Surface modification of bisphenol A polycarbonate using an ultraviolet laser with high-speed, direct-writing technology

The direct-writing surface modification of black bisphenol A polycarbonate (BAPC) was achieved at high laser scanning speeds of 600–1000 mm·s− 1 using a 355 nm-wavelength, all-solid state, Q-switched, high-average power, nanosecond-pulse width laser. Compared with the widely reported surface modification technologies (e.g., femtosecond laser irradiation and excimer laser irradiation), this modification was low-cost, efficient, flexible, and with great industrialization potential. During the modification, it was found that laser fluence and pulse width were able to significantly affect the water contact angle, wetting behavior, microstructure, roughness, and chemical composition of the surface. When the applied laser fluences were low (i.e., less than the critical fluence of the ultraviolet laser direct-writing surface modification on the BAPC material), the water contact angle tended to decrease, the hydrophilicity was slightly improved, the relative content of the oxygen-containing groups (e.g., CO and COO−) increased, the microstructure and roughness only showed a slight change, and the wetting behavior was consistent with Wenzelʹs law. On the other hand, when the applied laser fluences were high, the water contact angle increased, the hydrophilicity decreased, and the relative content of the oxygen-containing groups also increased. Here, a porous microstructure with periodical V-type grooves was generated and the roughness obviously increased. In this case, the wetting behavior could be explained by the Cassie–Baxter model, i.e., the microstructure and roughness change played a deciding role. It was possible that different laser parameters resulted in different material deformations and removal processes, thereby resulting in different surface chemical compositions, microstructures, roughnesses, and wetting properties.