Magnetic ionic liquid‐water Janus droplets: Preparation, structure and morphology adjustment and magnetic manipulation

Inner Rotation of Pickering Janus Emulsions

Janus droplets were prepared by vortex mixing of three non-mixable liquids, i.e., olive oil, silicone oil and water, in the presence of gold nanoparticles (AuNPs) in the aqueous phase and magnetite nanoparticles (MNPs) in the olive oil. The resulting Pickering emulsions were stabilized by a red-colored AuNP layer at the olive oil/water interface and MNPs at the oil/oil interface. The core-shell droplets can be stimulated by an external magnetic field. Surprisingly, an inner rotation of the silicon droplet is observed when MNPs are fixed at the inner silicon droplet interface. This is the first example of a controlled movement of the inner parts of complex double emulsions by magnetic manipulation via interfacially confined magnetic nanoparticles.

Complex emulsions for shape control based on mass transfer and phase separation

Complex emulsions are used to fabricate new morphologies of multiple Janus droplets, evolving from non-engulfing to complete engulfing core/shell configuration. The produced droplets contain an aqueous phase of dextran (DEX) solution and an oil phase, which is mixed with ethoxylated trimethylolpropane triacrylate (ETPTA) and poly(ethylene glycol) diacrylate (PEGDA). The PEGDA in the oil phase is transferred into the aqueous phase to form complex morphologies due to the phase separation of PEGDA and DEX. The effects are investigated including the ratio of oil to aqueous phase, the content of initial PEGDA, DEX and surfactants, and the type of surfactants. DEX/PEGDA-ETPTA core/shell-single phase Janus droplets are formed with an increasing engulfed oil droplet into the aqueous droplet while the ratio of oil to aqueous phase increases or the initial PEGDA content increases. The high DEX content leads to the DEX-PEGDA-ETPTA doublet Janus. The use of surfactants polyglycerol polyricinoleate (PGPR) and Span 80 results in the formation of DEX/PEGDA/ETPTA single core/double shell and DEX/PEGDA-ETPTA core/shell-single phase Janus droplets, respectively. These complex emulsions are utilized to fabricate solid particles of complex shapes. This method contributes to new material design underpinned by mass transfer and phase separation, which can be extended to other complex emulsion systems.

Preparation of Silica@Silica Core-Shell Microspheres Using an Aqueous Two-Phase System in a Novel Microchannel Device

In the present work, a novel microchannel device was developed and used for the preparation of core-shell microspheres combining with a dextran/poly(ethylene glycol) diacrylate (DEX/PEGDA) aqueous two-phase system. Silica@silica core-shell microspheres were prepared as a model material. Silica@silica core-shell microspheres with different sizes of cores and thicknesses of shells were prepared by using different flowrate ratios of DEX/silica and PEGDA/silica aqueous solutions. The content of colloidal silica and the calcination temperature have a significant effect on the texture properties of the prepared core-shell microspheres. The surface area decreased from 199 to 177 m²/g with an increase in the colloidal silica content from 30 to 60 wt %. For a specific colloidal silica content (50 wt %), with the increase in calcination temperature from room temperature to 650 °C, the total pore volume went through a maximum of 0.7 cm³ g^-1 with a surface area of 178 m² g^-1 and pore size of 7.32 nm at 450 °C. Due to the accumulation of metal nanoparticles in DEX, different metal nanoparticles (Ni and Pd) were successfully introduced into the core of the core-shell microspheres for the preparation of silica/metal nanoparticles@silica core-shell microsphere catalysts. The catalysts showed similar catalytic performance as the metal nanoparticles for hydrogenation of 4-nitrophenol with a conversion higher than 95%. However, the core-shell microsphere catalyst is much easier to recover. The reuse experiments indicated that the core-shell catalyst has high stability.

Fabrication of PAA-PETPTA Janus Microspheres with Respiratory Function for Controlled Release of Guests with Different Sizes

Poly(acrylic acid)-poly(ethoxylated trimethylolpropane triacrylate) (PAA-PETPTA) Janus microspheres with "respiratory" function for controlled release were prepared by polymerization of acrylic acid-ethoxylated trimethylolpropane triacrylate (AA-ETPTA) Janus microdroplets in a continuous oil phase in a simple capillary-based microfluidic device with the assistance of UV radiation. The flow rate ratios of AA and ETPTA phases and surfactant content in the continuous oil phase have a significant effect on the structure of the Janus microspheres. PAA part in the Janus microspheres has respiratory function for loading and release due to the different stimuli responses to different pHs. The hollow structure of PETPTA part with different sizes of opening serves as the host materials for PAA and could control release rate further due to the different opening sizes. The obtained PAA-PETPTA Janus microspheres showed high rhodamine B (RhB) loading of 860 mg g^-1 and different controlled-release behavior in water with different pHs. The release rate increases with the increase of pH and the contact area of PAA part with water. The maximum controlled-release time for RhB was about 3 h in water with pH of 5. In addition, the Janus microspheres also showed controlled-release behavior for larger size guests, e.g., 150 nm polystyrene beads, which indicated a wide range of application. The loading and release behaviors for guests, for instance, for RhB, have almost no change even after six times of reuse, which indicated a high stability.

Janus-Type Gold/Polythiophene Composites Formed via Redox Reaction at the Ionic Liquid|Water Interface

Janus-type Au/polythiophene (PT) composites have been prepared by utilizing the liquid/liquid interface between water (W) and a hydrophobic ionic liquid (IL) as the redox reaction site. AuCl₄^- is reductively deposited, and terthiophene is oxidatively polymerized spacio-selectively at the IL|W interface, leading to the formation of the Au/PT composites. The composites are Janus-type Au-attached PT plates with two surface morphologies, flat surface and flowerlike surface at the W and IL sides of the plates at the IL|W interface, respectively. Not only surface morphologies but also attached Au structures are different at the two surfaces; Au microurchins on the flat surface and dendritic Au nanofibers on the flowerlike surface. Optical and scanning electron microscopic observations have revealed that nanofibers and microurchins are formed at the early and later stage of the reaction, respectively. Electrochemistry at the IL|W interface has illustrated that electron transfer across the IL|W interface during the formation of the Janus-type Au/PT composites is coupled with ion transfer of AuCl₄^- to compensate for the charge unbalance in the two liquid phases. AuCl₄^- transferred into IL is found to be the source of the dendritic Au nanofibers formed at the IL side of the PT plates.