Triple-Responsive Pickering Emulsion Stabilized by Core Cross-linked Supramolecular Polymer Particles

Bioinspired superwetting oil-water separation strategy: toward the era of openness

Bioinspired superwetting oil-water separation strategies have received significant attention for their potential in addressing global water scarcity and aquatic pollution challenges. Over the past two decades, the field has rapidly developed, reaching a pivotal phase of innovation in the oil-water separation process. However, many groundbreaking studies have not received extensive scientific recognition. In this review, we systematically examine the application of bioinspired superwetting materials for complex multiscale oil-water separation. We discuss the development of 2D membrane filtration and 3D sponge adsorption materials in confined spaces, summarizing the core separation mechanisms, key research findings, and the evolutionary logic of these materials. Additionally, we highlight emerging open-space separation strategies, emphasizing several novel dynamic separation devices of significant importance. We evaluate and compare the design concepts, separation principles, materials used, comprehensive performance, and existing challenges of these diverse strategies. Finally, we summarize these advantages, critical bottlenecks, and prospects of this field and propose potential solutions for real oil-water separation processes from a general perspective.

Reversible Emulsions from Polyoxometalate-Polymer: A Robust Strategy to Cyclic Emulsion Catalysis and High-Internal-Phase Emulsion Materials

Reversible Pickering emulsions, achieved by switchable, interfacially active colloidal particles, that enable on-demand emulsification/demulsification or phase inversion, hold substantial promise for biphasic catalysis, emulsion polymerization, cutting fluids, and crude oil pipeline transportation. However, particles with such a responsive behavior usually require complex chemical syntheses and surface modifications, limiting their extensive use. Herein, we report a simple route to generate emulsions that can be controlled and reversibly undergo phase inversion. The emulsions are prepared and stabilized by the interfacial assembly of polyoxometalate (POM)-polymer, where their electrostatic interaction at the interface is dynamic. The wettability of the POMs that dictates the emulsion type can be readily regulated by tuning the number of polymer chains bound to POMs, which, in turn, can be controlled by varying the concentrations of both components and the water/oil ratio. In addition, the number of polymer chains anchored to the POMs can be varied by controlling the number of negative charges on the POMs through an in situ redox reaction. As such, a reversible inversion of the emulsions can be triggered by switching between exposure to ultraviolet light and the introduction of oxygen. Combining the functions of POM itself, a cyclic interfacial catalysis system was realized. Inversion of the emulsion also affords a pathway to high-internal-phase emulsions. The diversity of the POMs, the polymers, and the responsive switching groups open numerous new, simple strategies for designing a wide range of responsive soft matter for cargo loading, controlled release, and delivery in biomedical and engineering applications without time-consuming particle syntheses.

Pickering Emulsion Stabilized by β-Cyclodextrin and Cinnamaldehyde/β-Cyclodextrin Composite

A Pickering emulsion was prepared using β-cyclodextrin (β-CD) and a cinnamaldehyde (CA)/β-CD composite as emulsifiers and corn oil, camellia oil, lard oil, and fish oil as oil phases. It was confirmed that Pickering emulsions prepared with β-CD and CA/β-CD had good storage stability. The rheological experiments showed that all emulsions had G' values higher than G″, thus confirming their gel properties. The results of temperature scanning rheology experiments revealed that the Pickering emulsion prepared with β-CD and CA/β-CD composites had high stability, in the range of 20-65 °C. The chewing properties of Pickering emulsions prepared by β-CD and corn oil, camellia oil, lard, and herring oil were 8.02 ± 0.24 N, 7.94 ± 0.16 N, 36.41 ± 1.25 N, and 5.17 ± 0.13 N, respectively. The chewing properties of Pickering emulsions made with the CA/β-CD composite and corn oil, camellia oil, lard, and herring oil were 2.51 ± 0.05 N, 2.56 ± 0.05 N, 22.67 ± 1.70 N, 3.83 ± 0.29 N, respectively. The texture properties confirmed that the CA/β-CD-composite-stabilized-emulsion had superior palatability. After 28 days at 50 °C, malondialdehyde (MDA) was detected in the emulsion. Compared with the β-CD and CA + β-CD emulsion, the CA/β-CD composite emulsion had the lowest content of MDA (182.23 ± 8.93 nmol/kg). The in vitro digestion results showed that the free fatty acid (FFA) release rates of the CA/β-CD composite emulsion (87.49 ± 3.40%) were higher than those of the β-CD emulsion (74.32 ± 2.11%). This strategy provides ideas for expanding the application range of emulsifier particles and developing food-grade Pickering emulsions with antioxidant capacity.

Amphiphilic Lignin Nanoparticles Made from Lignin-Acrylic Acid-Methyl Methacrylate Copolymers

In this study, a novel amphiphilic KL-AA-MMA nanoparticle was prepared through the graft copolymerization of kraft lignin (KL) with acrylic acid (AA) and methyl methacrylate (MMA), using potassium persulfate as an initiator in a water/dimethyl sulfoxide solvent medium, which was followed by the nanoprecipitation technique using dimethylformamide as a solvent and deionized water as an antisolvent. The successful graft polymerization was verified by ¹H-nuclear magnetic resonance (NMR), ³¹P-NMR, and Fourier transform infrared (FTIR) analyses; and the grafting yield of the generated KL-AA-MMA copolymer ranged from 68.2% to 96.5%. Transmission electron microscopy (TEM) observation revealed the formation of amorphous KL-AA-MMA nanoparticles. Additionally, KL-AA-MMA9 nanoparticles with the highest yield exhibited the minimum hydrodynamic diameter and polydispersity of 261 nm and 0.153, respectively. Moreover, the amphiphilicity of KL-AA-MMA nanoparticles was significantly improved by the grafting of MMA monomers. Finally, the adsorption performance of KL-AA-MMA nanoparticles at the xylene interface was evaluated by a quartz crystal microbalance with dissipation (QCM-D). The results demonstrated that the most amphiphilic sample, KL-AA-MMA9 nanoparticles, with the smallest hydrodynamic size displayed the highest adsorption on the oil/water interface. This product provides a wide range of applications in oil/water emulsions.

Recent Progress toward Physical Stimuli-Responsive Emulsions

Emulsion as a fine dispersion of immiscible liquids has involved widespread applications in industry, pharmaceuticals, agriculture and personal care. Stimuli-responsive emulsions capable of on-demand demulsification or changing their properties are required in many cases such as controllable release cargo, oil recovery, emulsifiers recycle and product separation, great progress has been achieved in these areas. Among these various triggers, much effort has been made to develop physical stimuli, due to the noninvasive and environmentally friendly characteristics. Physical stimuli-responsive emulsions provide a plenty of valuable practical applications in the fields of sustainable industry, biomedical reaction, drug delivery. Here, we summarize the recent development in the field of emulsions in response to physical stimuli consisting of temperature, light, magnetic field, electrical field, etc. The preparation methods and mechanisms of physical stimuli-responsive emulsions and their applications of catalysis reaction, drug delivery, and oil recovery are highlighted in this review. The future directions and outstanding problems of the physical stimuli-responsive emulsions are also discussed. This article is protected by copyright. All rights reserved.

Polymeric nanostructures based on azobenzene and their biomedical applications: synthesis, self-assembly and stimuli-responsiveness

Amphiphilic polymers can self-assemble to form nanoparticles with different structures under suitable conditions. Polymer nanoparticles functionalized with aromatic azo groups are endowed with photo-responsive properties. In recent years, a variety of photoresponsive polymers and nanoparticles have been developed based on azobenzene, using different molecular design strategies and synthetic routes. This article reviews the progress of this rapidly developing research field, focusing on the structure, synthesis, assembly and response of photo-responsive polymer assemblies. According to the molecular structure, photo-responsive polymers can be divided into linear polymers containing azobenzene in a side chain, linear polymers containing azobenzene in the main chain, linear polymers containing azobenzene in an end group, branched polymers containing azobenzene and supramolecular polymers containing azobenzene. These systems have broad biomedical application prospects in the field of drug delivery and imaging applications.

Spatio-temporal control over destabilization of Pickering emulsions stabilized by light-sensitive dextran-based nanoparticles

The implementation of light-sensitive Pickering emulsions with spatio-temporal responsiveness in advanced applications like drug-delivery, colloidal or reaction engineering would open new avenues. However, curiously, light-sensitive Pickering emulsions are barely studied in the literature and their biocompatibility and/or degradability scarcely addressed. Thus, their development remains a major challenge. As an original strategy, we synthesized light-sensitive nanoparticles based on biocompatible Poly(NitroBenzylAcrylate) grafted dextran (Dex-g-PNBA) to stabilize O/W Pickering emulsions. The produced emulsions were stable in time and could undergo time and space-controlled destabilization under light stimulus. Irradiation time and alkaline pH-control of the aqueous phase were proved to be the actual key drivers of destabilization. As the nanoparticles themselves were photolyzed under light stimulus, possible harmful effects linked to accumulation of nanomaterials should be avoided. In addition to UV light (365 nm), visible light (405 nm) was successfully used for the spatio-temporal destabilization of the emulsions, offering perspectives for life science applications.

Pickering/Non-Pickering Emulsions of Nanostructured Sulfonated Lignin Derivatives

Sulfoethylated lignin (SEKL) polymeric surfactant and sulfoethylated lignin nanoparticles (N-SEKL) with a size of 750±50 nm are produced by using a facile green process involving a solvent-free reaction and acidification-based fractionation. SEKL forms a liquid-like conventional emulsion with low viscosity that has temporary stability (5 h) at pH 7. However, N-SEKL forms a gel-like, motionless, and ultra-stable Pickering emulsion through a network of interactions between N-SEKL particles, which creates steric hindrance among the oil droplets at pH 3. The deposition of SEKL and N-SEKL on the oil surface is monitored by a using a quartz crystal microbalance. Experimentally, the formation of emulsions at pH 7 is found to be reversible owing to the low adsorption energy ΔE of SEKL on the oil droplet (ΔE≈15 k_B T), which is determined with the help of three-phase contact-angle measurements. However, the high desorption energy (ΔE≈6.0×10⁵  k_B T) of N-SEKL makes it irreversibly adsorb on the oil droplets. SEKL is too hydrophilic to attach to the oil interface (ΔE≈0) and thus does not facilitate emulsion formation at pH 11. Therefore, it is feasible to apply SEKL for the formulation of Pickering or non-Pickering emulsions in the form of nanoparticles or polymeric surfactants, depending on the targeted application.