A Novel Biomimetic Nanocomposite Exhibiting Petal Wetting Phenomenon: Fabrication and Experimental Investigations

A functional composite material that simultaneously exhibits hydrophobicity and water droplet adhesion has monumental potential in controlling fluid flow, studying phase separation, and biological research. This article reports the fabrication of a petal wetting biomimetic Boron Nitride Nanotubes (BNNTs) -Polydimethylsiloxane (PDMS) nanocomposite achieved by drop casting. The petal effect was investigated by non-destructive techniques. The nanotubes were synthesized by chemical vapor deposition at 1150 °C and were characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The mean diameter of the nanotubes was found to be 70 nm. The nanocomposites had BNNT fillers ranging from 0.5 wt. % to 2 wt. %. Water contact angles for pure PDMS polymer was 94.7° and for the 2 wt. % BNNT-PDMS nanocomposite was 132.4°. The petal wetting nanocomposite displayed a characteristic trait of high contact angle hysteresis. The surface roughness parameters of the nanocomposites were determined by atomic force microscopy. Laser scanning confocal microscopy aided in analyzing the droplet penetration and in observing the trapped air between the water droplet and the nanocomposite surface. Based on surface observations, roughness parameters, and the extent of droplet penetration by the surface, we shed light on the Cassie impregnating wetting regime followed by the biomimetic nanocomposite. Such a surface would be beneficial in the study of the embryogenesis of cells and aid in moisture collection.

Large-eddy simulation of droplet-laden cough jets with a realistic manikin model

Three-dimensional computational fluid dynamic (CFD) methods were used to simulate a cough jet that contains droplets. The turbulent cough flow is modelled using large-eddy simulation with a dynamic structure model. An Eulerian–Lagrangian approach was adopted to model the two-phase flows. Droplet breakup, evaporation, dispersion and drag forces were considered in the model. Two different inlet velocity profiles, which are based on constant mouth opening area and variable mouth opening area, were considered in the CFD model. The numerical model was validated by comparing with the available experimental measurements. The results show that the use of the fixed mouth opening area in the geometric model shows the inlet velocity profile of the ‘variable area’ matched better with the experimental data than with the ‘constant area’ inlet velocity profile. Droplet dynamics were analysed with a focus on the droplet penetration and droplet distribution in space during the whole coughing process. The droplet penetration shows two-stage profiles, both of which can be described by logarithmic functions. This is consistent with the analytical results of the simplified drag model. The droplets generated during the mouth opening or closing periods have a higher velocity and longer droplet penetration. With a higher room temperature, the droplet penetration is shorter.

Application of transparent microperforated panel to acrylic partitions for desktop use: A case study by prototyping

There are various measures currently in place to prevent the spread of COVID-19; however, in some cases, these can have an adverse effect on the acoustic environment in buildings. For example, transparent acrylic partitions are often used in eating establishments, meeting rooms, offices, etc., to prevent droplet infection. However, acrylic partitions are acoustically reflective; therefore, reflected sounds may cause acoustic problems such as difficulties in conversation or the leakage of conversation. In this study, we performed a prototyping of transparent acrylic partitions to which a microperforated panel (MPP) was applied for sound absorption while maintaining transparency. The proposed partition is a triple-leaf acrylic partition with a single acrylic sheet without holes between two MPP sheets, as including a hole-free panel is important to a possible droplet penetration. The sound absorption characteristics were investigated by measuring the sound absorption in a reverberation room. As the original prototype showed sound absorption characteristics with a gentle peak and low values due to the openings on the periphery, it was modified by closing the openings of the top and sides. The sound absorption performance was improved to some extent when the top and sides were closed, although there remains the possibility of further improvement. This time, only the sound absorption characteristics were examined in the prototype experiments. The effects during actual use will be the subject of future study.

Application of transparent microperforated panel to acrylic partitions for desktop use: A case study by prototyping

There are various measures currently in place to prevent the spread of COVID-19; however, in some cases, these can have an adverse effect on the acoustic environment in buildings. For example, transparent acrylic partitions are often used in eating establishments, meeting rooms, offices, etc., to prevent droplet infection. However, acrylic partitions are acoustically reflective; therefore, reflected sounds may cause acoustic problems such as difficulties in conversation or the leakage of conversation. In this study, we performed a prototyping of transparent acrylic partitions to which a microperforated panel (MPP) was applied for sound absorption while maintaining transparency. The proposed partition is a triple-leaf acrylic partition with a single acrylic sheet without holes between two MPP sheets, as including a hole-free panel is important to a possible droplet penetration. The sound absorption characteristics were investigated by measuring the sound absorption in a reverberation room. As the original prototype showed sound absorption characteristics with a gentle peak and low values due to the openings on the periphery, it was modified by closing the openings of the top and sides. The sound absorption performance was improved to some extent when the top and sides were closed, although there remains the possibility of further improvement. This time, only the sound absorption characteristics were examined in the prototype experiments. The effects during actual use will be the subject of future study.

A Bias Gantry Profiling Boom Sprayer for Orchard Protection

An air-assisted sprayer sends liquid medicine to a canopy of orchard plants for protection. However, the inherent drift in this method lowers the pesticide utilization. To meet the gardening requirements of a short-anvil densely planted apple orchard, a profiling boom sprayer was designed, and the operation requirements and prototype operation parameters of plant protection were determined. The droplet depositions in the upper, middle, and lower layers of the targets and in the inner, middle and outer rings were analyzed in field experiments. The standard deviations of the droplet deposition coverage rates on free, slender, and high spindles at different heights were 4.43, 2.82, and 5.29, respectively, and those of the droplet deposition densities were 5.97, 4.98, and 6.15, respectively. All p-values exceeded 0.05, indicating that droplets from the outer ring were uniformly distributed at different canopy heights. The average droplet deposition density exceeded 150 grains·cm-2 in the outer and center rings of the three tree-shaped targets, and reached 100.60 grains·cm-2 in the inner ring. The droplet deposition coverage rates on the free, slender, and high spindles in the inner ring were 37.41%, 36.69%, and 35.47%, respectively, indicating that the droplet penetration ability of the profiling boom sprayer meets the requirements of plant protection. The developed profiling boom sprayer has improved the inherent serious drift problem of the air blower sprayer, and has provided inspiration for the research and development of orchard plant protection machinery.Materials and Methods: water-sensitive paper produced by Liuliu Shanxia Plant Protection Technology Co., Ltd. (China); the profiling boom sprayer; a tractor; a wind-speed measuring instrument (AS856S, Shanghai Xima Technology (Group) Co., Ltd., Shanghai, China); a temperature and humidity measuring instrument (RC-4, Jiangsu Jingchuang Electric Co., Ltd., Jiangsu, China);, double-sided tape; a box ruler; a stopwatch and a scanner. The water-sensitive paper was cut into 3 cm × 2 cm rectangular units, and its back side was pasted to the apple trees of the test target with a small amount of double-sided tape. Facing the east, south, west, and north directions, papers sprayed by the inner, middle and outer rings were pasted on the top, middle and bottom layers of the fruit tree canopy (Dong et al., 2018, Fig.5a). To avoid disturbance from spray drift, six fruit trees were selected as the test targets at intervals of their tree shapes, and 648 water-sensitive papers in total were pasted.Results: After averaging over height, the standard deviations of the droplet deposition coverage rates of the free, slender, and high spindles were 4.43, 2.82, and 5.29 respectively, and those of the droplet deposition density were 5.97, 4.98, and 6.15 respectively. All p-values exceeded 0.05. The average droplet deposition densities of the three tree-shaped targets exceeded 150 grains·cm-2 in the center and outer rings. The average droplet deposition density in the inner ring was 100.60 grains·cm-2, and the droplet deposition coverage rates of the free, slender, and high spindles were 37.41%, 36.69%, and 35.47%, respectively. Averaged over the four directions, the coverage rate in the outer ring was 41.46% higher than in the center ring, and 90.87% higher than in the inner ring. Meanwhile, the average coverage rate was 34.93% higher in the center ring than in the inner ring.Discussion: The outer ring of the profiling boom sprayer evenly distributed the droplets at different heights. The growths of the droplet deposition coverage rates were similar, and the droplet penetrations in different rings were consistent. Although the droplet penetration of the inner ring was poorer in the horizontal than center and outer ring in the vertical direction, the blades of the inner ring were sprayed sufficiently to meet both the quality assessment of plant protection operations and the design operating requirements of the profiling boom sprayer.

Application of transparent microperforated panels to acrylic partitions for desktop use: A case study by prototyping

There are various measures currently in place to prevent the spread of coronavirus (COVID-19); however, in some cases, these can have an adverse effect on the acoustic environment in buildings. For example, transparent acrylic partitions are often used in eating establishments, meeting rooms, offices, etc., to prevent droplet infection. However, acrylic partitions are acoustically reflective; therefore, reflected sounds may cause acoustic problems such as difficulties in conversation or the leakage of conversation. In this study, we performed a prototyping of transparent acrylic partitions to which a microperforated panel (MPP) was applied for sound absorption while maintaining transparency. The proposed partition is a triple-leaf acrylic partition with a single acrylic sheet without holes between two MPP sheets, as including a hole-free panel is important to prevent possible droplet penetration. The sound absorption characteristics were investigated by measuring the sound absorption in a reverberation room. As the original prototype showed sound absorption characteristics with a gentle peak and low values due to the openings on the periphery, it was modified by closing the openings on the top and sides. The sound absorption performance was improved to some extent when the top and sides were closed, although there remains the possibility of further improvement. For this study, only the sound absorption characteristics were examined in the prototype experiments. The effects during actual use will be the subject of future study.