Non-aqueous Emulsions Research Articles

Bottlebrush Random Copolymers at Oil‐Oil Interfaces

Comprehensive SummaryOil‐in‐oil nonaqueous emulsions are of great interest for developing emulsion‐templated polymers and encapsulation systems that are incompatible with water‐sensitive substances. Tailor‐made amphiphilic block copolymers are by far the most efficient stabilizers for oil‐in‐oil emulsions while less attention is given to copolymers with more complex architectures. Here, we report the stabilization of DMSO‐silicone oil interface by bottlebrush random copolymers (BRCPs) containing norbornene backbones with densely grafted poly(methyl methacrylate) (PMMA) and polystyrene (PS) side chains. The assembly kinetics of BRCPs at the DMSO‐silicone oil interface can be divided into three processes, including diffusion, reconfiguration and reorganization, and can be varied by tuning the degree of polymerization of the backbone (NB). Due to the high efficiency of BRCPs in reducing the interfacial tension, when using BRCPs as stabilizers, stable silicone oil‐in‐DMSO traditional emulsions and high internal phase emulsions (HIPEs) can be successfully obtained, while no stable emulsions can be achieved with linear PMMA‐b‐PS serving as the stabilizer. This study, for the first time, underscores the great potential of amphiphilic bottlebrush copolymers in preparing oil‐in‐oil emulsions. Given the advances in polymerization strategy, a broad variety of amphiphilic bottlebrush copolymers are expected to be synthesized and applied in the stabilization of nonaqueous biphasic systems.

Flexible and robust aramid/octadecane phase change materials from nonaqueous emulsion template towards efficient thermal storage and camouflage

Flexible and robust aramid/octadecane phase change materials from nonaqueous emulsion template towards efficient thermal storage and camouflage

Cell membrane-inspired regulation of reactant diffusion for active agent microencapsulation via interface engineering

Microencapsulation of hydrophilic amines in nonaqueous emulsions provides opportunities for a variety of applications, such as CO2 absorbents, and adhesives, but also presents challenges due to the intense reactant diffusion and disruptive interfacial reaction kinetics. Drawing inspiration from cellular systems, where cell membranes effectively regulate mass transfer for essential activities, we propose an interface engineering approach to manage interfacial reactant diffusion. This strategy obviates the modification of emulsion phases with additives in literature, which lowered effective core content. To achieve this, a solvent-induced polymer self-assembling method is adopted. The self-assembled polymer effectively formed a stabilizing viscoelastic film, which kinetically traps the microdroplets, serves as a viscous barrier lowering intense amine diffusion and interfacial polymerization kinetics, and provides protection for the microdroplets against the destructive forces from reaction turbulence and emulsion collision. This approach possesses high tolerance against microencapsulation conditions and is technically friendly, laying the groundwork for scalable microencapsulation of amines to meet industrial demands. We successfully synthesized Tetraethylenepentamine (TEPA)-loaded microcapsules with adjustable shell tightness, hierarchical shell structures, high shell strength and high core content. The method's versatility is further evidenced with different species containing reactive hydrogens. The demonstrated potential of TEPA-loaded microcapsules in effective CO2 capture and instant adhesives provides a fresh perspective on the microencapsulation of distinct polar payloads through interface engineering and its wide-ranging applications.

Microcapsule fabrication by ATRP at the interface of non-aqueous emulsions.

We present soft-template encapsulation of salt hydrate phase change materials (PCMs) using modified silica particles to both stabilize emulsions and serve as initiators for organocatalyzed photoredox ATRP. The resulting core-shell structures have high core loading and are robust to thermal cycling. Critically, this strategy eliminates the need for a reagent in the core phase, thus preserving purity, and offers the ability to tailor shell composition for desired applications.

Oil-in-oil droplet stability dependence on dimensions of 2D Pickering particles of controlled size

Control in 2D polymer particle size results in control over the droplet diameter and stability in oil-in-oil Pickering emulsions.

Highly stretchable phase change fibers from coaxial wet spinning of nonaqueous emulsions for temperature regulation

Although phase change fibers have proven to be highly potential for a variety of applications, the rigidity of solid–liquid phase change material in its solid state hinders the fabrication of highly stretchable phase change fibers. In this work, we report a strategy of encapsulating phase change material (octadecane, OD) in thermoplastic polyurethane (TPU) based on a nonaqueous emulsion (OD-in-TPU solution), which serves as the core layer liquid in coaxial wet spinning. The use of TPU solution as the outer layer liquid provides an extra cover for the core layer of TPU dispersed with OD. The resulting core-sheath structured phase change fibers exhibited excellent flexibility, stretchability and elasticity, with the tensile strain at break up to 623.9 % and ultimate stress up to 3.5 MPa. The fibers showed heat absorption and release temperatures ranging from 30.7 to 32.0 °C and from 21.6 to 22.3 °C, respectively, similar to that of bulk OD. In particular, the fibers possessed much reduced OD leakage in comparison to fibers from conventional methods, and the fibers exhibited extremely high heat capacity (up to 187.8 J/g), without obvious deterioration observed in heat capacity after 100 heating–cooling cycles. Simple fabrication, excellent stretchability, high heat capacity, and reusability enabled such phase change fibers to be highly promising for practical use in temperature regulation.

Encapsulation of hygroscopic liquids via polymer precipitation in non-aqueous emulsions

HypothesisEncapsulation of ionic liquids (ILs) and phase change materials (PCMs) can overcome limitations associated with bulk materials, e.g., slow mass transfer rates, high viscosities, or susceptibility to external environment. Single step soft-templated encapsulation methods commonly use interfacial polymerization for shell formation, with a multifunctional monomer in the continuous phase and another in the discontinuous phase, and thus do not give pristine core material. We posit that polymer precipitation onto emulsion droplets in non-aqueous emulsions could produce a robust shell without contamination of the core, ideal for the encapsulation of water-sensitive or water-miscible materials. ExperimentsSolutions of commodity polymers were added to the continuous phase of non-aqueous Pickering emulsions stabilized by alkylated graphene oxide (GO) nanosheets such that the change in solubility of the polymer led to formation of robust shells and the production of capsules that could be isolated. FindingsWe demonstrate that a polymer precipitation approach can produce capsules with pristine core of the IL 1-ethyl-3-methylimidazolium hexafluorophosphate [Emim][PF6] or the salt hydrate PCM magnesium nitrate hexahydrate (MNH) and shell of nanosheets and polystyrene, poly(methyl methacrylate), or polyethylene. The capsules are approximately 80 wt% [Emim][PF6] or >90 wt% MNH, and the core can undergo multiple cycles of solidification and melting without leakage or destruction. This novel, single-step methodology provides a distinct advantage to access capsules with pristine core composition and is amenable to different core and shell, paving the way for tailoring capsule composition for desired applications.

Nonaqueous Emulsion Polycondensation Enabled by a Self-Assembled Cage-like Surfactant.

Nonaqueous emulsions are crucial for a range of applications based on water‐sensitive systems such as controlled polymerizations requiring anhydrous reaction conditions and the stabilization of readily hydrolyzable reagents or pharmacologically active components. However, defined molecular surfactants to stabilize such nonaqueous emulsions are scarce. We introduce a self‐assembled coordination cage, decorated with cholesterol functionalities, to serve as a molecular surfactant for various oil‐in‐oil emulsions of immiscible organic solvents. While the positively charged cage forms the amphiphile's polar moiety, the non‐polar cholesterol appendices can bend in a common direction to stabilize the emulsion. Templated by the droplets, polycondensation reactions were carried out to produce microstructured polyurethane and polyurea materials of different particle sizes and morphologies. Further, the amphiphilic cage can encapsulate a guest molecule and the resulting host‐guest assembly was also examined as a surfactant. In addition, the aggregation behavior of the amphiphilic cage in an aqueous medium was examined.

Copper substituted methyl ammonium lead bromide grown using Non-Aqueous emulsion based synthesis technique

Hybrid organic–inorganic lead halide perovskites have become a promising material in the field of optoelectronics because of their prospects in the opto-electronics industry. However, the presence of the element “Lead” makes them legislatively untouchable for large scale production and human use. Herein, we report a non-aqueous emulsion-based synthesis and characterization of Copper (Cu)-substituted methyl ammonium lead Bromide (CH3NH3Pb1-xCuxBr3) perovskite nanoparticles which has not been reported previously. This technique enables the synthesis of quantum confined nanostructures by precipitation from the colloidal mixture. The structural characterization of all the samples showed that the crystallization occurs in the orthorhombic phase for the pristine and copper substituted methyl ammonium lead bromide nanostructure. The samples prepared with the precursor stoichiometry of CH3NH3Pb0.6Cu0.4Br3 and CH3NH3Pb0.5Cu0.5Br3 exhibited improved crystallinity relative to the un-substituted perovskite material. We report that as Cu content increases the average crystalline size increases which leads to decrease in optical band gap. The change in Cu content did not alter the excitonic absorption indicating that the quality of the material was not compromised as a result of the Cu substitution.

Solvent-Free Fabrication of Biphasic Lipid-Based Microparticles with Tunable Structure

Lipid-based biphasic microparticles are generally produced by long and complex techniques based on double emulsions. In this study, spray congealing was used as a solvent-free fabrication method with improved processability to transform water-in-oil non-aqueous emulsions into spherical solid lipid-based particles with a biphasic structure (b-MPs). Emulsions were prepared by melt emulsification using different compositions of lipids (Dynasan®118 and Compritol®888 ATO), surfactants (Cetylstearyl alcohol and Span®60) and hydrophilic carriers (PEGs, Gelucire®48/16 and Poloxamer 188). First, pseudo-ternary phase diagrams were constructed to identify the area corresponding to each emulsion type (coarse emulsion or microemulsion). The hydrophobicity of the lipid mostly affected the interfacial tension, and thus the microstructure of the emulsion. Emulsions were then processed by spray congealing and the obtained b-MPs were characterized in terms of thermal and chemical properties (by DSC and FT-IR), external and internal morphology (by SEM, CLSM and Raman mapping). Solid free-flowing spherical particles (main size range 200–355 µm) with different architectures were successfully produced: microemulsions led to the formation of particles with a homogeneous internal structure, while coarse emulsions generated “multicores-shell” particles consisting of variable size hydrophilic cores evenly distributed within the crystalline lipid phase. Depending on their composition and structure, b-MPs could achieve various release profiles, representing a more versatile system than microparticles based on a single lipid phase. The formulation and technological strategy proposed, provides a feasible and cost-effective way of fabricating b-MPs with tunable internal structure and release behavior.

Coordination Cage-Based Emulsifiers: Templated Formation of Metal Oxide Microcapsules Monitored by In Situ LC-TEM.

Metallo‐supramolecular self‐assembly has yielded a plethora of discrete nanosystems, many of which show competence in capturing guests and catalyzing chemical reactions. However, the potential of low‐molecular bottom‐up self‐assemblies in the development of structured inorganic materials has rarely been methodically explored so far. Herein, we present a new type of metallo‐supramolecular surfactant with the ability to stabilize non‐aqueous emulsions for a significant period. The molecular design of the surfactant is based on a heteroleptic coordination cage (CGA‐3; CGA=Cage‐based Gemini Amphiphile), assembled from two pairs of organic building blocks, grouped around two Pd(II) cations. Shape‐complementarity between the differently functionalized components generates discrete amphiphiles with a tailor‐made polarity profile, able to stabilize non‐aqueous emulsions, such as hexadecane‐in‐DMSO. These emulsions were used as a medium for the synthesis of spherical metal oxide microcapsules (titanium oxide, zirconium oxide, and niobium oxide) from soluble, water‐sensitive alkoxide precursors by allowing a controlled dosage of water to the liquid‐liquid phase boundary. Synthesized materials were analyzed by a combination of electron microscopic techniques. In situ liquid cell transmission electron microscopy (LC‐TEM) was utilized for the first time to visualize the dynamics of the emulsion‐templated formation of hollow inorganic titanium oxide and zirconium oxide microspheres.

Dielectric dynamics and optical behaviour of surfactant free LC/silicone oil based non-aqueous emulsions

ABSTRACT We are presenting the non-aqueous emulsions comprising of liquid crystal 8CB (4′-Octyl-4-biphenylcarbonitrile) and silicone oil in varying ratios (5:95, 10:90, 25:75 and 50:50 wt./wt.%). Emulsions are self-stabilised via dipolar interactions, alignment and anchoring without the use of any surfactant. The formation of distinct defects geometries over the studied concentration range of silicone oil in the liquid crystal matrix has been discussed. The dielectric dynamics of the non-aqueous emulsions have been studied in the smectic (30°C) and nematic (38°C) phases over the continuous broadband of frequency 50Hz–1MHz. In both cases (smectic and nematic regions), dielectric permittivity decreases with a rise in the content of the silicone oil in the emulsion systems. The proposed mechanism for such dielectric behaviour has been discussed considering charge/defects boundary interactions and decrement of resultant dipole moment. A relaxation mode in the lower frequency range has been observed for all the emulsion systems. In addition, the emulsion systems have shown significant optical transmission behaviour. A significant enhancement in optical transmission about 82% has been noticed for 25 wt% comparing to 5 wt% emulsion system. Such self-stabilised systems could pave a way to develop dual-frequency LCs systems for progressive technological applications, tunable polarisation filters, and adaptive optics.

Electrically switchable and optically tunable liquid crystal/ silicone oil based non-aqueous emulsions for electro-optical device applications

Liquid crystal/silicone oil based emulsions have been prepared and characterized for interfacial interactions, optical and electro-optical behaviour. Emulsions are stabilized without any surface-active agent via non-covalent interactions, surface alignment and anchoring conditions. Emulsions are characterized by polarizing optical microscopy. Distinct mesomorphic phases, droplet geometries (radial, hedgehog, bipolar) and transitions viz. radial to bipolar and bipolar to broken bipolar are observed as a function of varying silicone oil concentration in liquid crystal. These emulsions are quite stable and show reversible characteristics as a function of time and temperature. The stability of these emulsions has been explained considering hydrophobic interactions, decrease in internal surface tension and anchoring energy etc. Further, the liquid crystal/silicone oil devices have been fabricated and tested for switching and electro-optical behaviour. The emulsion contains 25% silicone oil in liquid crystal matrix shows the best switching characteristics at low deriving voltage 5 V, about 87% enhancement in optical transmission, 8.3 dB contrast and lower Frederiks threshold ~65%. Such switchable and optically tuneable surfactant-free emulsions with controlled morphological dynamics can provide a new door to design novel functional soft material platform for better optical, electro-optical, photonics, sensing and liquid crystals elastomer applications. • Surfactant-free, electrically switchable and optical tuneable liquid crystals/silicone oil emulsions. • 87% enhancement in transmission, 8.3 dB contrast and lower Fredrick's threshold ~65% has been achieved in emulsion systems. • Tuning of optical and electro-optical parameters depends on the boundary conditions, topological deformations.

Synergistic improvement of mechanical and thermal properties in epoxy composites via polyimide microspheres

AbstractAchieving synergetic improvements of mechanical strength, toughness, and thermal stability of epoxy resin has been a crucial but very challenging issue. Herein, to explore a new solution for circumventing this issue, polyimide microspheres were successfully prepared through the inverse nonaqueous emulsion process, and the structure, size distribution and morphologies of polyimide (PI) microspheres were comprehensively investigated. Then the PI microspheres were incorporated in epoxy resin matrix to systematically investigate the mechanical and thermal properties of obtained epoxy/PI microspheres composites. It was found that the PI microspheres can not only enhance the mechanical strength of epoxy resin, but also significantly improve the toughness. Specially, the epoxy‐based composites containing 3 wt% PI microspheres exhibit a 47% increase in tensile strength, while the GIC and Charpy impact strength increase by 106% and 200%, respectively. The toughing mechanism of epoxy/PI microspheres composites was discussed. Moreover, the PI microspheres can also endow the epoxy resin with excellent thermal stability and heat resistance. Thus, this work may open a new opportunity to synergistically enhance the mechanical and thermal properties of epoxy‐based composites and may also give some valuable inspiration for the rational design of other high‐performance thermosetting composites.

Synthesis of well-defined diblock copolymer nano-objects by RAFT non-aqueous emulsion polymerization of N-(2-acryloyloxy)ethyl pyrrolidone in non-polar media

RAFT non-aqueous emulsion polymerization of N-(2-acryloyloxy)ethyl pyrrolidone in n-dodecane using a poly(stearyl methacrylate) precursor is used to prepare sterically-stabilized nanoparticles, which are evaluated as a putative Pickering emulsifier.

Advances and Opportunities of Oil-in-Oil Emulsions

Emulsions are mixtures of two immiscible liquids in which droplets of one are dispersed in a continuous phase of the other. The most common emulsions are oil-water systems, which have found widespread use across a number of industries, for example, in the cosmetic and food industries, and are also of advanced scientific interest. In addition, the past decade has seen a significant increase in both the design and application of nonaqueous emulsions. This has been primarily driven by developments in understanding the mechanism of effective stabilization of oil-in-oil (o/o) systems, either using block copolymers (BCPs) or solid (Pickering) particles with appropriate surface functionality. These systems, as highlighted in this review, have enabled emergent applications in areas such as pharmaceutical delivery, energy storage, and materials design (e.g., polymerization, monolith, and porous polymer synthesis). These o/o emulsions complement traditional emulsions that utilize an aqueous phase and allow the use of materials incompatible with water. We assess recent advances in the preparation and stabilization of o/o emulsions, focusing on the identity of the stabilizer (BCP or particle), the interplay between stabilizer and oils, and highlighting applications and opportunities associated with o/o emulsions.

Antitumoral Drug-Loaded Biocompatible Polymeric Nanoparticles Obtained by Non-Aqueous Emulsion Polymerization.

Non-aqueous dispersions (NAD) with two types of polymeric nanoparticles (NPs), such as hydrophobic poly(ε-caprolactone) (PCL) and hydrophilic cross-linked poly(vinylpyrrolidone) (PNVP), were synthesized in the present study starting from monomer-in-silicone oil (PDMS) polymerizable non-aqueous emulsions stabilized with the same tailor-made PDMS-based block copolymer. These NPs were loaded with CCisplatin, an antitumoral model drug, directly from the emulsion polymerization step, and it was observed that the presence of the drug leads only to a slight increase of the NPs size, from 120 to 150 nm. The drug release kinetics was evaluated at 37 °C in phosphate buffer at pH = 7.4 and it appeared that the drug release rate from the hydrophilic cross-linked PNVP-based NPs is higher than that from the hydrophobic PCL-based NPs. Moreover, haemolysis tests revealed the fact that these two types of NPs have a good compatibility with the blood. Furthermore, for both the free and drug-loaded NPs, the in vitro cytotoxicity and apoptosis was studied on two types of cancer cell lines, such as MCF-7 (breast cancer cell line) and A-375 (skin cancer cell line). Both types of NPs had no cytotoxic effect but, at a concentration of 500 μg/mL, presented an apoptotic effect similar to that of the free drug.

Particle Stabilization of Oil–Fluorocarbon Interfaces and Effects on Multiphase Oil-in-Water Complex Emulsion Morphology and Reconfigurability

Stabilization of oil-oil interfaces is important for nonaqueous emulsions as well as for multiphase oil-in-water emulsions, with relevance to a variety of fields ranging from emulsion polymerization to sensors and optics. Here, we focus on examining the ability of functionalized silica particles to stabilize interfaces between fluorinated oils and other immiscible oils (such as hydrocarbons and silicones) in nonaqueous emulsions and also on the particles' ability to affect the morphology and reconfigurability of complex, biphasic oil-in-water emulsions. We compare the effectiveness of fluorophilic, lipophilic, and bifunctional fluorophilic-lipophilic coated nanoparticles to stabilize these oil-oil interfaces. Sequential bulk emulsification steps by vortex mixing, or emulsification by microfluidics, can be used to create complex droplets in which particles stabilize the oil-oil interfaces and surfactants stabilize the oil-water interfaces. We examine the influence of particles adsorbed at the internal oil-oil interface in complex droplets to hinder the reconfiguration of these complex emulsions upon addition of aqueous surfactants, creating "metastable" droplets that resist changes in morphology. Such metastable droplets can be triggered to reconfigure when heated above their upper critical solution temperature. Thus, not only do these bifunctional silica particles enable the stabilization of a broad array of oil-fluorocarbon nonaqueous emulsions, but the ability to address the oil-oil interface within complex O/O/W droplets expands the diversity of oil chemical choices available and the accessibility of droplet morphologies and sensitivity.

Lipid based non-aqueous nano emulsions: A review

Lipid based non-aqueous nano emulsions: A review

Non-aqueous nanoemulsions as a new strategy for topical application of astaxanthin

The application of astaxanthin is limited by its poor solubility and stability. In the present study, astaxanthin non-aqueous nanoemulsions (ASX-NANE) were developed by high-pressure homogenization method to combine advantages of nanocarriers and non-aqueous emulsions. ASX-NANE had a spherical morphology with a uniformed size distribution and a high entrapment efficiency (98.4 ± 0.3%). The analysis of FTIR indicated that astaxanthin was successfully encapsulated into the lipid core of ASX-NANE. This system was a stable emulsion system over a period of 4 weeks at 25 °C and could protect astaxanthin against degradation. In vitro cell study showed that ASX-NANE had a low toxicity and could protect cells against oxidative stress. In vitro permeation study and skin histological sections revealed the enhanced permeation of astaxanthin and the transformation of stratum corneum with a low systemic absorption and unchanged epidermis. Therefore, non-aqueous nanoemulsions might be an appropriate strategy for the topical application of astaxanthin.