Based on the advantages of microfluidics in the field of nanoparticle synthesis, a controllable synthesis method for silver nanoparticles using a double-layer Y-shaped splitting and recombination (SAR) micromixer is proposed. First, the liquid phase synthesis mechanism of silver nanoparticles, the working principle of the double-layer Y-shaped SAR micromixer, and the mixing performance of micromixer at different Reynolds number (Re) are analyzed. Then, the micromixer is used to synthesize silver nanoparticles, and the effects of reductant concentration, polyvinylpyrrolidone (PVP) and inlet flow rate on the size, distribution and morphology of the synthesized silver nanoparticles are investigated comprehensively. The synthesized silver nanoparticles are characterized by UV-spectrometer and transmission electron microscopy (TEM). The experimental results show that the reductant concentration, PVP, and inlet flow rate have a direct impact on the size, distribution, monodispersity and morphology of the synthesized nanoparticles. The moderate reductant concentration makes the size of silver nanoparticles larger and the size uniformity is better. Adding PVP to the experimental reagent can prevent the aggregation of silver nanoparticles, consequently, the synthesized particles have a uniform distribution and a better morphology. The changes in inlet flow rate and Re directly affect the mixing efficiency, which in turn affect the formation of silver atoms and silver nanocrystal nuclei and have a greater impact on particle concentration. The proposed micromixer has excellent mixing performance and can be used in other fields such as controllable synthesis, biomedicine and microchemical systems.
Flexible and thin polymer surfaces with superhydrophobic characteristic have great prospects in many engineering fields, such as self-cleaning, ice-proofing, and drag reduction. However, the large-scale practical applications of superhydrophobic materials are still rarely reported and generally impeded by the existing fabrication methods due to the limits of complicated procedures, toxic solvent applications, harsh conditions occasionally, high cost and low yield. Herein, an ultra-facile one-step debonding method to develop superhydrophobic surface based on multilayer extruded macromolecular PA/PE composite film is developed. By employing thermoplasticity and extensibility of polymer film, the pristine smooth PA/PE film could get hierarchical microscale grass-like, block island and groove structures on its surface, forming an open air-pockets layer, which endows the normal film with new features of superhydrophobicity, low water adhesion, self-cleaning and ice-proofing with inexpensive, environmentally friendly, simple, and fast fabricating strategy.
Combined liquid-phase reduction method and ultrasonic vibration mixing technology, a new method for controllable synthesis of silver nanoparticles (AgNPs) using an acoustofluidic micromixer is proposed. First, the working mechanism of the acoustofluidic micromixer and the basic principle of the liquid-phase reduction method were briefly described. Then, based on the finite element theory, the simulation software COMSOL was utilized to analyze the vibration pattern and acoustic streaming field of the device. Finally, a series of AgNPs synthesis experiments were carried out using a self-made prototype. Controllable synthesis was achieved by adjusting the control parameters of the device and changing the reagent dosage. And the synthesized AgNPs were characterized by UV spectroscopy and transmission electron microscopy (TEM). Simulation and experimental results show that rapid and homogeneous mixing reaction inside a microchannel is demonstrated via the acoustic streaming phenomenon induced by the interdigital transducers (IDT). The driving voltage, reductant, and protectant concentration have significant effects on the synthesis of AgNPs. Ultrasonic vibration combines with a proper protectant dosage can effectively inhibit particle agglomeration and ensure that the synthesized AgNPs have good homogeneity and monodispersity. When the working voltage is 30-40 V and the concentration ratio of reductant to the precursor is 2:1, the quality of the synthesized AgNPs is better. The samples are approximately spherical, without a large number of agglomerates, and high monodispersity. At this point, the average particle size is about 24.4 nm and the deviation is below 5.01 nm. The excellent and fast mixing reaction performance makes the proposed acoustofluidic micromixer a promising candidate for a wide variety of applications.
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