Electrically controlled mass transport into microfluidic droplets from nanodroplet carriers with application in controlled nanoparticle flow synthesis.

Microfluidic droplets have been applied extensively as reaction vessels in a wide variety of chemical and biological applications. Typically, once the droplets are formed in a flow channel, it is a challenge to add new chemicals to the droplets for subsequent reactions in applications involving multiple processing steps. Here, we present a novel and versatile method that employs a high strength alternating electrical field to tunably transfer chemicals into microfluidic droplets using nanodroplets as chemical carriers. We show that the use of both continuous and cyclic burst square wave signals enables extremely sensitive control over the total amount of chemical added and, equally importantly, the rate of addition of the chemical from the nanodroplet carriers to the microfluidic droplets. An a priori theoretical model was developed to model the mass transport process under the convection-controlled scenario and compared with experimental results. We demonstrate an application of this method in the controlled preparation of gold nanoparticles by reducing chloroauric acid pre-loaded in microfluidic droplets with l-ascorbic acid supplied from miniemulsion nanodroplets. Under different field strengths, l-ascorbic acid is supplied in controllable quantities and addition rates, rendering the particle size and size distribution tunable. Finally, this method also enables multistep synthesis by the stepwise supply of miniemulsions containing different chemical species. We highlight this with a first report of a three-step Au-Pd core-shell nanoparticle synthesis under continuous flow conditions.

Functionalized Magnetic Silica Nanoparticles for Highly Efficient Adsorption of Sm3+ from a Dilute Aqueous Solution.

Separation of Sm3+ from a dilute solution via conventional solvent extraction is often plagued by emulsion and third phase formation. These problems can be overcome with functionalized magnetic nanoparticles that can capture the target species and be separated from the raffinae phase rapidly and efficiently on application of a magnetic field. Magentic silica nanoparticles (Fe2O3/SiO2) were synthesized by a modified Stöber method and functionalized with carboxylate (Fe2O3/SiO2/RCOONa) and phosphonate (Fe2O3/SiO2/R1R2PO3Na) groups to achieve high adsorption capacity and fast adsorption kinetics. The adsorbents were characterized by X-ray diffraction analysis, transmission electron microscopy, BET measurements, magnetization property evaluation, Fourier infrared spectroscopy, and thermogravimetric analysis. Equilibrium adsorption of Sm3+ on Fe2O3/SiO2/RCOONa particles was attained within 10 min and within 20 min on Fe2O3/SiO2/R1R2PO3Na nanoparticles. The kinetic data were correlated well with a pseudo-second-order model. Adsorption capacities of Fe2O3/SiO2/RCOONa and Fe2O3/SiO2/R1R2PO3Na were 228 and 180 mg/g, respectively. The recovery of the adsorbed Sm3+ using 2 mol/L HCl as desorption agent was evaluated. The adsorption mechanism is discussed based on FTIR analysis, carboxylate group/Sm3+ molar ratio, phosphonate group/Sm3+ molar ratio, and pH. The adsorbents show significant potential for Sm3+ recovery in industrial applications.

Droplet-Templated Antisolvent Spherical Crystallization of Hydrophilic and Hydrophobic Drugs with an in situ Formed Binder.

This study presents a novel droplet-templated antisolvent spherical crystallization method applicable to both hydrophilic and hydrophobic drugs. In both cases, an alginate hydrogel binder forms in situ, concurrently with the crystallization process, effectively binding the drug crystals into monodisperse spheres. This study presents a detailed process description with mass transfer modeling, and with characterization of the obtained alginate/drug spheres in terms of morphology, composition, and drug loading. Although glycine and carbamazepine are used as model hydrophilic and hydrophobic drugs, this method is easily generalized to other drugs, and offers several benefits such as minimal thermal impact, fast crystallization rates, high drug-binder loading ratios, and high selectivity toward metastable polymorphs.

Droplet microfluidics with a nanoemulsion continuous phase.

We present the first study of a novel, generalizable method that uses a water-in-oil nanoemulsion as the continuous phase to generate uniform aqueous micro-droplets in a capillary-based microfluidic system. We first study the droplet generation mechanism in this system and compare it to the more conventional case where a simple oil/solvent (with surfactant) is used as the continuous phase. Next, we present two versatile methods - adding demulsifying chemicals and heat treatment - to allow active online chemical interaction between the continuous and dispersed phases. These methods allow each generated micro-droplet to act as a well-mixed micro-reactor with walls that are 'permeable' to the nanoemulsion droplets and their contents. Finally, we demonstrate an application of this system in the fabrication of uniform hydrogel (alginate) micro-beads with control over particle properties such as size and swelling. Our work expands the toolbox of droplet-based microfluidics, enabling new opportunities and applications involving active colloidal continuous phases carrying chemical payloads, both in advanced materials synthesis and droplet-based screening and diagnostic methods.

Self-assembled multilayer films of sulfonated graphene and polystyrene-based diazonium salt as photo-cross-linkable supercapacitor electrodes.

Photo-cross-linkable multilayer films composed of sulfonated reduced graphene oxide (SRGO) and polystyrene-based diazonium salt (PSDAS) were fabricated by electrostatic layer-by-layer (LbL) self-assembly. Polystyrene with narrow molecular weight distribution was synthesized by atom transfer radical polymerization (ATRP), and cationic PSDAS was prepared through nitration, reduction, and diazotization reactions. Negatively charged SRGO nanosheets were prepared through prereduced by NaBH4, modified by diazonium salt of sulfanilic acid, and then further reduced by hydrazine. The multilayer films were obtained by alternately dipping substrates in the PSDAS solution and SRGO dispersion in acidic conditions. The cross-linking between the components occurred during the multilayer formation process and was further achieved by the UV light irradiation after the film preparation. The assembling process and surface morphology of LbL multilayer films were monitored by UV-vis spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM). The cross-linking between SRGO and PSDAS was verified by attenuated total reflectance FTIR (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and contact angle measurement. The graphene nanosheets were found to be homogeneously distributed in the cross-linked network of the films. The large accessible surface area of graphene nanosheets and the cross-linking structure afforded the LbL films with high specific capacitance and excellent cyclic stability when used as supercapacitor electrodes. At a sweeping rate of 10 mV/s, the film with nine bilayers exhibited a specific capacitance of 150.4 F/g with ideal rectangular cyclic voltammogram. Large capacitance retention of 97% was observed after 10 000 charge-discharge cycles under the scanning rate of 1000 mV/s. This new approach for preparing graphene-containing multilayer films can be used to develop supercapacitor electrodes and other functional devices.