Droplet‐Based Microfluidic Synthesis of Anisotropic Metal Nanocrystals

A droplet‐based microfluidic method for the preparation of anisotropic gold nanocrystal dispersions is presented. Gold nanoparticle seeds and growth reagents are dispensed into monodisperse picoliter droplets within a microchannel. Confinement within small droplets prevents contact between the growing nanocrystals and the microchannel walls. The critical factors in translating macroscale flask‐based methods to a flow‐based microfluidic method are highlighted and approaches are demonstrated to flexibly fine tune nanoparticle shapes into three broad classes: spheres/spheroids, rods, and extended sharp‐edged structures, thus varying the optical resonances in the visible–near‐infrared (NIR) spectral range.     

Self-Driven Droplet Motions Below their Icing Points

Liquid fluidity is a most key prerequisite for a broad range of technologies, from energy, fluid machineries, microfluidic devices, water, and oil transportation to bio-deliveries. While from thermodynamics, the liquid fluidity gradually diminishes as temperature decreases until completely solidified below icing points. Here, self-driven droplet motions are discovered and demonstrated occurring in icing environments and accelerating with both moving distances and droplet volumes. The self-driven motions, including self-depinning and continuous wriggling, require no surface pre-preparation or energy input but are triggered by the overpressure spontaneously established during icing and then continuously accelerated by capillary pulling of frosts. Such self-driven motions are generic to a broad class of liquid types, volumes, and numbers on various micro-nanostructured surfaces and can be facilely manipulated by introducing pressure gradients spontaneously or externally. The discovery and control of self-driven motions below icing points can greatly broaden liquid-related applications in icing environments.     

Performance characteristics of mechanical foam‐breakers fitted to a stirred‐tank reactor

In a stirred‐tank reactor (STR), a comparison of the performance of mechanical foam‐breakers: a six‐blade turbine (F‐B), a six‐blade vaned disk (V‐D), a two‐blade paddle (T‐P), a conical rotor (C‐R), a fluid‐impact dispersion apparatus (FIDA) and a rotating disk mechanical foam‐breaker (MFRD) was carried out using defined foaming media. The foam‐breaking ranges (relative to the gas superficial velocity, U_g) of the T‐P, C‐R and FIDA were inferior to that of the F‐B, V‐D and MFRD. The power consumption, P_kc, for foam‐breaking in the MFRD was the lowest among the F‐B, V‐D and MFRD. Operation of the F‐B and V‐D in the STR caused a considerable amount of liquid droplets from the collapsed foam to be entrained with the exhaust air. © 2002 Society of Chemical Industry     

Heat transfer coefficient for nitrogen droplets film-boiling on a food surface

A method of measuring heat transfer rates from a solid food surface to liquid nitrogen droplets on it has been developed using 0.5 sec repeat-shot photography. Droplet diameters were varied from 0.1 to 2.5 mm and food surface temperatures from +30 to -100°C. All measurements were carried out at atmospheric pressure. The mean heat transfer coefficients were determined using an energy balance for the droplets. An empirical dimensionless correlation equation was established, and the significance of the results for food freezing by liquid nitrogen sprays is critically discussed.     

Gradient Quasi-Liquid Surface Enabled Self-Propulsion of Highly Wetting Liquids

Self-propulsion of highly wetting liquids is important in heat exchanger, air conditioning, and refrigeration systems. However, it is challenging to achieve such a spontaneous motion as these liquids tend to wet all the surfaces due to their ultralow surface tensions. Despite that extensive asymmetric surface structures and gradient chemical coatings are developed for directional droplet transport, they will be flooded and covered by these liquids. Here, this challenge is addressed by creating a gradient quasi-liquid surface to achieve the self-propulsion of droplets with surface tensions down to 10.0 mN m⁻¹. Such a surface engineered by tethering flexible polymers with gradient grafting density shows ultralow contact angle hysteresis (<1^o) to highly wetting liquids. Thus, the surface can simultaneously provide sufficient driving forces through the gradient wettability and negligible retention forces through the slippery boundary lubrication for spontaneous droplet movement. Moreover, continual self-propulsion of tiny droplets is achieved by spraying highly wetting liquids in simulated condensation conditions and demonstrates that adding temperature gradient can further accelerate the self-propulsion. The study provides a new paradigm to promote passive removal of highly wetting droplets, leading to potential impacts in enhancing condensation heat transfer regardless of surface orientations.     

From the nucleation of wiggling Au nanostructures to the dome-shaped Au droplets on GaAs (111)A, (110), (100), and (111)B

In this paper, the systematic evolution process of self-assembled Au droplets is successfully demonstrated on GaAs (111)A, (110), (100), and (111)B. On various GaAs substrates, self-assembled Au clusters begin to nucleate at around 300°C, and then, they develop into wiggly Au nanostructures at 350°C. Between 400°C and 550°C, the self-assembled dome-shaped Au droplets with fine uniformity are fabricated with various sizes and densities based on the Volmer-Weber growth mode. Depending on the annealing temperature, the size including the average height and lateral diameter and the density of Au droplets show the opposite trend of increased size with correspondingly decreased density as a function of the annealing temperature due to the difference in the diffusion length of adatoms at varied activation energy. Under an identical growth condition, depending on the surface index, the size and density of Au droplets show a clear distinction, observed throughout the temperature range. The results are systematically analyzed and discussed in terms of atomic force microscopy (AFM) images, cross-sectional line profiles, and Fourier filter transform (FFT) power spectra as well as the summary plots of the size and density.     

Performance Characteristics of a Drying Heat Pump Using Superheated Steam

ABSTRACT

A complete mathematicalhumerical model is proposed, in order to simulate the performance characteristics of a novel concept of a drying heat pump based on the theory of minimum energy cyclcs. The drying heat pump involvcs vapour condensation in a Lava1 nozzle. removal of the liquid phase in a supersonic separator as well as compression of the working medium. which is superheared vapour.     

Annealing temperature effect on self-assembled Au droplets on Si (111)

We investigate the effect of annealing temperature on self-assembled Au droplets on Si (111). The annealing temperature is systematically varied while fixing other growth parameters such as deposition amount and annealing duration clearly to observe the annealing temperature effect. Self-assembled Au droplets are fabricated by annealing from 50°C to 850°C with 2-nm Au deposition for 30 s. With increased annealing temperatures, Au droplets show gradually increased height and diameter while the density of droplets progressively decreases. Self-assembled Au droplets with fine uniformity can be fabricated between 550°C and 800°C. While Au droplets become much larger with increased deposition amount, the extended annealing duration only mildly affects droplet size and density. The results are systematically analyzed with cross-sectional line profiles, Fourier filter transform power spectra, height histogram, surface area ratio, and size and density plots. This study can provide an aid point for the fabrication of nanowires on Si (111).