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Specific conductivity Ä of a typical microemulsion with a flexible film as function of the water volume fraction.
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In a previous work, we showed the extension of the microemulsion area towards highly or fully water dilutable systems by adding a short chain alcohol as cosolvent, like ethanol, to the system water/sodium oleate/citronellol/limonene. It was possible to convert an anti-percolative system to a percolative one by making the interfacial film more flexi...
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... the nano-structure and the film rigidity of a microemulsion, especially with ionic surfactants and water as polar phase. Two phenomena can be distinguished: Anti-percolative and percolative behaviour. Systems with a flexible interfacial film show typically bell-shaped evolution of the specific conductivity Ä with increasing amount of water (see Fig. ...
Citations
... The conclusions drawn remain valid to a certain extent when replacing water in microemulsions with some other polar solvents such as glycerol, alcohols or molten salts [48][49][50]. ...
Nano- and microemulsions are colloidal systems that are widely used in various fields of biomedicine, including wound and burn healing, cosmetology, the development of antibacterial and antiviral drugs, oncology, etc. The stability of these systems is governed by the balance of molecular interactions between nanodomains. Microemulsions as a colloidal form play a special important role in stability. The microemulsion is the thermodynamically stable phase from oil, water, surfactant and co-surfactant which forms the surface of drops with very small surface energy. The last phenomena determines the shortage time of all fluid dispersions including nanoemulsions and emulgels. This review examines the theory and main methods of obtaining nano- and microemulsions, particularly focusing on the structure of microemulsions and methods for emulsion analysis. Additionally, we have analyzed the main preclinical and clinical studies in the field of wound healing and the use of emulsions in cancer therapy, emphasizing the prospects for further developments in this area.
... Combining multiple solvents compounding can reduce the total amount of organic solvents used in microemulsions [41]. Surfactants and co-surfactants can regulate the hydrophilic-lipophilic balance (HLB) value of microemulsions and improve their flowability, thus making the oil-water interface layer more stable [42][43][44]. In addition, studies have shown that an excellent microemulsion should have a wide transparent temperature range (−5-60 • C) to ensure stability under any conditions [45]. ...
(1) Pine wilt disease (PWD) is a devastating disease of pine forests caused by the pine wood nematode (PWN), Bursaphelenchus xylophilus. Control of the disease is a worldwide problem due to the impossibility of using chemical nematicides on a large scale and for long periods. (2) Based on preliminary tests of microemulsion quality and stability, the optimum formulation was selected from 14 formulated microemulsions. The median lethal concentration (LC50) of the selected formulation at 48 h after treatment of B. xylophilus was 31.45 μg/mL of emamectin benzoate. The active ingredient reached the apical branches of Pinus thunbergii within 90 days of injection. (3) P. thunbergii was inoculated with B. xylophilus at 100 days post-injection, and the trees treated with the formulation remained uninfected for 450 days. Trunk injection exerted substantial control over PWD. (4) These results indicate that this formulation has the advantages of good transportability and long persistence in pine trees after injection and that it effectively prevents PWD. Therefore, this emamectin benzoate formulation can effectively reduce PWD occurrence in pine forests.
... Electrical conductivity is one of the commonly used methods to study microemulsions. During the polymerization of microemulsion system, the change trend of electrical conductivity can be divided into four stages [33,34]: the first stage is a slow increase of electrical conductivity, which is permeated due to the aggregation of reverse microemulsion droplets, at this time, W/O microemulsion system, its outer oil is slightly conductive or non-conductive. In the second stage, the conductivity increases linearly rapidly, and the microemulsions droplets fuse with each other due to the sticky collisions. ...
Polyacrylamide (PAM) was prepared by a new method of inverse microemulsion polymerization, with (NH4)2S2O8-Na2SO3 as initiator and liquid paraffin/Span80-Op10/AM-H2O-NaAc as polymerization system in this paper. The effects of initiator dosage, emulsifier dosage, monomer concentration, oil–water ratio, and temperature on molecular weight, electrical conductivity, particle size distribution, and monomer conversion were studied as well. The results indicate that that the more stable Polyacrylamide (PAM) polymer was prepared under the conditions of initiator dosage of 0.4~0.5%, emulsifier dosage of 55~60%, temperature of 40~45 °C, hydrophile–lipophile balance (HLB) value of 8.0~8.2, and NaAc concentration of 3%.
... It is evident that this ternary mixture with only EtOH as solubilizer is not completely water soluble as the biphasic region is too pronounced in the aqueous corner of the diagram. To diminish the solubility gap in the aqueous region, EtOH was mixed with different surfactants, as it is known that a mixture of EtOH with surfactants is able to extend the monophasic regimes of µEs (Klossek et al., 2013). Classical food-agreed surfactants used for the formulation of beverages amongst others are PEG-derivatives of Vitamin C, sucrose fatty acid esters, or polysorbates. ...
Mentha spicata L. disappears in winter. The lack of fresh mint during the cold season can be a limiting factor for the preparation of mint tea. A fresh taste source that can be kept during winter is mint essential oil. As the oil is not soluble in water, a food-approved, water-soluble essential oil microemulsion was studied, investigating different surfactants, in particular Tween® 60. The challenge was to dissolve an extremely hydrophobic essential oil in a homogeneous, stable, transparent, and spontaneously forming solution of exclusively edible additives without adulterating the original fresh taste of the mint. Making use of the microemulsions’ water and oil pseudo-phases, hydrophilic sweeteners and hydrophobic dyes could be incorporated to imitate mint leaf infusions aromatically and visually. The resulting formulation was a concentrate, consisting of ∼ 90% green components, which could be diluted with water or tea to obtain a beverage with a pleasant minty taste.
... When the rigidity of the interface is strong enough, as in the case of dodecanol or longer Guerbet alcohols, the microemulsion can be diluted no more, neither by water, nor by oil, a property that is specific to rigid microemulsions. 191 • UFMEs sporadically appeared since the 1970s, when they were typically called surfactant-free or detergentless microemulsions. 192 However, they had been neglected for a long time and became fully characterized by phase diagram, structure and thermodynamics only in 2011 with ethanol as hydrotrope, long after a pioneering study by Kunieda and Shinoda on the decane−water−isobutoxyethanol system. ...
... 73 Each industry has its own recipe: The main trick is to add to a "normal" cosolvent, e.g., some ethanol as second additive, which can "disappear" during dilution, still leaving the system as a microemulsion. That has been studied in detail by Kunz and co-workers with "green" nontoxic components only, in the system water/sodium oleate/ citronellol/limonene. 191 The extension of stability and dilutability of a microemulsion can be enhanced by adding osmolytes to the water phase, as osmolytes (sometimes here sweeteners are used) have the property to push the cosurfactant into the interfacial film, thus increasing stability as well as dilutability. 583 In that sense, there is a synergistic effect of sucrose and ethanol, which is used in the preparation of alcoholic beverages with high sugar content. ...
... Javanbakht et al. (2017) demonstrated that MEs could yield higher recovery of soil comparing to surfactant flooding. Klossek et al. (2013) suggested that single phase area in pseudo-ternary phase diagram was enhanced when adding ethanol into acid methyl ester-rapeseed biodiesel (oil phase) and sodium oleate (surfactant), which was favorable for reducing surface tension. With these in mind, it is hypothesized that MEs containing biodiesel, surfactants and other additives can present advantages in removal of PAHs from contaminated soils over other reported agents. ...
Microemulsion (ME) is considered as a stable solution for adsorbing organic matters. Aiming to remediate PAH contaminated soils from industrial sites in Shijiazhuang (Soil CPS) and Beijing (Soil CSG) in China, novel MEs were designed with different ratios of mixed surfactants (Surf, TX-100+Tween 80), n-butanol and fatty acid methyl esters (FAMEs). Particle size, transmittance, surface intension, Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy of the MEs were analyzed. PAH removals by solubilization experiments were studied and regeneration of waste ME was evaluated. Results showed the novel MEs were obtained with particle sizes in a range of 18.53 to 122.77 nm. The lowest surface intension of MEs was 26.53 mN/m, which was prone to PAHs transferring to MEs. -OH (3350 cm⁻¹), -C=C (1740 cm⁻¹) and -C-O (1072 cm⁻¹) functioned in forming MEs. Additionally, -OH, C-H, -C=C, -C-O were considered as active binding sites when remediating PAH soils. PAH removals in soils CPS and CSG were up to 90.1% and 89.7% with surfactants and co-surfactant (Surf:Co-s), (Surf:Co-s) and FAME, soil and MEs (w:v) at ratios of 1:1, 8:2 and 1:4, respectively. About 85.6% of FAME and 41.9% of TX-100 in waste ME were recovered for recycle purpose.
... Characteristics of microemulsion (a) and the mechanism of upgrading biodiesel (b), adapted from ref.150 .The most common structures in microemulsions are droplets, either water-in-oil (w/o) or oil-in-water (o/w)151 . The solubilization and stabilization mechanism of the water/diesel/bio-oil microemulsion could be explained by the "like dissolves like" theory150 . ...
Biodiesel is a mixture of fatty acid alkyl esters (FAAE) produced by transesterification, which has been promoted as a substitute for petroleum diesel in some areas of China. However, it shows poor cold flow properties (CFPs), such as high pour point, high cloud point, and high cold filter plugging point, meaning the biodiesel would crystalize under low-temperature conditions, thus resulting in engine problems and emission issues. This article focused on the mechanisms related to the CFPs of biodiesel and outlined the factors that initialize and accelerate the crystallization process. The influence of CFPs on engine performance and pollutant emissions was also discussed. Particular emphasis was given to available methods that can improve the CFPs of biodiesel. Modifying FAAEs' composition, changing the component ratio, and removing minor constituents are three primary directions. Every derivative method was described in detail about the characteristics, shortcomings, and what can be improved. The type and load of cloud point/pour point/cold filter plugging point cold flow improvers were compared and selected on the basis of the improvement effect of CFPs. Microemulsion is a new method that may be used to improve the CFPs of biodiesel. Due to the variability of the biodiesel components and the complexity of each improving method on the overall fuel properties and performance, the CFPs modification methods should be studied and evaluated carefully and comprehensively before being adopted in industrial applications.
... μE structure plays very an important role in drug release system. μE-based DDSs include the oral, nasal, and transdermal, digestive tract administration that depends upon the disease type and release of drug active ingredient efficiently on target area [15][16][17][18][19][20][21][22][23][24]. ...
Microemulsions (μEs)-based drug delivery is known to be superior as well as effective due to customizable and easy management, efficiency and capability, and quick drug absorption over a wide range of targets. Herein, two μE formulations were established comprising of clove oil (as oil phase), water (as aqueous phase), Tween-80 (as surfactant), isopropanol, and methanol (as cosurfactant) for formulation A (μE-A) and formulation B (μE-B), respectively, and further used for the encapsulation of an antimuscarinic drug, mirabegron (MBG). Multiple complementary measurements, namely, electrical conductivity (σ), viscosity (η), and optical microscopy, show the existence of phase transition from W/O to O/W μE via intermediate bicontinuous channels. MBG showed long storage stability as well as good solubility i.e. 3.0 and 2.5 wt% at pH 6.4 in optimum μE-A and μE-B, respectively. Furthermore, no apparent aggregation of MBG was observed, as revealed by scanning transmission electron microscopy and peak correlations of IR analysis, suggesting the stability of MBG inside the formulations. Likewise, fluorescence detection senses the interfacial environment of MBG molecules in the examined formulations that could be vital for understanding the mechanism of controlled drug release.
Structural Dynamics of Tween-Based Microemulsions for Antimuscarinic Drug Mirabegron
... This can largely be minimized with concomitant addition of short chain cosurfactants. Studies show that cosurfactant, typically short chain alcohols, glycols and ethers (≈4 carbon atoms), expand the single-phase region and facilitate greater oil incorporation [12,18]. In an oil-in-water (o/w) μE, cosurfactant partitions into oil and decreases the spontaneous mean curvature to ultimately create a more fluid interface. ...
... Employing this mechanism, it acts as hydrotrope to break the rigid gel and liquid crystalline structures [19,20]. Driven by the relative polarity, cosurfactant distributes between the oil and surfactant tail, and reduces the interfacial tension close to zero [18]. As a result, μE area expands and interface is rendered less vulnerable to dilution. ...
... Aggregates (secondary peaks in A) probably originated from surfactant excess at low oil concentration. It underscores the requirement of a cut-off dispersed phase concentration for initiating the development of μE structures [18]. Marginal swelling (≈12−16 nm) is evident at intermediate oil incorporation (14-22 %). ...
This study reports a detailed characterization of a nonionic microemulsion (μE) composed of n-butylacetate/α-tocopheryl polyethylene glycol succinate (TPGS)/alcohol/water. Two approaches of expanding the monophasic area were explored; (i) addition of Pluronic® 123 (P123) in aqueous phase, and (ii) use of short chain alcohol (CnHn+1OH; n = 2-4) as cosurfactant. Pseudo-ternary phase diagrams were constructed using water titration method. Characterizations were performed using dynamic light scattering (DLS), differential scanning calorimetry (DSC), small angle neutron scattering (SANS) and electron microscopic techniques. DSC and SANS results showed gradual structural transformation from water-in-oil to oil-in-water system. The optimized formulation (oil/Smix/water - 19/40/41) showed average hydrodynamic diameter of 22 nm, consistent with electron microscopic observations. Ethanol (EtOH), with its high fluidity and smaller headgroup area, offered maximum expansion in the phase boundary. Surfactant unimers, derived from EtOH-driven de-micellization, reinforced the interface and solubilized the incoming oil molecules. Oil incorporation was accompanied with improved loading of carbamazepine, a hydrophobic drug. Except marginal swelling, no significant microstructural changes were noticed during water dilution (≈90%) and salt addition (0.9% NaCl) in the optimized μE formulation. A linear increase in oil incorporation was noticed upon adding propylene glycol as a cosolvent.
... On the other hand, medium-chain alcohols form stable oil droplets within the system, with less sign of phase separation [60]. The selection of the co-surfactant can control the release of the drug by tailoring the viscosity of the NE to either low or high viscosity, without compromising the stability of the NE [61]. The inclusion of alcohol in the formulation exerts a strong influence on the density and viscosity of the NE. ...
Nanoemulsions (NEs) are colloidal dispersions of two immiscible liquids, oil and water, in which one is dispersed in the other with the aid of a surfactant/co-surfactant mixture, either forming oil-in-water (o/w) or water-in-oil (w/o) nanodroplets systems, with droplets 20–200 nm in size. NEs are easy to prepare and upscale, and they show high variability in their components. They have proven to be very viable, non-invasive, and cost-effective nanocarriers for the enhanced transdermal delivery of a wide range of active compounds that tend to metabolize heavily or suffer from undesirable side effects when taken orally. In addition, the anti-microbial and anti-viral properties of NE components, leading to preservative-free formulations, make NE a very attractive approach for transdermal drug delivery. This review focuses on how NEs mechanistically deliver both lipophilic and hydrophilic drugs through skin layers to reach the blood stream, exerting the desired therapeutic effect. It highlights the mechanisms and strategies executed to effectively deliver drugs, both with o/w and w/o NE types, through the transdermal way. However, the mechanisms reported in the literature are highly diverse, to the extent that a definite mechanism is not conclusive.
