Another factor that should be taken into consideration is the droplet size, which is mainly affected by the flow rate and gas pressure. Kim et al. [36] investigated the influence of spray condition on the droplet size and found that the sprayed droplet size would decrease with increasing gas pressure. The relationship between droplet size and spray height is depicted by the formula (2) where D av is the average droplet diameter, W is the average drying rate of the droplet, λ is the latent heat of vaporization, k d is the thermal conductivity of the liquid droplet, and ∆T is the mean temperature difference between the droplet surface find more and the surrounding air [37]. To avoid the diffraction of the sprayed

droplet on the pattern, spray height should be set lower than 10 cm. However, a droplet of large size (>30 μm) would be formed in this situation, which may in turn result in large time consumption for film drying. Meanwhile, the overlapping between several droplets could lead to a rough surface and insufficient sintering of silver nanoparticle inks. In this case, decreasing the flow rate

below 1.1 ml/min was necessary to obtain the droplet size with a diameter of approximately 15 μm [38]. After optimizing the spray operating condition, the conductive patterns were finally accurately spray-coated, as shown in Figure 2a. Figure 2 Metallurgical BIBW2992 clinical trial microscope images of the rim of the inkjet-printed (a, b) and spray-coated (c, d) conductive silver patterns. Compared to inkjet printing, spray coating has an obvious advantage on fabricating accurate patterns. Figure 2a shows the wave-like edge of inkjet-printed patterns, which is mainly attributed to the drop-to-drop distance and component of the solvent. As depicted in Figure 2b, the 10-μm inkjet-printed line is along the 1.5 ~ 3-μm scalloped edge. If the adjacent conductive lines were set closer than 3 μm, the wave-like edge would result in the crosstalk of electrical signal or even worse [25]. Figure 2c reveals a spray-coated silver line with a width of 20 μm, while the edge

of the silver line is only 1 Mirabegron μm. It also shows that the edge of the spray-coated line is composed of a mass of silver dots, resulting from the inevitable diffraction of the spraying process. The enlarged view exhibits that the majority of divergent dots are isolated with each other. This indicates that the edge of spray-coated patterns is not conductive, which guarantees the potential of spray-coated silver nanoparticle inks for fabricating accurate patterns in the scale of nanometer. Figure 3 shows the electrical properties of conductive patterns and the relationship between sintering temperature and the time consumption of the sintering process. The transparent ink would turn into black in initial several seconds and then reflect the bulk silver metallic luster after the integrated sintering process.