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.

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.

Complex Emulsions by Extracting Water from Homogeneous Solutions Comprised of Aqueous Three-Phase Systems.

Multiple emulsions can be obtained by binary and ternary liquid phase separation. And the use of the aqueous two-phase system provides a simple route to prepare water-in-water-in-oil (W/W/O) or water-in-water-in-water (W/W/W) multiple emulsions. It is thus expected that we can fabricate more complex emulsions by using an aqueous three-phase system. Herein, we present a simple and versatile method to generate complex emulsions based on phase separation in homogeneous droplets made up of aqueous three-phase system: poly(ethylene glycol) (PEG), poly(vinyl alcohol) (PVA) and dextran (DEX) through extracting water from droplets. We examine the formation process and the effect of mass ratio of each two components in the three phase system. Emulsion droplets with five types of morphologies, i.e., binary-core/shell, core/shell-single phase Janus, ellipsoid Janus, multicore-in-matrix and single core-double shell morphologies can be formed, depending on the mass ratio of each two components and modification of PEG with Fe3O4 nanoparticles. We observe transition of core/shell-single phase Janus to binary-core/shell and single core-double shell to core/shell-single phase Janus geometry with prolongation of extracting time, and obtain the geometry map for the formation of different shaped droplets. Due to different affinities of PEG, PVA and DEX to certain materials, we functionalize each compartment in the complex emulsion droplets, and apply the resulting droplet for glucose sensing and the construction of antibody-mediated targeting drug delivery. This emulsion generation method is simple and the choice for the component of the aqueous three-phase system is broad, which can be further extended to generate complex emulsions from aqueous multiphase systems.

Investigation on efficient adsorption of cationic dyes on porous magnetic polyacrylamide microspheres.

We report here the preparation of porous magnetic polyacrylamide microspheres for efficient removal of cationic dyes by a simple polymerization-induced phase separation method. Characterizations by various techniques indicate that the microspheres show porous structures and magnetic properties. They can adsorb methylene blue with high efficiency, with adsorption capacity increasing from 263 to 1977 mg/g as the initial concentration increases from 5 to 300 mg/L. Complete removal of methylene blue can be obtained even at very low concentrations. The equilibrium data is well described by the Langmuir isotherm models, exhibiting a maximum adsorption capacity of 1990 mg/g. The adsorption capacity increases with increasing initial pH and reaches a maximum at pH 8, revealing an electrostatic interaction between the microspheres and the methylene blue molecules. The microspheres also show high adsorption capacities for neutral red and gentian violet of 1937 and 1850 mg/g, respectively, as well as high efficiency in adsorption of mixed-dye solutions. The dye-adsorbed magnetic polyacrylamide microspheres can be easily desorbed, and can be repeatedly used for at least 6 cycles without losing the adsorption capacity. The adsorption capacity and efficiency of the microspheres are much higher than those of reported adsorbents, which exhibits potential practical application in removing cationic dyes.

Versatile preparation of nonspherical multiple hydrogel core PAM/PEG emulsions and hierarchical hydrogel microarchitectures.

The preparation of nonspherical materials composed of separated multicomponents by droplet-based microfluidics remains a challenge. Based on polymerization-induced phase separation and droplet coalescence in microfluidics, we prepared emulsions of variously shaped PAM/PEG core/shell droplets and hydrogels composed of two separated components, which show flexible and transformable hierarchical structures and microarchitectures. We find that AM/PEG aqueous droplets form a core/shell structure after polymerization resulting from phase separation. Thus multicore/shell droplets are easily produced by coalescence of core/shell structures. By changing the polymerization temperature and the flow rate, the morphology of the multicore droplets and the hydrogel can be easily adjusted. The hydrogels exhibit apparent anisotropy and different protein release rates depending on their structures. The preparation technique is simple and versatile and the resulting hydrogels have potential applications in many fields.

Preparation of zeolite-A/chitosan hybrid composites and their bioactivities and antimicrobial activities.

Zeolite-A/chitosan hybrid composites with zeolite contents of 20-55 wt.% were prepared by in situ transformation of silica/chitosan mixtures in a sodium aluminate alkaline solution through impregnation-gelation-hydrothermal synthesis. The products were characterized by X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, scanning electron microscopy, thermogravimetric analysis, and mercury penetration porosimetry. Their in vitro bioactivities were examined using as-synthesized and Ca(2+)-exchanged hybrid composites in simulated body fluid (SBF) for hydroxyapatite (HAP) growth. Their antimicrobial activities for Escherichia coli (E. coli) in trypticase soy broth (TSB) were evaluated using Ag(+)-exchanged hybrid composites. The zeolite-A/chitosan hybrid composites could be prepared as various shapes, including cylinders, plates and thin films. They possessed macropores with pore sizes ranging from 100 to 300 µm and showed compressive mechanical strength as high as 3.2 MPa when the zeolite content was 35 wt.%. Fast growth on the Ca(2+)-exchanged hybrid composites was observed with the highest weight gain of 51.4% in 30 days. The 35 wt.% Ag(+)-exchanged hybrid composite showed the highest antimicrobial activity, which could reduce the 9×10(6) CFU mL(-1)E. coli concentration to zero within 4h of incubation time with the Ag(+)-exchanged hybrid composite amount of 0.4 g L(-1). The bioactivity and antimicrobial activity could be combined by ion-exchanging the composites first with Ca(2+) and then with Ag(+). These zeolite-A/chitosan hybrid composites have potential applications on tissue engineering and antimicrobial food packaging.

Hydrothermal synthesis of pencil-like SAPO-5 and observation of its reversed crystal-growth process.

SAPO-5 with a novel hexagonal pencil-like morphology was hydrothermally synthesized from hydrogels that contain triethylamine and high concentrations of acetic acid at 180 °C for 48 h. The effect of the acetic acid concentration was examined and indicated that usage of a high concentration of acetic acid is crucial to the synthesis of SAPO-5 with a pencil-like morphology. The time-dependent growth process of novel SAPO-5 was observed by scanning electron microscopy with the aid of acid treatment to remove the amorphous materials for clearer observation. The samples were also characterized by X-ray diffraction and Fourier-transform infrared spectroscopy. The results show that the crystal growth at the early stage follows the reversed crystal-growth route. First, the crystallization occurs on the surface of the aggregated amorphous ellipsoidal particles to form a hexagonal prism crystal shell with the encapsulation of amorphous materials. Then, the amorphous materials wrapped inside start to grow to a hexagonal prism inside the hollow larger hexagonal prism shell. Finally, the interior hexagonal prism continues to grow to the two ends with its length beyond that of the larger one by means of the Ostwald ripening process, thus forming the pencil-like crystal.

Combinatorial synthesis of SAPO-34 via vapor-phase transport.

By applying a combinatorial method, SAPO-34 was successfully synthesized via vapor-phase transport technique, and the synthesis factors were systematically examined.