The Effect Of Laser Surface Modification On The Surface Properties Of Bisphenol A Polycarbonate Materials

Thermoplastic polymer material polycarbonate (PC) has been used as a very importantengineering plastic because of its many excellent properties. However, due to its low surfaceenergy and high chemical stability, it has a poor surface adsorbability and adhesiveness toother films and coatings. This greatly limits its direct applications in some fields. Therefore,it is necessary to modify the PC surface and to improve its surface properties.In this work,355nm-wavelength ultraviolet (UV) nanosecond pulse laser modificationon the surface of bisphenol A polycarbonate (PC) coated with a film of water was suggested,and the effect of laser processing parameters on PC surface properties was explored. Itshowed that laser fluence and pulse frequency were the two more important parameters.Through analyses and measurements of scanning electronic microscopy, X-ray photoelectronspectroscopy, etc., the change of the surface microstructure, roughness, water contact angle,wettability, chemical composition, and surface energy before and after laser modificationwas investigated. It indicated that there existed a certain UV laser fluence threshold Fth,which was corresponding to a certain laser pulse frequency, respectively. When the laserfluences applied were less than Fth, the water contact angle had a decreasing tendency, thehydrophilicity was slightly improved, the relative content of oxygen-containing polar groups(e.g., O-C and C=O) increased, the microstructure and roughness only had a very slightchange, and the wetting behavior complied with the Wenzel law. On the other hand, whenthe laser fluences applied were larger than Fth, the porous microstructure with periodicalV-type groove generated, and the roughness had a significant increase. Here, the surface washydrophobic, and the wetting behavior could be explained by the Cassie model. Next,according to the van Oss acid–base theory, the surface energy was calculated by measuringthe contact angle of three liquids water, ethylene glycol and methylene iodide on themodified surface. It was found that the surface energy of the modified PC surface had asignificant increase. This would be very helpful to improve the adsorbability and adhesiveness.The adsorbability to metal (complex) ions on the modified PC surface was also studied.It showed that the region-selective adsorption of the metal (complex) ions on the surface wasfeasible, by combining the modification method with proper rinsing procedure. It testifiedthat the generation of the pourus, periodical groove microstructure and the relative contentincrease of the oxygen-containing polar groups were the main factors affecting theadsorption strength. At last, using magnetron sputtering technology, metallic copper layerwas deposited on the modified PC surface, and the adhesion strength between the copperlayer and the PC substrate could met the highest grade-5B, according to test method B of theAmerican Society for Testing and Materials standard D3359-08. Obviously, nanosecondpulse UV laser modification on the PC surface was feasible and promising.