to probe the size and morphology of the drops, and the particle coverage of the interfaces.

FINDINGS

Our key finding is that to stabilise multiphase drops there should be sufficient particles available to coat water drops that are entrained within coalescing oil droplets. The size of an entrained drop is determined by the volume of the rupturing film that forms between the oil drops. The particle coating prevents the entrained drop from escaping into the external aqueous phase. These results suggest a simple route for controlling the formation and stability of multiple emulsions for encapsulation applications.

Design of gel structures in water and oil phases for improved delivery of bioactive food ingredients

Gels are viscoelastic systems built up with a liquid phase entrapped in a three-dimensional network, which can behave as carriers for bioactive food ingredients. Many attempts have been made to design gel structures in the water phase (hydrogels, emulsion gels, bigels) or oil phase (organogels, bigels) in order to improve their delivery performances. Hydrogels are originated from proteins or polysaccharides, which are suitable for the delivery of hydrophilic ingredients. Organogels are mainly built up with the self-assembling of gelator molecules in the oil phase, and they offer good carriers for lipophilic ingredients. Emulsion gels and bigels, containing both aqueous and oil domains, can provide accommodations for lipophilic and hydrophilic ingredients simultaneously. Gel structures (e.g. rheology, texture, water holding capacity, swelling ratio) can be modulated by choosing different gelators, modifying gelation techniques, and the involvement of other ingredients (e.g. oils, emulsifiers, minerals, acids), which then alter the diffusion and release of the bioactive ingredients incorporated. Various studies have proved that gel-based delivery systems are able to improve the stability and bioavailability of many bioactive food ingredients. This review provides a state-to-art overview of different gel-based delivery systems, highlighting the significance of structure-functionality relationship, to provide advanced knowledge for the design of novel functional foods.