Capillary Pick-and-Place of Glass Microfibers

Microfibers are key components in construction of fiber-based materials, biomimetic materials, microsensors, and other fiber-based microstructures. Due to the scaling law, the adhesion forces such as van der Waals force or electrostatic force in the micro world play a more dominant role than the gravity, causing difficulties in precise pick-and-place of the micro objects. In this paper, we propose a capillary force-based pick-and-place method for handling microfibers. The method combines the typical robotic transportation technique and capillary gripping method to achieve fast and accurate pick-and-place of microfibers. We quantitatively analyzed the critical conditions for capillary pick-up and placement of microfibers and validated the technique experimentally. The theoretical analysis indicates that both pick-up and the placement of microfibers are largely dependent on the contact length on the fiber or the contact angle of the meniscus on the substrate. The experimental results show that the microfibers can be reliably picked up from and placed on the substrate of different materials including paper tissue, glass, silicon, stainless steel, copper with droplet volume of 0.1 nL and 0.3 nL. We further applied the method to the placement of the microfibers on super hydrophilic-super hydrophobic grooves and studied its placement speed and accuracy. We demonstrated that microfiber can be placed in such grooves in less than 0.1 seconds, with linear placement accuracy of $10~\mu \text{m}$ and angular placement accuracy of 0.5°. The proposed method is fast and simple, and it is especially suitable for handling fragile and flexible micro sized objects and construction of fiber-based materials.