Pitaya-Structured Microspheres with Dual Laser Wavelength Responses for Polymer Laser Direct Writing

A unique pitaya-structured graphene/TiO₂@PS microsphere with dual laser wavelength responses is designed and prepared via a facile approach of polymer melt blending. The graphene/TiO₂ particles ("pitaya seeds") are homogeneously distributed in the polystyrene ("pitaya pulp") of the microspheres with an average size of 1.5 μm. The graphene in microspheres serves not only as a laser absorber that has responses to both 355 nm UV and 1064 nm NIR lasers but also as a reducing agent of TiO₂ during laser direct writing (LDW). As expected, benefiting from the unique pitaya-structured structure, the graphene/TiO₂@PS microsphere can remarkably improve the performance of both NIR and UV LDW of polymers. The results of characterizations reveal that the black color caused by NIR LDW is due to the generation of the amorphous carbon and the color change after UV LDW is owing to the formation of black sp/sp² carbon compounds. Meanwhile, some TiO₂ in microspheres is reduced into the black/gray titanium oxides of Ti²⁺ and Ti³⁺ after NIR and UV LDW, respectively. The above co-contribution endows the graphene/TiO₂@PS microspheres with an outstanding color-changing ability. This pitaya-structured microsphere will have a profound effect on polymers' laser direct writing.