Heterogeneous substrates with moderate and extreme wettability contrasts were fabricated by comprising of superhydrophobic/hydrophilic and superhydrophobic/extremely hydrophilic surfaces, respectively. The interactions of water droplets impinging on the surfaces with sharp wettability contrasts were investigated experimentally. The impinging droplets that slightly touch the hydrophilic or extremely hydrophilic areas on each substrate exhibit a directional rebounding towards the more wetting surfaces, i.e., hydrophilic or extremely hydrophilic surface. The trajectory and landing distance of the rebounded droplets were tailored by controlling the releasing height of the droplet, wetting contrast across the border, and portion of the droplet touching the more wetting surface of the substrates with wettability contrasts. The landing distance of the droplet increases with the increased releasing height and higher wettability contrast across the border. Increasing the portion of the impinging droplet touching the more wetting surface of the heterogeneous substrates leads to the shorter landing distance of rebounded droplets.
Nanowires are widely used as sensing components for lab-on-a-chip devices. One major problem in utilizing pre-grown nanowires in lab-on-a-chip applications is the agglomeration of nanowires during their preparation process. The common methods to reduce the agglomeration of nanowires include stirring, sonication and using of surfactants. However, these methods break the long nanowires and are not efficient to produce enough single nanowires. This paper shows a new method to improve the deposition process of individual nanowires. An intermediate membrane was used for the deposition of the nanowires after their preparation process. The membrane helps to filter the nanowire agglomerates and to deposit separated individual nanowires over a silicon surface underneath. The study also shows that the number of single nanowires is increased by increasing the tilt angle of the membrane. The method also helps achieving single long nanowires.
Alignment and placement of a single nanowire is a crucial task to assemble lab-on-a-chip devices. Nanowires placement techniques have been mostly performed by pick and place techniques or flow control techniques. These techniques require expensive control systems and they cannot be performed in the ambient conditions. This paper introduces a vision-based inexpensive approach for the alignment and placement of individual metal nanowires on a target nanochannel. Through visual observation of the optical microscope, the method aligned the nanowire perpendicular to the nanochannel. The reproducibility of the procedures was experimentally evaluated.
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