Enhanced stability, formulations, and rheological properties of nanoemulsions produced with microfludization for eco-friendly process

HYPOTHESIS

Eco-friendly processes that are emerging around the world require mass production of low-energy, low-cost nanoemulsions. The process involving the high-concentrated nanoemulsions and diluting them with a large amount of solvent can certainly save the cost; however, not much detailed research has been conducted on the stability mechanism and rheological characteristics of high-concentrated nanoemulsions.

EXPERIMENTS

In this study, we produced nanoemulsions via the microfluidization (MF) process, comparing their dispersion stability and rheological characteristics with macroemulsions across various oil and surfactant concentrations. Droplet mobility and dispersion stability depended on these concentrations, with Asakura-Osawa-type attractive depletion considering interparticle interaction's role in stability changes. We investigated nanoemulsions' long-term stability based on turbidity and droplet size changes over four weeks, proposing a stability diagram showing four different states depending on emulsification conditions.

FINDINGS

We explored the microstructure of emulsions under varying mixing conditions, observing their effects on droplet mobility and rheological properties. We monitored changes in rheology, turbidity, and droplet size over 4 weeks, establishing stability diagrams for macro- and nanoemulsions. The stability diagrams revealed that the stability of emulsions are sensitively dependent on the droplet size, concentrations, surfactant cocentrations and the strcture of coexistent phases in case of macroscopic segregation are significantly different depending on the droplet sizes. We identified their respective stability mechanisms and discovered the relationship between stability and rheological properties for highly concentrated nanoemulsion.

Microalgae harvesting using colloidal gas aphrons generated from single and mixed surfactants

Harmful algal blooms (HABs) caused by microalgae are becoming increasingly common and pose serious threats to human health, aquaculture, and marine environments and, therefore, their removal is becoming essential. Colloidal gas aphrons (CGAs), a recent technology adapted in flotation, showed promise in removing several contaminants from aqueous solutions. This study aimed to investigate the potency of CGAs in removing several microalgae strains (Spirulina platensis, Nannochloropsis oculata, and Chlorella vulgaris) from aqueous solutions. Surfactants, including cationic hexadecyl trimethyl ammonium bromide (HTAB), anionic sodium dodecylbenzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), and their mixes, were used to prepare stable CGAs. The effect of different environmental parameters like algae concentration, pH, and salinity, on removing Spirulina platensis was thoroughly investigated. Operating conditions, including surfactant type, flotation time, flowrate, and solution temperature, were optimized. At pH 5 and 50 °C, Spirulina platensis, Chlorella vulgaris, and mixed microalgae were fully removed using CGAs produced from cationic HTAB surfactant. About 95% removal of Nannochloropsis oculata was achieved using mixed surfactant CGAs. The results obtained from this work demonstrated the promising potential of CGAs produced from both single and mixed surfactants in harvesting various microalgae from aqueous media.

Pure and mixed aqueous micellar solutions of Sodium Dodecyl sulfate (SDS) and Dimethyldodecyl Amine Oxide (DDAO): Role of temperature and composition

Aqueous mixtures of anionic and nonionic/cationic surfactants can form non-trivial self-assemblies in solution and exhibit macroscopic responses. Here, we investigate the micellar phase of pure and mixed aqueous solutions of Sodium Dodecyl Sulfate (SDS) and Dimethyldodecyl Amine Oxide (DDAO) using a combination of Small Angle Neutron Scattering (SANS), Fourier-Transform Infrared Spectroscopy (FTIR) and rheological measurements. We examine the effect of temperature (0-60 °C), on the 20 wt% SDS micellar solutions with varying DDAO (⩽5 wt%), and seek to correlate micellar structure with zero-shear solution viscosity. SANS establishes the formation of prolate ellipsoidal micelles in aqueous solutions of pure SDS, DDAO and SDS/DDAO mixtures, whose axial ratio is found to increase upon cooling. Elongation of the ellipsoidal micelles of pure SDS is also induced by the introduction of the non-anionic DDAO, which effectively reduces the repulsive interactions between the anionic SDS head-groups. In FTIR measurements, the formation of elongated mixed ellipsoidal micelles is confirmed by the increase of ordering in the hydrocarbon chain tails and interaction between surfactant head-groups. We find that the zero-shear viscosity of the mixed surfactant solutions increases exponentially with decreasing temperature and increasing DDAO content. Significantly, a master curve for solution viscosity can be obtained in terms of micellar aspect ratio, subsuming the effects of both temperature and DDAO composition in the experimental range investigated. The intrinsic viscosity of mixed micellar solutions is significantly larger than the analytical and numerical predictions for Brownian suspensions of ellipsoidal colloids, highlighting the need to consider interactions of soft micelles under shear, especially at high concentrations.

Applicability of an anionic-nonionic surfactant in p-cresol contaminated soil washing: Finding the optimal mixing ratio

In this study, the parameters influencing p-cresol removal efficiency in soil washing method were investigated. Primarily, extraction efficiencies of three Tween series surfactants (Tween 20, Tween 60, Tween 80) with 10 mM concentration were compared. Tween 80 showed the best results since its value (55%) was 4% and 13% higher than that of Tween 60 and Tween 20. The impact of mixed surfactant on extraction rate was examined by employing a mixture of Tween 80 and one anionic surfactant (sodium dodecyl sulfate) with different molar ratio as the main washing solution. The results denoted that the molar ratio of 3:2 (SDS:Tween80) could enhance the extraction rate up to 38% compared to using SDS and Tween 80 alone. Regarding the initial p-cresol concentration in the collected sample, the cleanup level (390 mg/kg) could only be achieved using the mixed-surfactant. Thus, the minimum required surfactant concentrations to hit the target level was calculated to be 3.54 g/L of Tween 80 and 2.105 g/L of SDS (molar ratio of 0.27 SDS:Tween80). Studying the role of surfactant concentration indicated that its increment from 10 mM to 20 mM, which is way above all the reagents' critical micelle concentration (CMC), does not affect the removal rate considerably. The same results were obtained comparing the effect of washing time in three different levels (30 min, 60 min and 90 min). However, temperature showed to be a more significant parameter as it could enhance the results up to 20% (for SDS).

Optimization of mixed surfactants-based β-carotene nanoemulsions using response surface methodology: An ultrasonic homogenization approach

In the present study, food grade mixed surfactant-based β-carotene nanoemulsions were prepared without using any co-surfactant. Response surface methodology (RSM) along with central composite design (CCD) was used to investigate the effect of independent variables (surfactant concentration, ultrasonic homogenization time and oil content) on response variables. RSM analysis results revealed that experimental results were best fitted into a quadratic polynomial model with regression coefficient values of more than 0.900 for all responses. Optimized preparation conditions for β-carotene nanoemulsions were 5.82% surfactant concentration, 4 min ultrasonic homogenization time and 6.50% oil content. The experimental values at optimized preparation conditions were 119.33 nm droplet size, 2.67p-Anisidine value and 85.63% β-carotene retention. This study will be helpful for the fortification of aqueous products with β-carotene.

Skin permeation of D-limonene-based nanoemulsions as a transdermal carrier prepared by ultrasonic emulsification

Nanoemulsions can be used for transporting pharmaceutical phytochemicals in skin-care products because of their stability and rapid permeation properties. However, droplet size may be a critical factor aiding permeation through skin and transdermal delivery efficiency. We prepared D-limonene nanoemulsions with various droplet sizes by ultrasonic emulsification using mixed surfactants of sorbitane trioleate and polyoxyethylene (20) oleyl ether under different hydrophilic-lipophilic balance (HLB) values. Droplet size decreased with increasing HLB value. With HLB 12, the droplet size was 23 nm, and the encapsulated ratio peaked at 92.3%. Transmission electron microscopy revealed spherical droplets and the gray parts were D-limonene precipitation incorporated in spherical droplets of the emulsion system. Franz diffusion cell was used to evaluate the permeation of D-limonene nanoemulsion through rat abdominal skin; the permeation rate depended on droplet size. The emulsion with the lowest droplet size (54 nm) achieved the maximum permeation rate. The concentration of D-limonene in the skin was 40.11 μL/cm(2) at the end of 360 min. Histopathology revealed no distinct voids or empty spaces in the epidermal region of permeated rat skin, so the D-limonene nanoemulsion may be a safe carrier for transdermal drug delivery.