Amphiphilic titania Janus nanoparticles containing ionic groups prepared in oil-water Pickering emulsion

Titania nanoparticles with a diameter of 8 nm underwent an anisotropic modification using apolar 6-bromohexylphosphonic acid and cationic polar N,N,N-trimethyl-6-phosphonohexan-1-aminium bromide. The Janus modification was achieved through a straightforward one-step Pickering emulsion approach using toluene-water mixtures. The resulting Janus particles were compared with isotropically and statistically modified titania particles, where either a single coupling agent is attached to the surface or both coupling agents are assembled over the surface randomly, respectively. The covalent binding of the phosphonic acids to the titania surface was confirmed by FTIR and 31P solid-state CP-MAS NMR analyses. The grafting density was assessed using TGA, elemental analysis, and ICP-MS, revealing grafting densities of 0.1 mmol g-1 to 0.5 mmol g-1 for the cationic coupling agent and 1.2 mmol g-1 to 1.5 mmol g-1 for the apolar coupling agent, respectively. ζ-Potential titration measurements of both pristine and modified particles revealed isoelectric points at pH 4.5 to 9.3, depending on the type of modification. The ability of the particles to stabilize Pickering emulsions was tested under various conditions, with statistically and Janus-modified particles demonstrating a significant increase in stabilization compared to their isotropically modified counterparts. Furthermore, Janus particles were deposited onto glass substrates by a simple layer-by-layer approach. Through the self-assembly of these Janus particles, the glass substrate's properties could be tailored from hydrophilic to hydrophobic to hydrophilic, depending on the dipping cycle.

Ultralight, Robust, Thermal Insulating Silica Nanolace Aerogels Derived from Pickering Emulsion Templates

Synthesis of silica aerogel insulators with ultralight weight and strong mechanical properties using a simplified technique remains challenging for functional soft materials. This study introduces a promising method for the fabrication of mechanically reinforced ultralight silica aerogels by employing attractive silica nanolace (ASNLs)-armored Pickering emulsion templates. For this, silica nanolaces (SiNLs) are fabricated by surrounding a cellulose nanofiber with necklace-shaped silica nanospheres. In order to achieve amphiphilicity, which is crucial for the stabilization of oil-in-water Pickering emulsions, hydrophobic alkyl chains and hydrophilic amine groups are grafted onto the surface of SiNLs by silica coupling reactions. Freeze-drying of ASNLs-armored Pickering emulsions has established a new type of aerogel system. The ASNLs-supported mesoporous aerogel shows 3-fold greater compressive strength, 4-fold reduced heat transfer, and a swift heat dissipation profile compared to that of the bare ASNL aerogel. Additionally, the ASNL aerogel achieves an ultralow density of 8 mg cm-3, attributed to the pore architecture generated from closely jammed emulsion drops. These results show the potential of the ASNL aerogel system, which is ultralight, mechanically stable, and thermally insulating and could be used in building services, energy-saving technologies, and the aerospace industry.

Hydrophobically modified silica nanolaces-armored water-in-oil pickering emulsions with enhanced interfacial attachment energy

HYPOTHESIS

Anisotropic particles with a high aspect ratio led to favorable interfacial adhesion, thus enabling Pickering emulsion stabilization. Herein, we hypothesized that pearl necklace-shaped colloid particles would play a key role in stabilizing water-in-silicone oil (W/S) emulsions by taking advantage of their enhanced interfacial attachment energy.

EXPERIMENTS

We fabricated hydrophobically modified silica nanolaces (SiNLs) by depositing silica onto bacterial cellulose nanofibril templates and subsequently grafting alkyl chains with tuned amounts and chain lengths onto the nanograins comprising the SiNLs.

FINDINGS

The SiNLs, of which nanograin has the same dimension and surface chemistry as the silica nanospheres (SiNSs), showed more favorable wettability than SiNSs at the W/S interface, which was supported by the approximately 50 times higher attachment energy theoretically calculated using the hit-and-miss Monte Carlo method. The SiNLs with longer alkyl chains from C6 to C18 more effectively assembled at the W/S interface to produce a fibrillary interfacial membrane with a 10 times higher interfacial modulus, preventing water droplets from coalescing and improving the sedimentation stability and bulk viscoelasticity. These results demonstrate that the SiNLs acted as a promising colloidal surfactant for W/S Pickering emulsion stabilization, thereby allowing the exploration of diverse pharmaceutical and cosmetic formulations.

Microfluidic macroemulsion stabilization through in situ interfacial coacervation of associative nanoplatelets and polyelectrolytes

HYPOTHESIS

Since macroemulsions tend to break down to lower free energy, they hardly retain their initial drop state. Therefore, studies are being conducted to overcome this based on advanced interface engineering techniques, but it is still challenging. Herein we hypothesize that the stability of giant droplets can be secured without chemical bonding through the interfacial coacervation of polyelectrolyte and associative nanoplatelets.

EXPERIMENTS

We synthesized associative silica nanoplates (ASNPs) via polypeptide-templated silicification and consecutive wettability adjustment. To produce monodisperse macrodroplets, the inner fluid containing partially positively charged ASNPs and the outer fluid dissolving negatively charged polyacrylic acid (PAA) were coflowed through a capillary-based microfluidic channel.

FINDINGS

Dynamic interfacial tension and interfacial rheology measurements revealed that the migration of ASNPs and PAA from each phase to the interface led to the formation of a complex bilayered thin membrane with an enhanced interfacial modulus. In addition, we demonstrated that adjusting the surface properties of ASNPs by coupling a fluorochemical enabled the production of monodisperse fluorocarbon-in-oil-in-water double macroemulsions. These results highlighted the applicability of our microfluidics-based interfacial coacervation technology in the development of complex fluid products with visual differentiation and drug encapsulation.

Preparation of Barium-Hexaferrite/Gold Janus Nanoplatelets Using the Pickering Emulsion Method

Janus particles, which have two surfaces exhibiting different properties, are promising candidates for various applications. For example, magneto-optic Janus particles could be used for in-vivo cancer imaging, drug delivery, and photothermal therapy. The preparation of such materials on a relatively large scale is challenging, especially if the Janus structure consists of a hard magnetic material like barium hexaferrite nanoplatelets. The focus of this study was to adopt the known Pickering emulsion, i.e., Granick's method, for the preparation of barium-hexaferrite/gold Janus nanoplatelets. The wax-in-water Pickering emulsions were stabilized with a combination of cetyltrimethyl ammonium bromide and barium hexaferrite nanoplatelets at 80 °C. Colloidosomes of solidified wax covered with the barium hexaferrite nanoplatelets formed after cooling the Pickering emulsions to room temperature. The formation and microstructure of the colloidosomes were thoroughly studied by optical and scanning electron microscopy. The process was optimized by various processing parameters, such as the composition of the emulsion system and the speed and time of emulsification. The colloidosomes with the highest surface coverage were used to prepare the Janus nanoplatelets by decorating the exposed surfaces of the barium hexaferrite nanoplatelets with gold nanospheres using mercaptan chemistry. Transmission electron microscopy was used to inspect the barium-hexaferrite/gold Janus nanoplatelets that were prepared for the first time.

Stalagmites in karst cave inspired construction: lotus root-type adsorbent with porous surface derived from CO2-in-water Pickering emulsion for selective and ultrafast uranium extraction

Simultaneous construction of porous and hollow adsorbent, especially from gas-in-water Pickering emulsion (PE) reactor, is vital for improving mass transfer kinetics and uptake amount. Inspired by the formation process of stalagmites in karst cave, amino and amidoxime bifunctionalized lotus root-type microsphere with porous surface (NH₂@AO-PLRMS) is prepared by the silica nanoparticles (SPs)-stabilized CO₂-in-water Pickering emulsion reactor and subsequent two-step grafting polymerization. The important roles of SPs acting as Pickering emulsifier, surface pore-forming agent, and adjusting internal lotus root structure are confirmed. Lotus root-type pores are dependent on the interface intensity and the permeability for compressed CO₂ bubbles in PE droplets. Benefitting from the lotus root-type structure and abundant affinity sites, the maximum uranium adsorption capacity of NH₂@AO-PLRMS is 1214.5 mg·g^-1 at 298 k, and an ultrafast uptake process can be achieved in the first 30 min. Both thermodynamic and kinetic studies indicate a spontaneous, entropy increased, and exothermic chemisorption process, and the synergies of amidoxime and amino groups can enhance the adsorption selectivity. Remarkably, NH₂@AO-PLRMS displays a high uranium adsorption capacity and desorption efficiency after seven cycles. These findings provide a way to obtain adsorbents with enhanced uranium extraction performance from gas-in-water PE reactor.

Size-Controlled Formation of Polymer Janus Discs

A straightforward method is presented for the preparation of nano- to micrometer-sized Janus discs with controlled shape, size, and aspect ratio. The method relies on cross-linkable ABC triblock terpolymers and involves first the preparation of prolate ellipsoidal microparticles by combining Shirasu porous glass (SPG) membrane emulsification with evaporation-induced confinement assembly (EICA). By varying the pore diameter of the SPG membrane, we produce Janus discs with controlled size distributions centered around hundreds of nanometers to several microns. We further transferred the discs to water by mild sulfonation of PS to polystyrene sulfonic acid (PSS) and verified the Janus character by subsequent labelling with cationic nanoparticles. Finally, we show that the sulfonated Janus discs are amphiphilic and can be used as efficient colloidal stabilizers for oil-in-water (O/W) emulsions.

Microfluidic production of monodisperse emulsions for cosmetics

Droplet-based microfluidic technology has enabled the production of emulsions with high monodispersity in sizes ranging from a few to hundreds of micrometers. Taking advantage of this technology, attempts to generate monodisperse emulsion drops with high drug loading capacity, ordered interfacial structure, and multi-functionality have been made in the cosmetics industry. In this article, we introduce the practicality of the droplet-based microfluidic approach to the cosmetic industry in terms of innovation in productivity and marketability. Furthermore, we summarize some recent advances in the production of emulsion drops with enhanced mechanical interfacial stability. Finally, we discuss the future prospects of microfluidic technology in accordance with consumers' needs and industrial attributes.

Energetically Preferred Bilayered Coacervation of Oppositely Charged ZrHP Nanoplatelets

A platform is introduced for bilayered coacervation of oppositely charged nanoplatelets (NPLs) at the oil-water interface. To this end, we synthesized two types of zirconium hydrogen phosphate (ZrHP) NPLs, cationically charged NPLs (CNPLs), and anionically charged NPLs (ANPLs) by conducting surface-initiated atom transfer radical polymerization. Taking advantage of the platelet geometry and controlled wettability, we demonstrated that ANPLs and CNPLs coacervate themselves to form a bilayered NPL membrane at the interface, which was directly confirmed by confocal laser scanning microscopy. Via theoretical consideration using the hit-and-miss Monte Carlo method, we determined that electrostatic attraction-driven coacervation of ANPLs and CNPLs at the interface shows a minimum attachment energy of ∼ -10⁶ k_BT, which is comparable to the cases where NPLs charged with the same type of ions are attached. Finally, this unique and novel interfacial coacervation behavior allowed us to develop a pH-responsive smart Pickering emulsion system.