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Dynamic covalent surfactants were designed to prepare pH switchable emulsions. A dynamic covalent bond between nonamphiphilic building blocks (polyethylenimine (PEI) and benzaldehyde (B)) was introduced to form the dynamic covalent surfactant PEI-B. The dynamic nature of covalent bond in PEI-B was confirmed by 1H NMR and fluorescence probe analysis. Stable emulsions were successfully prepared with interfacial active PEI-B at pH 7.8 with various water/paraffin oil ratios under sonication. When lowering the pH to 3.5, a complete phase separation was observed as a result of breaking dynamic covalent bond in the interfacial active PEI-B. After tuning the pH back to 7.8, stable emulsion was obtained again due to the reformation of the dynamic covalent bond and hence interfacial active PEI-B. The emulsification and demulsification were dependent on the formation and breaking of dynamic covalent bond in PEI-B. Such pH-triggered emulsification and demulsification can be switched at least three times. Application of dynamic covalent surfactants will open up a novel route for preparing responsive emulsions. [ABSTRACT FROM AUTHOR]

A new method for generating nanobubbles via microwave irradiation was verified and quantified. AFM measurement showed that nanobubbles with diameters ranging from 200 to 600 nm were generated at a water-HOPG surface by applying microwave radiation to aqueous solutions with 9.0-30.0 mg/L dissolved oxygen. Graphite displays strong microwave absorption and transmits high thermal energy to the surface. Because of the high dielectric constant (20 °C, 80 F/m) and dielectric loss factor, water molecules have a strong ability to absorb microwave radiation. The thermal and nonthermal effects of microwave radiation made contributions to decreasing the gas solubility, thus facilitating nanobubble nucleation. The yield of nanobubbles increased about 10-fold when the irradiation time increased from 60 to 120 s at 200 W of microwave radiation. The nanobubble density increased from 0.8 to 15 μm-2 by improving the working power from 200 to 600 W. An apparent improvement in nanobubbles yield was obtained between 300 and 400 W, and the resulting temperature was 34-52 °C. When the initial dissolved oxygen increased from 11.3 to 30.0 mg/L, the density of nanobubbles increased from 1.2 to 13 μm-2. The generation of nanobubbles could be well controlled by adjusting the gas concentration, microwave power, or irradiation time. The method may be valuable in preparing surface nanobubbles quickly and conveniently for various applications, such as catalysis, hypoxia/anoxia remediation, and templates for preparing nanoscale materials. [ABSTRACT FROM AUTHOR]

Multilayer films of Co–Al layered double hydroxide nanosheets (Co–Al LDH-NS) and graphene oxide (GO) were fabricated through layer-by-layer (LBL) assembly. By using a three-electrode system, the electrochemical performances of the films were investigated to evaluate their potential as electrode materials to be used in flexible supercapacitor devices. The Co–Al LDH-NS/GO multilayer films exhibited a high specific capacitance of 880 F/g and area capacitance of 70 F/m2under the scan rate of 5 mV/s. And the film exhibited good cycle stability over 2000 cycles. After treating the films at 200 °C in H2atmosphere, the specific capacitance and area capacitance were largely increased up to 1204 F/g and 90 F/m2due to partial reduction of GO. A flexible electrode by depositing Co–Al LDH-NS/GO multilayer film onto PET substrate was prepared to show the potential of Co–Al LDH-NS/GO films for flexible energy storage. [ABSTRACT FROM AUTHOR]

Multilayers of manganese(III) porphyrin-linked poly(vinylpyridinium) (MnTMPyP-PVPMe) polyelectrolyte and poly(styrenesulfonic acid-o-maleic) acid (PSS) have been assembled on gold, quartz, and indium tin oxide surfaces by a layer-by-layer (LBL) technique. The assembly process was monitored by measuring their absorption spectra and frequency change after each assembly, both of which confirmed the formation of three-dimensional MnTMPyP-PVPMe/PSS multilayers. The Soret absorption band of porphyrin red shifted about 8 nm in the multilayer compared with that in the dilute aqueous solution. The average mass changes for each assembly of MnTMPyP-PVPMe and PSS were estimated to be about 2.9 and 0.25 μg/cm2, respectively. X-ray photoelectron spectra revealed that the as-prepared multilayers were composed of S 2p , C 1s , N 1s , O 1s, and Mn 2p , corresponding to polymers of MnTMPyP-PVPMe and PSS. A rough surface was observed after the assembly of MnTMPyP-PVPMe on the gold surface, but it became smoother when the PSS layer was adsorbed. The significant difference in the mass change and film morphology after the assembly of MnTMPyP-PVPMe compared to those after the assembly of PSS was ascribed to the reason that the MnTMPyP-PVPMe polyelectrolyte contained large metalloporphyrin macrocycles, which were axially coordinated to the pyridyl substituents of the PVP polymeric backbones. The cyclic voltammograms revealed two couples of redox waves in the phosphate electrolyte solution at pH 11, which corresponded to the electron-transfer processes of Mn(II)/Mn(III) and Mn(III)/Mn(IV) of polymeric manganese porphyrin MnTMPyP-PVPMe. The charge-transfer process was also investigated. Finally, the present MnTMPyP-PVPMe/PSS multilayers were used as a heterogeneous catalyst for the decoloration of an azo dye. [ABSTRACT FROM AUTHOR]

In this letter, we report on the one-step synthesis of Ag@poly(m-phenylenediamine) core−shell nanoparticles (APCSNPs), carried out by direct mixing of aqueous silver nitrate and m-phenylenediamine solutions at room temperature. We further demonstrate the use of APCSNP as a novel fluorescent sensing platform for nucleic acid detection. In this regard, the detection of DNA is accomplished in two steps. First, APCSNP absorbs and quenches the fluorescence of dye-labeled single-stranded DNA (ssDNA) as a probe. Second, hybridizing of the probe with its target produces a double-stranded DNA (dsDNA) that detaches from APCSNP, resulting in the recovery of dye fluorescence. It suggests that this sensing system has a high selectivity down to single-base mismatch, and the results exhibit good reproducibility. Furthermore, we also demonstrate its application for the multiplex detection of nucleic acid sequences. [ABSTRACT FROM AUTHOR]

Purification is a necessary step before the application of nanocrystals (NCs), since the excess matter in nanoparticles solution usually causes a disadvantage to their subsequent coupling or assembling with other materials. In this work, a novel salts-based precipitation technique is originally developed for the precipitation and size-selective precipitation of aqueous NCs. Simply by addition of salts, NCs can be precipitated from the solution. After decantation of the supernatant solution, the precipitates can be dispersed in water again. By means of adjusting the addition amount of salt, size-selective precipitation of aqueous NCs can be achieved. Namely, the NCs with large size are precipitated preferentially, leaving small NCs in solution. Compared with the traditional nonsolvents-based precipitation technique, the current one is simpler and more rapid due to the avoidance of condensation and heating manipulations used in the traditional precipitation process. Moreover, the salts-based precipitation technique was generally available for the precipitation of aqueous nanoparticles, no matter if there were semiconductor NCs or metal nanoparticles. Simultaneously, the cost of the current method is also much lower than that of the traditional nonsolvents-based precipitation technique, making it applicable for mass purification of aqueous NCs. [ABSTRACT FROM AUTHOR]

Three different polymorphic crystalline structures, including microbelts and flowerlike supernanostructures, were obtained via a simple solution process by utilizing different solvents from an oligoarene derivative. Explosive chemosensors based on these self-assembled organic crystalline nanostructures were successfully fabricated. The differences in the structures on the microscopic level and in the film morphologies led to dramatic enhancements of the explosive detection speed. With the evolution of structures from the netted 1D microbelts to the flowerlike supernanostructures, the detection speed of the chemosensors for DNT and TNT was improved by more than 700 times. Our discovery demonstrates that the morphology control through self-assembly provides a new platform to utilize organic crystalline microstructures for chemosensors, optoelectronics, biosensors and bioelectronics, and so forth. [ABSTRACT FROM AUTHOR]