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Acoustic levitation status and thermal infrared photography of the ZIF-8 synthesis process: (a-c) initial, intermediate and final states of levitating synthesis; (d-i) thermal infrared images at various moments.
Source publication
Zeolitic imidazolate framework-8 was synthesized in a containerless state via acoustic levitation. The cavitation effect of ultrasound affected the coordination connection of organic ligands in acoustically levitated droplets and they exhibited a conspicuous difference in the particle size distribution as compared with those under normal conditions...
Contexts in source publication
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... independently developed single-axis acoustic levitator is used to synthesize the ZIF-8, and the ultrasonic waves form a standing wave field between the emitter and reflector to balance the weight of the sample to achieve levitation. (Fig. 1) The ultrasonic frequency was 21.3 kHz and the ultrasonic power was 350 W. In the case of acoustic levitation, 64.89 mg of 2-methylimidazole and 29.33 mg of Zn(NO 3 ) 2 Á6H 2 O were dissolved in 2 mL of methanol, respectively (initial concentration is provided in Table 1). A pipette was used to transfer 30 mL of 2-methylimidazole ...
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... waves on the material was usually to produce smaller particles. 9,11 The influence of concentration changes on the particle size caused by evaporation during acoustic levitation should also be considered. It is worth noting that the solvent in our synthesis was volatile methanol, and the evaporation of acoustically levitated droplets was obvious (Fig. 1a-c). Under normal conditions, the particle size gradually increased with the increase in concentration. 20 Therefore, the evaporation of methanol in this situation was an important factor which influenced the ZIF-8 ...
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... Chem. Chem. Phys., 2023, 25, 17798-17807 | 17801 transformation and temperature evolution (Fig. 1d-i) of acoustically levitated droplets. The volume of the droplet was calculated according to the geometrical dimensions, and the volume changes can reflect the concentration changes. The equatorial radius, the thickness and the location height of the levitated droplet were obtained through image analysis. Within 15 minutes, the ...
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... 16 In this experiment, the volume of the levitated droplet was 60 mL. A greater acoustic radiation force acting on the droplet surface was needed to achieve levitation, and the shape of the acoustically levitated droplet was oblate. As the droplet evaporated with time, the intense acoustic radiation force caused the droplet to become a flat disk (Fig. 1d-i). In this case, the natural convection caused by gravity and the Marangoni flow induced by surface tension was suppressed. In the presence of a high-frequency acoustic field, the acoustic radiation force was dominant rather than surface tension, and the droplet didn't become spherical. The steady streaming at the surface of the droplet ...
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... In the presence of a high-frequency acoustic field, the acoustic radiation force was dominant rather than surface tension, and the droplet didn't become spherical. The steady streaming at the surface of the droplet originated in a thin shear-wave layer, known as the Stokes layer, and the external streaming developed into the main fluid. 22 In Fig. 1d-i, the stratification and temperature increase of the droplet surface via thermal infrared photography also indicated the strengthening of external streaming to some extent; besides there was also a part of the environmental heat transfer to the droplet. The calculated volume is shown in Fig. 4b; the volume was just quarter of the ...
Citations
We, herein, present dynamic behaviors of droplets entering an ultrasonic standing wave field (19 800 Hz) at different angles. In experiments, droplets’ motion is recorded by using a high-speed camera, and an in-house Python program is used to obtain droplet positions and morphological characteristics as functions of time. The experimental results indicate that when the sound intensity is lower than the instability intensity and higher than the levitation intensity, the vertically falling droplet will oscillate up and down based on the equilibrium position. Although the oscillation amplitude decays from 0.52Tl to 0.01Tl (Tl = λ/2, λ is the wavelength) under the action of viscous resistance, the oscillation frequency of the droplet remains unchanged. Meanwhile, as the droplet’s position oscillates, the acoustic radiation force on the droplet also periodically fluctuates, resulting in the acoustically forced oscillation of the droplet shape. In addition, when the droplet enters the sound field with a horizontal tilt angle θ of 15°, it undergoes a V-shaped translational motion, first descending and then ascending. As the sound pressure amplitude increases, the rebound position of the droplet advances. When the sound pressure amplitude reaches the instability value (7900 Pa), the droplet undergoes right-hand and left-hand disintegration during its descent and ascent, respectively. This instability is due to the acoustic radiation pressure distribution and the droplet’s V-shaped trajectory. This work comprehensively discussed the complex motion of moving droplets in the acoustic standing wave field, which may inspire revealing the spray motion in the liquid engine with high-intensity resonance.
