Preparation Of Graphene-based Flexible Electronics By Stress-assisted Laser Direct Writing PDMS/PI

Flexible Electronics Technology has broad development prospects in the fields of health detection,medical equipment,sensors and so on.The corresponding flexible devices have high flexibility requirements for their hardware,and various flexible structures and flexible electronic conductors have been developed one after another.When laser-induced graphene（LIG）is used as a flexible electronic conductor,its potential in stretching applications is limited due to the lack of stretching properties of its substrate polyimide（PI）.In this thesis,polydimethylsiloxane（PDMS）and PI are used as composite flexible material substrates,and a new method of stress-assisted laser-induced graphene is proposed to fabricate stretchable LIGs.The following is the specific research content.First,the stress-assisted stretching mechanism is designed.Flexible materials such as PDMS have large deformation and uneven force during the stretching process.A device that can stretch in multiple directions is designed.The bidirectional screw rods are arranged vertically and crossed to obtain four mutually perpendicular motion directions;combined with the structural characteristics of the well-shaped guide rail,the two mutually perpendicular motions are combined into a combined motion along the direction of the angle bisector to realize the synchronization of eight directions sports.Combined with the drive control module and necessary auxiliary connectors,the overall construction of the stretching mechanism is completed.The controller controls the movement speed and direction of the clamping part,and uses the reducer to achieve smooth and slow movement with a movement speed of0.6mm/min.Second,a laser-induced graphene PDMS/PI composite flexible substrate system was constructed.PDMS has flexibility but low carbon source,PI has abundant carbon source but not stretchable,combining the advantages of both to build a composite substrate system.In this paper,two kinds of PI powders were used for experiments.Observation of the surface to be processed and spectral analysis of the hybrid material system confirmed that the surface material of the system was PDMS;the cross-sectional observation of the PI powder showed that there was sedimentation in the composite material system,and the maximum area of the powder accounted for 75.35%.The material tensile test was carried out to obtain the tensile strength（0.54MPa-0.98 MPa,0.96MPa-2.88MPa）and the maximum deformation（29.73%-90.22%,118.56%-157.98%）,stress-strain curve and Young’s modulus（2.16MPa-7.05 MPa,2.31MPa-5.30MPa）,the test results show that the tensile fracture position of the material mainly occurs at the position of powder agglomeration and sample clamping.Thirdly,the study and analysis of the stress-assisted laser-induced graphene forming law.Laser-induced graphene（LIG）was detected by Raman spectroscopy and the lattice structure of graphene was observed.There were significant D,G,and 2D peaks in the spectrum,and the lattice fringe gap was 0.31nm-0.36 nm.A single laser direct writing experiment was carried out.The experimental results showed that the processing line width increases with the increase of laser power（10%-50%）.The minimum line width is 342.79μm and 333.54μm,and the maximum line width is 534.44μm and 521.39μm.;The processing line width decreases with the increase of scanning speed（80mm/s-240mm/s）,the maximum line width is 544.19μm and560.36μm,and the minimum line width is 401.50μm and 411.03μm.Single-factor experiments were carried out to observe and record the layer thickness information and geometric dimensions of LIG under different parameters,and to analyze and compare the influence of auxiliary stress conditions on the layer thickness and geometric dimensions of LIG.The results of the single-factor laser power experiment found that the extrusion effect of internal stress increases the layer thickness of LIG in the forming direction parallel to the stress-assisted direction,the increase range is 10μm～26μm,and the corresponding geometric size decreases,and the reduction range is 0.45mm～0.85 mm.In the forming direction perpendicular to the stress-assisted direction,the layer thickness decreases by 12μm～22μm,and the corresponding geometric size increases,and the increase range is 0.08mm～0.14 mm.Finally,the LIG layer is tested for electrical properties and fatigue detection.Apply a silver coating on both ends of the LIG layer as the measurement area,measure and record the resistance value of the LIG layer,and compare and analyze the resistance change of the LIG layer under stress-assisted conditions.Parallel stress-assisted conditions can reduce the resistance of LIG by 0.16KΩ～0.26KΩ.Large strain（13.33%）and vertical stress-assisted conditions destroy the LIG layer structure and increase the resistance by 0.1KΩ～0.5KΩ.The LIG layer was encapsulated by PDMS,and then bending and tensile tests were performed to record the resistance change information during the LIG deformation process.Comparative analysis found that the stress-assisted conditions of small strain and parallel tension were beneficial to improve the tensile properties of the LIG layer.Compared with the tensile test of the LIG layer without tension,the resistance increase ratio is reduced by about 15%.