Research On Laser Microfabrication Technology Of Hydrophilic And Hydrophobic Patterns For Micro-Operation

The method of micro-manipulation using liquid surface tension is becoming more and more popular because it has the advantages of high operational efficiency,reduction of impact and local stress on the substrate,and self-alignment of the chip.The prerequisite for this micromanipulation is the tunable wettability of the substrate.Most of the existing methods to change the wettability of the material surface have problems such as environmental pollution,high processing cost,and complicated operation process.To address the above problems,this thesis proposed an efficient and green preparation method for changing the surface wettability of silicon and stainless steel substrates using a microsecond pulsed laser marking machine.The laser acts on the substrate surface and makes the wettability of the substrate adjustable by changing the microstructure of the substrate surface.And on this basis,liquid directional transfer,microchip selfalignment and fog water collection experiments were conducted.The main research contents are as follows:(1)The laser processing process is analyzed.A pulsed laser is used to process on the substrate surface,and the area irradiated by the laser spot is the scanning area,in which the substrate material can be removed;the area not irradiated by the laser spot is the non-scanning area,and the laser does not affect the non-scanning area.The effects of laser processing speed,processing times,current magnitude and out-of-focus amount on the microscopic morphology of silicon substrates were investigated under laser processing of a single line segment.Combining the laser processing parameters,Cassie’s theoretical model and the nature of the superhydrophobic coating material,a processing process to modulate the surface wettability of the silicon substrate was developed.The wettability of the silicon substrate in the processing area is controlled by controlling the area share of the superhydrophobic coating in the processing area removed by laser scanning.The effects of laser processing speed,scan line spacing and defocusing amount on the wettability of the processed area were investigated.The experimental results show that as the processing speed increases from 100 mm/s to 9000 mm/s and the scanning line spacing increases from 20 μm to 150 μm,the removal area share of the processed area decreases and the contact angle gradually increases from below 5° to 127°;as the absolute value of the distance between the substrate surface and the laser focal plane increases from 0 mm to 3 mm,the contact angle of the processed area increases from below 5° to above 170°.to more than 170°.(2)The effects of laser processing speed,processing times and current magnitude on the microscopic morphology of stainless steel substrates under a single line segment of laser processing were investigated.Combining the results of processing under a single line segment with the Wenzel theoretical model,a processing process for wettability modification of stainless steel substrates was developed.A laser is used to build microstructures on the substrate surface,and then a low surface energy substance is used to modify the surface chemical modification,which in turn changes the wettability of the substrate surface.The wettability of the stainless steel surface was successfully modified by this process to over 156°.The transformation of the wetting state of liquids with different surface tensions on the stainless steel substrate surface was investigated.The results showed that the substrate surface with a grid-shaped groove microstructure was processed at a scan line spacing of 50 μm and the substrate surface with a crater-shaped array microstructure was processed at a processing speed of 2000 mm/s.The droplet surface tension of the droplet was greater than 50 mN/m,and the droplet on the substrate surface was more stable in the Cassie state.The droplets on the substrate surface were more stable in the Cassie state when the surface tension of the droplets was greater than 60 mN/m for the substrate surface with a grid-shaped groove microstructure processed at a scan line spacing of 20μm and the substrate surface with a crater-shaped array microstructure processed at a processing speed of 7000 mm/s.The droplets on the substrate surface were more stable in the Cassie state when the surface tension of the droplets was greater than 60 mN/m.(3)Based on the above experimental results,silicon substrates and stainless steel substrates with no wettability partitioning were prepared,and a series of substrate testing experiments were carried out.The experiments include droplet directional transport experiments and microchip self-alignment experiments on silicon substrates,and droplet directional transport experiments and fog-water collection experiments on stainless steel substrates.The results of the droplet directional transport experiments on silicon substrates show that droplets can be transported along the curved trajectory by processing on silicon substrates,and the droplet directional transport is successfully achieved;the results of the microchip self-alignment experiments on silicon substrates show that the silicon substrates with adjustable wettability can confine a quantitative amount of droplets and meet the conditions of chip self-alignment,and the microchip self-alignment experiments are successfully conducted and the chip is used to pose The experimental results of droplet directional transport on stainless steel substrate show that the processed stainless steel substrate with wedge pattern and different wettability partitions can realize the directional transport of droplets,and there is a Laplace pressure gradient of droplets on the superhydrophilic wedge pattern to drive droplet transport from the tip to the bottom;the experimental results of fog water collection on stainless steel substrate show that the stainless steel substrate with different wettability partitions has higher fog-water collection efficiency.