Direct Writing Micro-concave Structure With Viscoelastic Substrate And Its Application

Micro-structured films,as a novel class of functional materials,gained increasing importance in various fields including electronics and biomedicine.A key aspect for the preparation of patterned micro-structured surfaces was the regular deposition and diffusion of droplets on the substrate.In this regard,direct writing technology emerged as a simple,convenient,cost-effective,and environmentally friendly method for micro-structure fabrication by using ink materials with shear-thinning properties.This technique allowed for ink transfer onto the substrate and the formation of the desired micro-structure through infiltration deposition,by adjusting the ink viscosity and printing conditions.Based on material extrusion,direct writing technology offered simplicity in manufacturing,material adaptability,and cost-effectiveness,making it a promising approach for the preparation of three-dimensionally patterned microchannels,microfluidics,and biological organs.This thesis aimed to investigate the printing conditions of direct-printed micro-concave structured surfaces and explore their potential applications.The research included the following studies:（1）In the first part,the direct writing technique was employed to prepare patterned micro-concave structure arrays on PDMS viscoelastic substrates.The investigation focused on identifying the key factors affecting the preparation process.To achieve a controlled preparation of the depressed micro-structure morphology,experimental conditions such as pre-curing time of the viscoelastic substrate,PVA ink concentration,printing pitch,number of printing layers,and nozzle diameter were optimally selected to control the behavior of the ink droplets during spreading and deposition.Notably,an optimized precuring temperature of 70°C,precuring time of 8min,and a PVA to H₂O mass ratio of 1:8 led to the production of micro-concave structure morphology that was well-defined and uniformly arranged.The scanning of the micro-concave structure morphology using a step meter revealed a depth of up to 45μm and a width of up to 50μm.This indicates that the direct writing technique could effectively produce micro structured surfaces with specific depression morphology under the optimized conditions.Overall,this study provides a novel and valuable method for preparing micro-structured surfaces with particular depression morphology.（2）In the second part,micro-concave structured films fabricated via direct writing were utilized for exploratory investigations on liquid adsorption and release,preparation of complex shaped micro-convex structured templates,and deposition of silver nanowires to create flexible electrodes.In the experiments,methylene blue solution droplets were placed on the surface of plasma-treated PDMS films,and the capillary effect of the micro-pit structure was utilized to adsorb the solution into the recessed micro-structure.The PDMS film filled with the methylene blue solution was subsequently applied to the skin,and the release of the methylene blue solution was observed.Additionally,silver nanowires were deposited on the film with the array of micro-concave structures to produce a flexible electrode.The tensile displacement of this flexible electrode was 10.2 mm,the tensile strain rate was 41%,and the maximum strain value was 8.193 N as determined via tensile testing.Finally,using the micro-concave structure film as a template,a film with an array of micro-convex structures was obtained via PDMS complex casting.（3）In the third section,the present study investigates the direct writing parameters and printability of patterned microgrooves on PDMS viscoelastic substrates using direct writing technique,and discusses the anisotropy of the micro-groove structure surface.The study optimized various experimental conditions such as sacrificial ink type,pre-curing time of the viscoelastic substrate,and printing parameters（e.g.,printing speed,nozzle diameter,etc.）to control the behavior of the ink during spreading and deposition,and achieve a controllable preparation of patterned recessed micro-structures.The micro-groove structures were distinctly shaped and uniformly arranged when direct-written printing on PDMS substrates was carried out at a PDMS precuring temperature of 70°C,a precuring time of 8min,and a mass ratio of 1:2 between PAA and anhydrous ethanol.Furthermore,the surface of the micro-groove structure was dipped in silicone oil to achieve a sliding surface,and the sliding angle was tested to reveal the anisotropy of the microgroove structure surface.To summarize,this study successfully prepared patterned surfaces with recessed micro-structures using controlled deposition and diffusion of liquid droplets on the substrate.The precuring time of the viscoelastic substrate,concentration of sacrificial ink,and various printing parameters were controlled to modulate the deposition behavior of the droplets and obtain a controlled and homogeneous array of micro-concave structures.These structures were investigated for their potential applications in droplet adsorption and release,template reshaping,and flexible electrodes.Additionally,the study varied the set-up procedure and printing parameters to prepare surfaces with microgroove structures,which were then immersed in silicone oil to create anisotropic slip surfaces.This topic has significant implications for the preparation of patterned recessed micro-structured surfaces.