New Strategy to Achieve Laser Direct Writing of Polymers: Fabrication of the Color-Changing Microcapsule with a Core-Shell Structure.

This paper proposed an efficient and environmentally friendly strategy to prepare a new color-changing microcapsule with a core-shell structure for laser direct writing of polymers, and only the physical melt blending of polymers was employed. The laser absorber (SnO2) and the easily carbonized polymer (PC) were designed as the "core" and the "shell" of the microcapsule, respectively. The microcapsules were in situ formed during melt blending. Scanning electron microscopy, transmission electron microscopy, and energy-dispersive spectrometry confirmed the successful preparation of SnO2/PC microcapsules with a core-shell structure. Their average diameter was 2.2 μm, and the "shell" thickness was 0.21-0.24 μm. As expected, these SnO2/PC microcapsules endowed polymers with an outstanding performance of near-infrared (NIR) laser direct writing. Raman spectroscopy and X-ray photoelectron spectroscopy indicated that the color change was ascribed to the polymer carbonization because of the instantaneous high temperature caused by the SnO2 absorption of NIR laser energy. Optical microscopy observed a thick carbonization layer of 234 μm. Moreover, Raman depth imaging revealed the carbonization distribution, confirming that the amorphous carbon produced by the carbonization of the PC "shell" is the key factor of SnO2/PC microcapsules to provide polymers an outstanding performance of laser direct writing. This color-changing microcapsule has no selectivity to polymers because of providing a black color source (the carbonization of PC) itself, ensuring the high contrast and precision of patterns or texts after laser direct writing for all general-purpose polymers. We believe that this novel strategy to achieve laser direct writing of polymers will have broad application prospects.