| Polymer polytetrafluoroethylene(PTFE)has a broad application prospect in such areas as high frequency electronics,oil-water separation and self-cleaning because of its excellent electrical,thermal,and chemical stability.Whereas,its extremely low surface energy and poor adhesion to other materials greatly limit its wide applications.Laser surface modification has been widely applied in the changes of chemical and/or physical properties of a material due to its high region selection,efficiency,and flexibility.However,the current research on PTFE laser modification is mainly focused on the use of ultra-short pulse width(e.g.,femtosecond)and short wavelength(≤300 nm)laser.Because of their lower cost and easy maintenance,picosecond(ps)and ns(ns)lasers have gained wide applications.Nevertheless,there are relatively few studies on ps or ns laser surface modification and application of PTFE material,and especially,the surface wettability variation regularity of PTFE after ps or ns laser modification has not been reported.Basing on these,the effects of ps or ns laser modification on PTFE surface wettability variation and the application of oil-water separation,self-cleaning,and metal layer adhesion strength were systematically studied,and the corresponding regularity and mechanism were explored in detail.The main results and conclusions were listed as follows.(1)In the mode of single pulse and parallel line scanning,the ablation mechanisms of PTFE by ps or ns laser(i.e.,ps infrared(IR)laser,ps ultraviolet(UV)laser,and ns UV laser)were investigated.Depending on the analysis of surface micromorphologies,for the first time,it was proposed that the mechanism of the ps IR pulse laser(1064nm)ablation on PTFE were dominated by photothermal effect.The ps UV pulse laser(355nm)ablation was governed by photochemical effect,while the ns UV pulse laser(355nm)ablation was dominated by photothermal and photochemical synergetic effect.(2)In the modes of grid scanning and parallel line scanning,the effects of different laser modifications on the PTFE surface wettability variation were explored in detail.In the grid scanning mode,the wettability of the PTFE surface ablated by different laser showed a similar change trend when the single laser processing parameters changed.This was due to the similar morphology evolution of the laser-modified surface.More importantly,the superhydrophobicity with accurately and continuously tunable water adhesion(i.e.,about 2° to about 90° sliding angles of the water droplets on these surfaces)could be constructed on the surface of PTFE,polydimethylsiloxane(PDMS),and polyvinylidene fluoride(PVDF)by changing laser scanning interval.Therefore,this was a versatile fabrication method.In the parallel line scanning model,the superhydrophobic PTFE surface with anisotropic wettability could also be fabricated by simply changing the laser scanning interval.The water anisotropic sliding angles on PTFE surface fabricated by ps UV laser were able to reach 17.5°,which was bigger than that of ps infrared IR laser(14.6°)and ns UV laser(11.8°).(3)To expand the application range of PTFE polymer,after laser surface modification,the application of PTFE in oil-water separation and self-cleaning were suggested.The results showed that the oil-water separation efficiency of PTFE membrane could be effectively controlled and tuned by the precise fabrication of surface micromorphology and micropore diameter.When the micropore size of the membranes was less than ca.180 μm(here,the surface roughness Ra was 5.8 μm)or when the surface roughness Ra was more than 4.9 μm(here,the micropore size of PTFE membrane was 180 μm),the excellent separation efficiencies of above 98.0% could be obtained for different oil-water mixtures.Furthermore,the separation efficiencies showed no obvious change(i.e.,>98.0%)after suffering heavy erosion or after 40 separation cycles,indicating that the membranes had excellent stability and applicability.At the same time,the results of surface self-cleaning experiments showed that the as-prepared superhydrophobic PTFE material had good surface self-cleaning ability.When the process of coalescence-induced rebound of two equivalent-volume droplets was simulated by ANSYS software,the simulation accuracy was more than 90%.This indicated that the simulation model had high reliability.(4)To solve the problem of poor adhesion strength between the PTFE surface and copper layer.The effect of different laser processing parameters on the adhesion was studied.The results showed that,after ps UV laser ablation,the PTFE surface had the highest adhesion strength(about 6.8 MPa,2-3 times as much as that reported in the existing literatures,compared with ps IR laser and ns UV laser).Next,using response surface analysis(RSA)method,the effects of ps UV laser processing parameters on the adhesion strength were investigated,and the mathematical model between the adhesion strength and laser parameters was established.The results showed that the error between the actual and predicted adhesion strength of the model was less than 10%.It indicated that the mathematical model had high reliability.In summary,the systematical studies on the effects of ps and ns laser modification on PTFE surface morphology,chemical composition,wettability,adhesion strength,and application,not only deepened and enriched laser-PTFE interaction theoretical system,but also effectively broadened the PTFE practical application range. |
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