Special Issue "Micro/Nano Emulsions: Smart Colloids for Multiple Applications"

A special issue of Nanomaterials (ISSN 2079-4991). This special issue belongs to the section "Synthesis, Interfaces and Nanostructures".

Deadline for manuscript submissions: closed (31 July 2021).

Special Issue Editor

Prof. Dr. Ruggero Angelico
E-Mail Website
Guest Editor
Department of Agricultural, Environmental and Food Sciences, University of Molise, I-86100 Campobasso, Italy
Interests: physicochemical properties of condensed matter at macro-, micro- and nanometer scale: surfactant systems, equilibrium phase behavior, and non-equilibrium phase transitions; micro- and macroemulsions, self-association in liquid–crystals, molecular diffusion modeling, and scattering techniques; colloidal dispersions in shear flow, rheology of soft materials
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Special Issue Information

Dear Colleagues,

Microemulsions are continuously attracting the interest of researchers due to their unique properties, such as ultralow interfacial tension between oil and water phases, large interfacial area, thermodynamic stability, and ability to solubilize otherwise immiscible liquids. They are colloidal fluids containing one surfactant film, classified as oil-in-water (o/w), water-in-oil (w/o) or bicontinuous systems depending on their microstructure. The shape of the aggregates can be spherical, rod-like, and even worm-like, all of them characterized by having at least one dimension of about 10–100 nm. Some of the numerous applications of microemulsions relate to their potential uses as drug delivery systems, for the design of new composite materials, personal care and cleaning products, pharmaceutical formulations, chemical reaction media, and in the art restoration and petrochemical industry.

Nanoemulsions are kinetically stable liquid dispersions, consisting only of nanodroplets with sizes of a few hundred nm. Although they do not form spontaneously but are obtained by mechanical force, nanoemulsions are widespread in the food, pharmaceutical, and personal care industries due to their unique physicochemical properties and functional attributes, such as high surface area per unit volume, transparent appearance, tunable rheology, and advanced bioavailability.

I warmly invite scholars involved in the Colloids and Surface Science research areas to contribute original research papers as well as review articles to this Special Issue, in order to give the readers of Nanomaterials an updated and new perspective of these versatile colloidal systems for all kinds of applications, including both small- and large-scale processes.

Prof. Dr. Ruggero Angelico
Guest Editor

Manuscript Submission Information

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Keywords

  • microstructure
  • micro-emulsion
  • nanoemulsion
  • titration method
  • droplet size
  • emulsifier
  • micelle
  • high-pressure homogenization
  • microfluidization
  • ultrasonic emulsification

Published Papers (9 papers)

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Research

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Article
Influence of Chymosin on Physicochemical and Hydrolysis Characteristics of Casein Micelles and Individual Caseins
Nanomaterials 2021, 11(10), 2594; https://doi.org/10.3390/nano11102594 - 01 Oct 2021
Viewed by 569
Abstract
The effects of chymosin on the physicochemical and hydrolysis characteristics of casein micelles and individual caseins were investigated. Adding 0.03 units of chymosin/mL led to the casein micelles in skim milk coagulating after a 3 h incubation period at 30 °C. SDS–PAGE investigation [...] Read more.
The effects of chymosin on the physicochemical and hydrolysis characteristics of casein micelles and individual caseins were investigated. Adding 0.03 units of chymosin/mL led to the casein micelles in skim milk coagulating after a 3 h incubation period at 30 °C. SDS–PAGE investigation showed that β-CN, κ-CN, αs-CN, and a portion of β-lactoglobulin (β-LG) in the milk supernatant fraction (MSF) were precipitated into the milk pellet fraction (MPF). The mean particle size of the MSF with chymosin decreased from 254.4 nm to 179.2 nm after a 3 h incubation period. Mass spectrometry and SDS–PAGE analysis suggested that chymosin hydrolyzed individual β-CN, κ-CN, and αs-CN, but not β-LG. Chymosin hydrolysis led to a decrease in the molecular weights of the hydrolyzed β-CN, κ-CN, and αs-CN. Particle size analysis indicated that there was no difference in the particle size distribution of hydrolyzed β-CN and αs-CN. Moreover, our outcomes demonstrated that the hydrolysis of κ-CN by chymosin occurs before that of β-CN and αs-CN. Full article
(This article belongs to the Special Issue Micro/Nano Emulsions: Smart Colloids for Multiple Applications)
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Article
Phase Inversion and Interfacial Layer Microstructure in Emulsions Stabilized by Glycosurfactant Mixtures
Nanomaterials 2021, 11(2), 331; https://doi.org/10.3390/nano11020331 - 27 Jan 2021
Viewed by 909
Abstract
Identification of strategies to prolong emulsion kinetic stability is a fundamental challenge for many scientists and technologists. We investigated the relationship between the emulsion stability and the surfactant supramolecular organization at the oil–water interface. The pseudo-phase diagrams of emulsions formed by water and, [...] Read more.
Identification of strategies to prolong emulsion kinetic stability is a fundamental challenge for many scientists and technologists. We investigated the relationship between the emulsion stability and the surfactant supramolecular organization at the oil–water interface. The pseudo-phase diagrams of emulsions formed by water and, alternatively, a linear or a branched oil, stabilized by mixtures of two sugar-based surfactants, Span80 and Tween80, are presented. The surfactant ordering and dynamics were analyzed by electron paramagnetic resonance (EPR) spectroscopy. In Oil-in-Water (O/W) emulsions, which are stable for more than four days, disordered surfactant tails formed a compact and viscous layer. In Water-in-Oil (W/O) emulsions, whose stability is much lower, surfactants formed an ordered layer of extended tails pointing toward the continuous apolar medium. If linear oil was used, a narrow range of surfactant mixture composition existed, in which emulsions did not demix in the whole range of water/oil ratio, thus making it possible to study the phase inversion from O/W to W/O structures. While conductometry showed an abrupt inversion occurring at a well-defined water/oil ratio, the surfactant layer microstructure changed gradually between the two limiting situations. Overall, our results demonstrate the interconnection between the emulsion stability and the surfactant layer microstructuring, thus indicating directions for their rational design. Full article
(This article belongs to the Special Issue Micro/Nano Emulsions: Smart Colloids for Multiple Applications)
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Article
Bioinspired Nanoemulsions Stabilized by Phosphoethanolamine and Phosphoglycerol Lipids
Nanomaterials 2020, 10(6), 1185; https://doi.org/10.3390/nano10061185 - 18 Jun 2020
Cited by 2 | Viewed by 1029
Abstract
Water-in-oil (W/O) nanoemulsions stabilized by phospholipids (PLs) are increasingly exploited in a wide spectrum of applications, from pharmaceuticals to food and cosmetic formulations. In this work, we report the design and optimization of an innovative emulsion based on a mixture of phosphoethanolamine (PE) [...] Read more.
Water-in-oil (W/O) nanoemulsions stabilized by phospholipids (PLs) are increasingly exploited in a wide spectrum of applications, from pharmaceuticals to food and cosmetic formulations. In this work, we report the design and optimization of an innovative emulsion based on a mixture of phosphoethanolamine (PE) and phosphoglycerol (PG) PLs, inspired by the composition of the inner leaflet of a bacterial outer membrane. Using the natural oil squalene as the continuous organic phase, no additional emulsion stabilizer is needed. On the other hand, a small amount of Span 80 is required when dodecane is used. The obtained nanoemulsions are stable for at least two hours, thus allowing the droplet size and distribution to be characterized by Dynamic Light Scattering (DLS) and the lipid layer structure and dynamics to be analyzed by Electron Paramagnetic Resonance (EPR) spectroscopy. The results indicate that squalene shallowly intercalates among the lipid tail termini, being unable to deeply penetrate the adsorbed lipid monolayer. The altered lipid dynamics are proposed to be the reason for the enhanced emulsion stability, this paving the way to future implementations and possible applications. Full article
(This article belongs to the Special Issue Micro/Nano Emulsions: Smart Colloids for Multiple Applications)
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Article
Interfacial and Bulk Stabilization of Oil/Water System: A Novel Synergistic Approach
Nanomaterials 2020, 10(2), 356; https://doi.org/10.3390/nano10020356 - 18 Feb 2020
Cited by 4 | Viewed by 1207
Abstract
Oil/water emulsions are usually stabilized either by interfacial modification using nanoparticles and surfactants (stated as pickering emulsion or bijels) or by bulk stabilization with the help of low-molecular-weight or polymeric gelators (known as bigels) in response to some external stimuli (e.g., pH, temperature). [...] Read more.
Oil/water emulsions are usually stabilized either by interfacial modification using nanoparticles and surfactants (stated as pickering emulsion or bijels) or by bulk stabilization with the help of low-molecular-weight or polymeric gelators (known as bigels) in response to some external stimuli (e.g., pH, temperature). Both these approaches result in different systems that are quite useful for different applications, including catalysis, pharmaceutical and agrochemicals. However, these systems also possess some inherent drawbacks that need to be addressed, like difficulty in fabrication and ensuring the permanent binding of nanoparticles at the oil/water interface, in case of nanoparticles stabilized emulsions (i.e., interfacial stabilization). Similarly, the long-term stability of the oil/water systems produced by using (hydro/organo) gelators (i.e., bulk stabilization) is a major concern. Here, we show that the oil/water system with improved mechanical and structural properties can be prepared with the synergistic effect of interfacial and bulk stabilization. We achieve this by using nanoparticles to stabilize the oil/water interface and polymeric gelators to stabilize the bulk phases (oil and water). Furthermore, the proposed strategy is extremely adaptable, as the properties of the resultant system can be finely tuned by manipulating different parameters such as nanoparticles content and their surface functionalization, solvent type and its volume fraction, and type and amount of polymeric gelators. Full article
(This article belongs to the Special Issue Micro/Nano Emulsions: Smart Colloids for Multiple Applications)
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Article
Two-Dimensional Clusters of Colloidal Particles Induced by Emulsion Droplet Evaporation
Nanomaterials 2020, 10(1), 156; https://doi.org/10.3390/nano10010156 - 16 Jan 2020
Cited by 3 | Viewed by 1220
Abstract
The minimization principle of the second moment of the mass distribution (M2) is responsible for the unique structure of three-dimensional clusters by using emulsion droplet evaporation. Herein we study the structure of two-dimensional clusters of colloidal particles bound at the [...] Read more.
The minimization principle of the second moment of the mass distribution ( M 2 ) is responsible for the unique structure of three-dimensional clusters by using emulsion droplet evaporation. Herein we study the structure of two-dimensional clusters of colloidal particles bound at the interface of liquid droplets in the plane. We found that, differently from the three-dimensional system, the two-dimensional clusters have multiple degenerate configurations (isomers). An interesting feature of such two-dimensional clusters is that they have the same packings as those belonging to a class of geometric figures known as polyiamonds. In particular, except for the six-particle cluster, many higher order clusters of polyiamond have not been reported previously. Using a simple geometrical approach, based on the number of ways to generate a packing, we calculated the occupation probabilities of distinct isomeric clusters. The level of agreement with the results of metropolis Monte Carlo simulations was good for clusters containing up to nine particles, suggesting that our two-dimensional cluster structures are not a result of the minimization of the second moment. In addition, the structure of these clusters is somewhat insensitive to the range and depth of the interparticle potential, in good agreement with the results in the literature. Full article
(This article belongs to the Special Issue Micro/Nano Emulsions: Smart Colloids for Multiple Applications)
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Review

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Review
Foray into Concepts of Design and Evaluation of Microemulsions as a Modern Approach for Topical Applications in Acne Pathology
Nanomaterials 2020, 10(11), 2292; https://doi.org/10.3390/nano10112292 - 19 Nov 2020
Cited by 3 | Viewed by 1050
Abstract
With a fascinating complexity, governed by multiple physiological processes, the skin is considered a mantle with protective functions which during lifetime are frequently impaired, triggering dermatologic disorders. As one of the most prevalent dermatologic conditions worldwide, characterized by a complex pathogenesis and a [...] Read more.
With a fascinating complexity, governed by multiple physiological processes, the skin is considered a mantle with protective functions which during lifetime are frequently impaired, triggering dermatologic disorders. As one of the most prevalent dermatologic conditions worldwide, characterized by a complex pathogenesis and a high recurrence, acne can affect the patient’s quality of life. Smart topical vehicles represent a good option in the treatment of a versatile skin condition. By surpassing the stratum corneum known for diffusional resistance, a superior topical bioavailability can be obtained at the affected place. In this direction, the literature study presents microemulsions as a part of a condensed group of modern formulations. Microemulsions are appreciated for their superior profile in matters of drug delivery, especially for challenging substances with hydrophilic or lipophilic structures. Formulated as transparent and thermodynamically stable systems, using simplified methods of preparation, microemulsions have a simple and clear appearance. Their unique structures can be explained as a function of the formulation parameters which were found to be the mainstay of a targeted therapy. Full article
(This article belongs to the Special Issue Micro/Nano Emulsions: Smart Colloids for Multiple Applications)
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Review
Microemulsion Microstructure(s): A Tutorial Review
Nanomaterials 2020, 10(9), 1657; https://doi.org/10.3390/nano10091657 - 24 Aug 2020
Cited by 27 | Viewed by 2280
Abstract
Microemulsions are thermodynamically stable, transparent, isotropic single-phase mixtures of two immiscible liquids stabilized by surfactants (and possibly other compounds). The assortment of very different microstructures behind such a univocal macroscopic definition is presented together with the experimental approaches to their determination. This tutorial [...] Read more.
Microemulsions are thermodynamically stable, transparent, isotropic single-phase mixtures of two immiscible liquids stabilized by surfactants (and possibly other compounds). The assortment of very different microstructures behind such a univocal macroscopic definition is presented together with the experimental approaches to their determination. This tutorial review includes a necessary overview of the microemulsion phase behavior including the effect of temperature and salinity and of the features of living polymerlike micelles and living networks. Once these key learning points have been acquired, the different theoretical models proposed to rationalize the microemulsion microstructures are reviewed. The focus is on the use of these models as a rationale for the formulation of microemulsions with suitable features. Finally, current achievements and challenges of the use of microemulsions are reviewed. Full article
(This article belongs to the Special Issue Micro/Nano Emulsions: Smart Colloids for Multiple Applications)
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Review
Synthesis and Technology of Nanoemulsion-Based Pesticide Formulation
Nanomaterials 2020, 10(8), 1608; https://doi.org/10.3390/nano10081608 - 17 Aug 2020
Cited by 22 | Viewed by 2394
Abstract
Declines in crop yield due to pests and diseases require the development of safe, green and eco-friendly pesticide formulations. A major problem faced by the agricultural industry is the use of conventional agrochemicals that contribute broad-spectrum effects towards the environment and organisms. As [...] Read more.
Declines in crop yield due to pests and diseases require the development of safe, green and eco-friendly pesticide formulations. A major problem faced by the agricultural industry is the use of conventional agrochemicals that contribute broad-spectrum effects towards the environment and organisms. As a result of this issue, researchers are currently developing various pesticide formulations using different nanotechnology approaches. The progress and opportunities in developing nanoemulsions as carriers for plant protection or nanodelivery systems for agrochemicals in agricultural practice have been the subject of intense research. New unique chemical and biologic properties have resulted in a promising pesticide nanoformulations for crop protection. These innovations—particularly the nanoemulsion-based agrochemicals—are capable of enhancing the solubility of active ingredients, improving agrochemical bioavailability, and improving stability and wettability properties during the application, thus resulting in better efficacy for pest control and treatment. All of these—together with various preparation methods towards a greener and environmentally friendly agrochemicals—are also discussed and summarized in this review. Full article
(This article belongs to the Special Issue Micro/Nano Emulsions: Smart Colloids for Multiple Applications)
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Review
The Role of Additives in Warm Mix Asphalt Technology: An Insight into Their Mechanisms of Improving an Emerging Technology
Nanomaterials 2020, 10(6), 1202; https://doi.org/10.3390/nano10061202 - 19 Jun 2020
Cited by 12 | Viewed by 1347
Abstract
The asphalt industry’s incentive to reduce greenhouse gas emissions has increased since the 1990s due to growing concerns on environmental issues such as global warming and carbon footprint. This has stimulated the introduction of Warm Mix Asphalt (WMA) and its technologies which serve [...] Read more.
The asphalt industry’s incentive to reduce greenhouse gas emissions has increased since the 1990s due to growing concerns on environmental issues such as global warming and carbon footprint. This has stimulated the introduction of Warm Mix Asphalt (WMA) and its technologies which serve the purpose of reducing greenhouse gas emissions by reducing the mixing and compaction temperatures of asphalt mix. WMA gained popularity due to the environmental benefit it offers without compromising the properties, performance and quality of the asphalt mix. WMA is produced at significantly lower temperatures (slightly above 100 °C) and thus results in less energy consumption, fewer emissions, reduced ageing, lower mixing and compaction temperatures, cool weather paving and better workability of the mix. The latter of these benefits is attributed to the incorporation of additives into WMA. These additives can also confer even better performance of WMA in comparison to conventional Hot Mix Asphalt (HMA) methods. Even though there are recommended dosages of several WMA additives, there is no general standardized mixture design procedure and this makes it challenging to characterize the mechanism(s) of action of these additives in the warm mix. The effects of the addition of additives into WMA are known to a reasonable extent but not so much is known about the underlying interactions and phenomena which bring about the mechanism(s) by which these additives confer beneficial features into the warm mix. Additives in a certain way are being used to bridge the gap and minimize or even nullify the effect of the mixing temperature deficit involved in WMA processes while improving the general properties of the mix. This review presents WMA technologies such as wax, chemical additives and foaming processes and the mechanisms by which they function to confer desired characteristics and improve the durability of the mix. Hybrid techniques are also briefly mentioned in this paper in addition to a detailed description of the specific modes of action of popular WMA technologies such as Sasobit, Evotherm and Advera. This paper highlights the environmental and technical advantages of WMA over the conventional HMA methods and also comprehensively analyzes the mechanism(s) of action of additives in conferring desirable characteristics on WMA, which ultimately improves its durability. Full article
(This article belongs to the Special Issue Micro/Nano Emulsions: Smart Colloids for Multiple Applications)
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