Preparation of positively charged oil/water nano-emulsions with a sub-PIT method

Development of ophthalmic nanoemulsions of β-caryophyllene for the treatment of Acanthamoeba keratitis

Although rare, amoebic keratitis (AK) is a disease caused by Acanthamoeba spp. that can lead to blindness. The drugs currently available for its treatment are very toxic, which has motivated the investigation for more effective and safe therapeutic options. In this study, the in vitro activity of ß-caryophyllene (BCP) was exploited taking into account its action against other protozoans as well as its well-known healing and anti-inflammatory properties (aspects relevant for the AK pathogenesis). On the other hand, high volatilization and oxidation phenomena are found for this compound, which led to its incorporation into nanoemulsions (NEs). Two emulsifying agents were tested, resulting in monodisperse systems with reduced droplet size (<265 nm) and high surface charge (positive and negative for NEs prepared with cetrimonium bromide -CTAB and Phosal® 50+, respectively). NEs prepared with CTAB were shown to be more stable after long-term storage at 4 and 25 °C than those prepared with Phosal®. Pure BCP, at the highest concentration (500 µM), resulted in a level of inhibition of Acanthamoeba trophozoites equivalent to that of reference drug (chlorhexidine). This activity was even greater after oil nanoencapsulation. The reduced droplet size could improve the interaction of the oil with the microorganism, justifying this finding. Changes in surface charge did not impact the activity. Positively charged NEs improved the interaction and retention of BCP in the cornea and thus should be prioritized for further studies.

Enzyme-assisted polysaccharides extraction from Calocybe indica: Synergistic antibiofilm and oxidative stability of essential oil nanoemulsion

Recently, mushroom polysaccharides have been explored to attribute to vital biologically important functions, and several extraction techniques can be employed, therefore, polysaccharides were extracted from the edible mushroom Calocybe indica to explore its functionality. Multiple enzymes viz., cellulase, pectinase, and protease (1:1:1) at temperature 47 °C and pH 4.64 with an extraction time of 2 h yielded 7.24 % polysaccharide content. The thermograph curve of polysaccharides showed two-stage decomposition at a different temperature range and decomposition of polysaccharides initiated with an onset temperature of 226.77 °C and a maximum peak at 248.90 °C. Hydrodistillation processed Eucalyptus globulus leaf oil was characterized using the chromatography technique and eucalyptol, p-cymene, Γ-terpinene, 4-epi-cubebol, spathulenol, viridiflorol, and p-mentha-1,5-dien-8-ol was observed as major components. As well, we formulated nanoemulsion using mushroom polysaccharide and eucalyptus leaf oil with 140.8 nm and evaluated synergistic antimicrobial and antibiofilm activity. MIC and MBC values for Pseudomonas aeruginosa, E. coli, and S. typhi were 12.50-3.125 and 6.25-1.56, and for S. aureus were 6.25, 6.25, 3.125, and 3.125, 3.125, 1.56 and for C. albicans the values were 12.50,12.50, 6.250 and 6.25,6.25, and 3.125 μl/mL respectively. The polysaccharides, essential oil, and nanoemulsion showed remarkable antibiofilm activity against S.aureus with inhibition of 57.42 ± 0.19, 59.62 ± 0.15, and 69.34 ± 0.19 %, while E. coli showed the least antibiofilm activity. However, all three tested samples showed significant (p < 0.05) differences against tested pathogenic microorganisms with inhibition of biofilm formation. Therefore, it could be inferred that the synergistic properties of essential oils with mushroom polysaccharides are a promising strategy to enhance antimicrobial efficacy and control foodborne pathogens.

Preparation of Stable Phase Change Material Emulsions for Thermal Energy Storage and Thermal Management Applications: A Review

Thermal energy storage (TES) is an important means for the conservation and efficient utilization of excessive and renewable energy. With a much higher thermal storage capacity, latent heat storage (LHS) may be more efficient than sensible heat storage. Phase change materials (PCMs) are the essential storage media for LHS. PCM emulsions have been developed for LHS in flow systems, which act as both heat transfer and thermal storage media with enhanced heat transfer, low pumping power, and high thermal storage capacity. However, two major barriers to the application of PCM emulsions are their instability and high degree of supercooling. To overcome these, various strategies have been attempted, such as the reduction of emulsion droplet size, addition of nucleating agents, and optimization of the formulation. To the best of our knowledge, however, there is still a lack of review articles on fabrication methods for PCM emulsions or their latest applications. This review was to provide an up-to-date and comprehensive summary on the effective strategies and the underlying mechanisms for the preparation of stable PCM emulsions and reduction of supercooling, especially with the organic PCMs of paraffin. It was also to share our insightful perspectives on further development and potential applications of PCM emulsions for efficient energy storage.

Advances of spontaneous emulsification and its important applications in enhanced oil recovery process

Emulsions, including oil-in-water (O/W) and water-in-oil (W/O) emulsions, can play important roles in both controlling reservoir conformance and displacing residual oil for enhanced oil recovery (EOR) projects. However, current methods, like high-shear mixing, high-pressure homogenizing, sonicators and others, often use lots of extra energy to prepare the emulsions with high costs but very low energy efficiency. In recent decades, spontaneous emulsification methods, which allow one to create micro- and nano-droplets with very low or even no mechanical energy input, have been launched as an overall less expensive and more efficient alternatives to current high extra energy methods. Herein, we primarily review the basic concepts on spontaneous emulsification, including mechanisms, methods and influenced parameters, which are relevant for fundamental applications for industrials. The spontaneity of the emulsification process is influenced by the following variables: surfactant structure, concentration and initial location, oil phase composition, addition of co-surfactant and non-aqueous solvent, as well as salinity and temperature. Then, we focus on the description of importance for emulsions in EOR processes from advances and categories to improving oil recovery mechanisms, including both sweep efficiency and displacement efficiency aspects. Finally, we systematically address the applications and outlooks based on the use of spontaneous emulsification in the practical oil reservoirs for EOR processes, in which conventional, heavy, high-temperature, high-salinity and low-permeability oil reservoirs, as well as wastewater treatments after EOR processes are involved.

Synthesis of Nano/Microsized MIL-101Cr Through Combination of Microwave Heating and Emulsion Technology for Mixed-Matrix Membranes

Nano/microsized MIL-101Cr was synthesized by microwave heating of emulsions for the use as a composite with Matrimid mixed-matrix membranes (MMM) to enhance the performance of a mixed-gas-separation. As an example, we chose CO₂/CH₄ separation. Although the incorporation of MIL-101Cr in MMMs is well-known, the impact of nanosized MIL-101Cr in MMMs is new and shows an improvement compared to microsized MIL-101Cr under the same conditions and mixed-gas permeation. In order to reproducibly obtain nanoMIL-101Cr microwave heating was supplemented by carrying out the reaction of chromium nitrate and 1,4-benzenedicarboxylic acid in heptane-in-water emulsions with the anionic surfactant sodium oleate as emulsifier. The use of this emulsion with the phase inversion temperature (PIT) method offered controlled nucleation and growth of nanoMIL-101 particles to an average size of <100 nm within 70 min offering high apparent BET surface areas (2,900 m² g^-1) and yields of 45%. Concerning the CO₂/CH₄ separation, the best result was obtained with 24 wt.% of nanoMIL-101Cr@Matrimid, leading to 32 Barrer in CO₂ permeability compared to six Barrer for the neat Matrimid polymer membrane and 21 Barrer for the maximum possible 20 wt.% of microMIL-101Cr@Matrimid. The nanosized filler allowed reaching a higher loading where the permeability significantly increased above the predictions from Maxwell and free-fractional-volume modeling. These improvements for MMMs based on nanosized MIL-101Cr are promising for other gas separations.

The influence of organically intercalated montmorillonites on the interfacial tension and structure of oil-in-water nanoemulsions

The properties of O/W emulsions can be improved by the addition of nanomaterials. To explore the influence of organically intercalated montmorillonites (OMts) on the properties of O/W emulsions, we introduced an OMt into a nanoemulsion as a co-stabilizer with the quaternary ammonium Gemini cationic surfactant (G16-2-16) and nonionic lauryl polyoxyethylene ether (Brij 30). The influence of the organically intercalated montmorillonite (OMt) on the properties, such as the interfacial tension, zeta potential, stability, conductivity and morphology of the droplets, of the nanoemulsions was investigated. The results indicate obvious synergistic effects of OMt with G16-2-16. At the concentration of 0.15% w/v G16-2-16, ultralow interfacial tension (IFT) of the O/W results in the formation of nanoemulsions in a much shorter time with 3.4 × 10^-3% w/v OMt than that in the case of without OMt; however, at the concentration of 0.2% w/v G16-2-16, the interfacial tension of the O/W increased upon the addition of 3.4 × 10^-3% w/v OMt. In addition, light transmission measurements showed that the transmission of the nanoemulsions varied with temperature, and the process was reversible. The mechanisms of these phenomena were analyzed and confirmed by TEM.

Anion amphiphilic random copolymers and their performance as stabilizers for O/W nanoemulsions

A series of anionic amphiphilic random copolymers with sodium p-styrene sulfonate and dodecyl methacrylate were synthesized via free radical polymerization and their property in the formation and stabilization of nano-emulsions were investigated.

Effective charges and zeta potentials of oil in water microemulsions in the presence of Hofmeister salts

We present a theory which allows us to calculate the effective charge and zeta potential of oil droplets in microemulsions containing Hofmeister salts. A modified Poisson-Boltzmann equation is used to account for the surface and ion polarizations and hydrophobic and dispersion interactions. The ions are classified as kosmotropes and chaotropes according to their Jones-Dole viscosity B coefficient. Kosmotropes stay hydrated and do not enter into the oil phase, while chaotropes can adsorb to the oil-water interface. The effective interaction potentials between ions and oil-water interface are parametrized so as to accurately account for the excess interfacial tension.

Improving emulsion formation, stability and performance using mixed emulsifiers: A review

The formation, stability, and performance of oil-in-water emulsions may be improved by using combinations of two or more different emulsifiers, rather than an individual type. This article provides a review of the physicochemical basis for the ability of mixed emulsifiers to enhance emulsion properties. Initially, an overview of the most important physicochemical properties of emulsifiers is given, and then the nature of emulsifier interactions in solution and at interfaces is discussed. The impact of using mixed emulsifiers on the formation and stability of emulsions is then reviewed. Finally, the impact of using mixed emulsifiers on the functional performance of emulsifiers is given, including gastrointestinal fate, oxidative stability, antimicrobial activity, and release characteristics. This information should facilitate the selection of combinations of emulsifiers that will have improved performance in emulsion-based products.

Transitional phase inversion of emulsions monitored by in situ near-infrared spectroscopy

Water-heptane/toluene model emulsions were prepared to study emulsion transitional phase inversion by in situ near-infrared spectroscopy (NIR). The first emulsion contained a small amount of ionic surfactant (0.27 wt % of sodium dodecyl sulfate) and n-pentanol as a cosurfactant. In this emulsion, the study was guided by an inversion coordinate route based on a phase behavior study previously performed. The morphology changes were induced by rising aqueous phase salinity in a "steady-state" inversion protocol. The second emulsion contained a nonionic surfactant (ethoxylated nonylphenol) at a concentration of 3 wt %. A continuous temperature change induced two distinct transitional phase inversions: one occurred during the heating of the system and another during the cooling. NIR spectroscopy was able to detect phase inversion in these emulsions due to differences between light scattered/absorbed by water in oil (W/O) and oil in water (O/W) morphologies. It was observed that the two model emulsions exhibit different inversion mechanisms closely related to different quantities of the middle phases formed during the three-phase behavior of Winsor type III.

Highly stable concentrated nanoemulsions by the phase inversion composition method at elevated temperature

Oil-in-water nanoemulsions were produced in the system water/Span 80-Tween 80/paraffin oil via the phase inversion composition (PIC) method at elevated temperature. With the increase of preparation temperature from 20 to 70 °C, we found that the emulsion droplet diameter decreases from 10.3 μm to 51 nm, proving the formation of nanoemulsions. The viscosity of nanoemulsions clearly increases with droplet volume fraction, φ, but the droplet size changes less. Significantly, at φ ≤ 0.5, the size distribution of nanoemulsions can be kept unchangeable more than 5 months. These results proved that the highly viscous paraffin oil can hardly be dispersed by the PIC method at 25 °C, but the increase in preparation temperature makes it possible for producing monodisperse nanoemulsions. Once the nanoemulsion is produced, the stability against Ostwald ripening is outstanding due to the extremely low solubility of the paraffin oil in the continuous phase. The highly stable nanoemulsions are of great importance in practical applications.

Preparation and optimization of PIT solid lipid nanoparticles via statistical factorial design

The objective of this study was the preparation, physico-chemical characterization and statistical optimization of cationic solid lipid nanoparticles (SLN) prepared by the PIT method as potential carrier for gene therapy, emphasizing the application of factorial design in such a kind of studies. The preliminary screening from a physico-chemical point of view on three cationic lipids (CTAB, DDAB and DOTAP), selected on the basis of their different chemical structure and increasing lipophilicity, allowed us to select SLN with DOTAP, due to its higher zeta potential and smaller particle size. Afterward, a 2(2) full factorial experimental design was developed in order to study the effects of two independent variables (amount of DOTAP and concentration of lipid matrix) and their interaction on mean particle size and zeta potential values. The factorial planning was validated by ANOVA analysis; the correspondence between the predicted values of size and zeta and those measured experimentally confirmed the validity of the design and the equation applied for its resolution. The factorial design showed a significant influence of the independent variables on the selected parameters; in particular, a higher effect of DOTAP was observed on zeta potential value. Different dilutions of the optimized SLN containing 7% w/w of cutina CP and 1% w/w of DOTAP, with size and zeta potential values respectively of 462.9 nm and 50.8 mV, were in vitro examined to evaluate the possible cytotoxicity on two models of cell cultures: human prostate cancer androgen-non-responsive DU-145 cells and primary cultures of rat astrocytes.