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Controlled Wet Chemical Synthesis of Multifunctional Nanomaterials: Current Status and Future Possibility
Published in Surender Kumar Sharma, Nanohybrids in Environmental & Biomedical Applications, 2019
Navadeep Shrivastava, Surender Kumar Sharma
A microemulsion is a thermodynamically stable dispersion of two immiscible liquids (e.g., water and oil) with the aid of a surfactant. Small droplets of one liquid are stabilized in the other liquid by an interfacial film of surfactant molecules. In water-in-oil microemulsions, the aqueous phase forms droplets (~1–50 nm in diameter) in a continuous hydrocarbon phase. Consequently, this system can impose kinetic and thermodynamic constraints on particle formation, such as a nanoreactor. The surfactant-stabilized nanoreactor provides confinement that limits particle nucleation and growth. By mixing two identical water-in-oil emulsions containing the desired reactants, the droplets will collide, coalesce and split, and induce the formation of precipitates (see Figure 1.1b). Adding a solvent like ethanol to the microemulsion allows the extraction of the precipitate by filtering or centrifuging the mixture. The main advantage of the reverse micelle or emulsion method is better control over the nanoparticles’ size by varying the nature and amount of surfactant and co-surfactant, the oil phase or the other reacting conditions. The working window for synthesis in microemulsions is usually quite narrow and the yield of nanoparticles is low compared to other methods, such as hydrothermal and co-precipitation methods. Furthermore, because large amounts of solvent are necessary to synthesize appreciable amounts of material, microemulsion is not a very efficient process and is rather difficult to scale-up (Liu et al., 2008; Kharissova et al., 2013).
Macro- and Microemulsion Technology and Trends
Published in Chester L. Foy, David W. Pritchard, and Adjuvant Technology, 2018
Creation of a large Wd can often be achieved by using a combination of ionic surfactant (anionic or zwitter ionic/pseudo ionic) and an insoluble (water insoluble) fatty derivative or a cosolvent/coemulsifier, preferably an emulsifier that would form a complex with the first component. Thus, in general, a microemulsion consists of at least five components (water, oil, surfactant, coemulsifier, and cosolvent). For agricultural formulations, active ingredients form the additional components. Design and formation of a microemulsion is essentially a process of orientation of the molecules at the interface towards a state of γij → 0 and Wd → maximum positive value. Thus, once the ME is prepared, it is considered infinitely stable, since a true ME is a thermodynamically stable system.
Formulation of a Stable Microemulsion Slug for Enhanced Oil Recovery in the Upper Assam Basin
Published in Subrata Borgohain Gogoi, Advances in Petroleum Technology, 2020
Shilpi Sarmah, Subrata Borgohain Gogoi, Fan Xianfeng
The exploration of microemulsions commenced in 1943. In 1959, Schulman and his colleagues constructed the term ‘microemulsion’. Moreover, microemulsions contribute a significant part in our daily-use products like cosmetic products and pharmaceutical products [66]. Furthermore, the debate about the development of microemulsions like the oil-dispersed-in-water (o/w) or water-dispersed-in-oil (w/o) systems has been discussed in the past years. The common elements that the dispersions have are oil phase, aqueous phase, surfactant and co-surfactant. The critical micelle concentration (CMC) acts as an important parameter for a stable microemulsion. The criteria which influence the CMC are surfactant structure, electrolyte presence, presence of organic additives, presence of a second liquid phase and temperature [65]. Winsor nominated a strategy for a stable microemulsion formulation with oil, water and surfactants. There are four types of Winsor classification: Winsor type I (an oil phase and a water phase with dissolved surfactants), Winsor type II (an oil phase with dissolved surfactants and a water phase), Winsor type III (a middle phase with oil, surfactants and water; an excess water phase; and an excess oil phase) and Winsor type IV (mixture of oil, water and surfactants) [64]. The middle phases of Winsor type III systems and Winsor type IV systems were considered as microemulsions due to their thermodynamic stability. Practically, it is not simple to identify the microemulsion on the basis of the Winsor classification strategy because the system is mixed. Centrifugation is the solution for this issue because it can aid in accelerating the equilibration [67].
Investigation on the formation and stability of microemulsions with Gemini surfactants: DPD simulation
Published in Journal of Dispersion Science and Technology, 2023
Haixia Zhang, Zhenxing Zhu, Zongxu Wu, Fang Wang, Bin Xu, Shoulong Wang, Lijuan Zhang
Microemulsion is a homogeneous dispersion system consisted of oil and water as the inner or external phase, surfactant as an emulsifier and cosurfactants. Microemulsions are divided to three types, water-in-oil (W/O), oil-in-water(O/W), and bicontinuous,[1] according to the composition of the inner phase. Recently, microemulsions have attracted increasing attentions, due to the interesting properties of transparency, the simplicity of manufacture, thermodynamic stability and high-solubilization capacity for both lipophilic and hydrophilic compounds. Microemulsions have extensive applications in foods, cosmetics, pharmaceuticals and petroleum industry. For example, it could increase the bioavailability and solubility of many drug molecules in different application systems.[2–9]
Microemulsion and microemulsion gel formulation for transdermal delivery of rutin: Optimization, in-vitro/ex-vivo evaluation and SPF determination
Published in Journal of Dispersion Science and Technology, 2022
Azar Kajbafvala, Alireza Salabat
Microemulsions are thermodynamically stable and isotropic clear dispersions of oil, water and surfactant mixtures with 10 − 100 nm droplets size.[11] Microemulsions have been used in various fields such as drug delivery, catalysts, polymer composites, agriculture, food, fuel additives, cosmetics, paints and pharmaceutics.[12–16] Both hydrophilic and lipophilic drugs may be delivered by microemulsions and their gels. By the way of several different mechanisms e.g., the presence of surfactant and co-surfactant as permeation enhancers, being a co-solubilizer for poorly soluble drugs, wide interfacial region due to the small droplet sizes, and suitable wetting ability, microemulsions can improve drug permeation through stratum corneum and drug penetration to the deeper layers.[1, 17] Unfortunately, low viscosity of microemulsions would restrict their topical use. To overcome this problem, the use of a gelling agent would be a proper choice. The microemulsion components can affect significantly its formation and characteristics.[18] For understanding the influence of the formulation component on microemulsion formation and gaining an optimal formulation quickly for drug-loaded microemulsion with good characteristics and release behavior, a statistical experimental design with a D-optimal mixture design was used in this study.
Remediation of Oil-contaminated Sediments Using Microemulsions: A Review
Published in Soil and Sediment Contamination: An International Journal, 2021
Suelem Dela Fonte, Cibele Silva, Luiz Carlos Santos, George Simonelli
In physical methods, techniques such as steam extraction or thermal heating can remedy contaminated sediments. In general, contaminated sediments are removed from the place of origin for the treatment (Dhaliwal et al. 2019; Song et al. 2017). Biological methods bring solutions associated with the use of bacteria and fungi for the decomposition of hydrocarbons (Song et al. 2017). Chemical treatments aim to remove contaminants through the action of chemical substances such as surfactants, solvents, or microemulsified systems (Ossai et al. 2020; Song et al. 2017). Remediation can also occurby combining methods. In recent years, the number of studies on sediment remediation using microemulsions has increased. Microemulsions (ME) are thermodynamically stable mixtures composed of an oily phase, an aqueous phase, surfactant, and, sometimes, cosurfactant. In general, these mixtures are transparent or translucent (Hernandez, Ehlert, and Trabelsi 2019). Dantas et al. (2012), Hernandez, Ehlert, and Trabelsi (2019), Tolmacheva et al. (2017), and Wang et al. (2019a) used ME to treat contaminated soil and sand. The studies showed that all ME analyzed were able to remove hydrocarbons or derivatives from the sediments.