Research On Self-bending Alignment Micromanipulation Of Flexible Microfibers Based On Capillary Force

Flexible microfibers are a class of micron-scale fiber materials with special flexibility,high plasticity,and excellent mechanical properties.These properties endow flexible microfibers with great potential and enormous economic and societal value for applications in biomedical,intelligent materials,and environmental management fields.However,precisely controlling these high aspect ratio flexible microfibers and arranging them into complex patterns remains a challenging task.Previous micro manipulation research has mainly focused on rigid objects at the microscale,such as microchips and microparticles,with relatively little research on the transportation and placement of flexible objects.Therefore,this paper proposes a micro manipulation method for flexible microfibers that can utilize liquid capillary forces to drive microfibers to undergo bending at the microscale and then align them with hydrophilic microgrooves to achieve patterned layouts.The main research contents are as follows.(1)Simulation of the profile curve of the liquid bridge using a double iterative algorithm leads to the simulation values of the pick-up force of the liquid bridge.The simulation results show that the pickup force increases with the increase of the contact line length,while it decreases with the increase of the liquid bridge height.When the pickup force is less than 9.1×10-4 μN,the liquid bridge cannot achieve the pickup of microfibers.The mechanical analysis and simulation of the self-bending alignment process of flexible microfibers is carried out,and the selfbending alignment process of flexible microfibers consists of two parts:selfrotation and self-bending.And the effects of liquid volume on self-rotation and contact line length on self-bending during the motion are discussed.The simulation results show that the results show that the microfiber can self-rotate when the width of the microgroove is 40 μm and the volume of liquid in the microgroove reaches 573 μL,and the microfiber can self-bend when the length of the microfiber is 12.5 mm and the contact line length is 9.81 mm.The simulation study of self-bending found that the liquid bridge can provide enough recovery force and recovery torque to align the flexible microfibers for self-bending only when there is sufficient liquid in the microgroove.In addition,it is found that the reaction torque caused by friction between the microfibers and the substrate is much larger than the recovery torque of the liquid bridge,i.e.,the self-bending alignment cannot occur when the microfibers and the substrate are in contact.(2)Hydrophilic microsinks with adjustable wettability were prepared by UV laser.In addition,the relationship between microsink wettability and processing line spacing and laser speed was also investigated.The results show that the wettability of the microsink increases with the increase of the processing line spacing and laser speed,and the amount of liquid that the microsink can confine decreases with the increase of the microsink wettability as the contact angle of the microsink increases from 5° to 18.7° with the increase of the processing speed from 1000 mm/s to 4500 mm/s.(3)A series of microfiber pickup,release and self-bending alignment experiments were completed.Firstly,microfiber pickup experiments were conducted using the liquid without mentioning the volume,and the results showed that the pickup could be completed on any wettable surface when the liquid was less than 0.3 μL,and only on superhydrophobic surfaces when the liquid was larger than 0.3 μL.Secondly,self-bending alignment experiments of microfibers in hydrophilic microgrooves with different wettability were carried out,and the results showed that the self-bending success rate of microfibers was 100%when the contact angle of microgrooves was less than 5°.With the increase of fiber length and microgroove radius,the success rate of self-bending alignment of microfibers was increased and then decreased.Finally,the effect of the position error on the alignment accuracy during the self-bending alignment process was analyzed.With the decrease of fiber length and microgroove radius,the error of self-bending alignment decreased,and the minimum deviation was 0.74 μm in the X direction and 1.2 μm in the Y direction,which realized the accurate alignment of flexible microfibers.