Study On Surface Microstructure Of Pmma Written Directly By Femtosecond Laser And Its Influence On Hydrophobicity

Polymethyl methacrylate（PMMA）has been widely used in various fields of human production and life,especially used in biomedicine as biomedical composite materials for artificial bones,joints and artificial lenses.However,due to its poor surface hydrophobicity,bacterial infection and local inflammation can be easily caused when PMMA adsorbs proteins in the environment of biological tissues,which limits its application in biomedicine.Therefore,it is of importance to improve the hydrophobicity of PMMA.Based on Cassie’s wetting model,the hydrophobic properties can be further improved by creating microstructure on the surface of the material.Considering the advantages of high precision and low thermal effect,femtosecond laser direct writing technique has been used to construct various microstructures on PMMA material surface.Based on this,good hydrophobic properties of PMMA can be achieved by designing scientific microstructures on PMMA surface and fabricating microstructures using femtosecond laser direct writing technology.This research has important guiding significance and high application value.The main research work and achievements are as follows:1.Considering the latent heat of vaporization,thermal decomposition and moving laser Gaussian heat source of PMMA,the transient temperature field model of PMMA processed by femtosecond laser was established by using finite element Comsol,and the effects of laser power and scanning speed on the temperature field of PMMA workpiece surface were analyzed.Based on the laser heating temperature distribution of PMMA,the formation of ablative grooves during laser machining was analyzed,and the relationship between laser power,scanning speed and groove size was revealed,which provides technological guidance for laser-based preparation of single channel groove on PMMA surface.2.A self-designed femtosecond laser machining system controlled by 3D platform was constructed.On the basis of finite element analysis,femtosecond laser was used for PMMA direct writing experiment,and the influence of laser power,scanning speed,pulse frequency and scanning times on groove size was analyzed.The ablation morphology of PMMA was analyzed by SEM and EDS.The results showed that the laser power and scanning speed had great influence on the width and depth of the groove.Through establishing the width model and depth model of PMMA groove processed by femtosecond laser,it could be known that the groove size was basically consistent with the finite element results.Using laser direct writing technology with laser power of 3W and scanning speed of 1.0mm/s,a single channel groove with a width of 100μm and a depth of 78μm was realized.Multi-channel composite hydrophobic surface microstructure was fabricated directly with the coordination of the control system.In addition,residues accumulated in the ablated grooves,which may be the depolymerized MMA monomers.3.The intrinsic contact angle between PMMA surface and water was measured by contact angle measuring instrument.Based on Wenzel’s and Cassie’s wetting model,the relationship between the shape and size parameters of the microstructures and their hydrophobic properties was analyzed,and then the first-order microstructures on PMMA surface were constructed.To enhance the strength of microstructures and faciliate fabrication,a variety of multistage microstructures were designed to further improve hydrophobicity.4.Based on the designed microstructures,femtosecond laser direct writing technique was adopted to provide guidance on the processing of microstructures on PMMA surface,and the relationship between various microstructures and their hydrophobic properties was tested.The experimental results showed that microstructures were prepared on PMMA surface by using femtosecond laser,so that the PMMA surface could be transformed from hydrophilic to hydrophobic.In particular,the maximum contact angle of the second-order microstructures was more than 152°,achieving the superhydrophobic function.The results of hydrophobicity test for various microstructures were consistent with the design values,which indicates the reasonability of the design theory.