Underwater Laser Treatment of PET: Effect of Processing Parameters on Surface Morphology and Chemistry

Rapid development of nanotechnology in processes of metal nanoparticle immobilization on solid surfaces, especially polymeric ones, requires the study of particular issues within these complex approaches. Numerous studies have been published on laser light mediated manipulation with single metal nanoparticles in water environment and even laser assisted immobilization of such particles on polymeric substrate, however, not much has been reported on fundamentals of underwater laser processing of polymer itself, especially regarding to resulting surface morphology and chemistry. In this work, we study surface morphology (atomic force microscopy (AFM)) and chemistry (angle-resolved X-ray photoelectron spectroscopy (ARXPS) and inductively coupled plasma-mass spectroscopy (ICP-MS)) of polyethylene terephthalate (PET) after underwater laser treatment in broad scale of applied laser fluencies and operating voltages. Due to typical dependence of laser efficiency on operating voltage, induced nanostructures on PET exhibited a noticeable symmetry spread out around the maxima of laser efficiency for low laser fluencies. The study of surface chemistry revealed that at high laser fluencies, photochemical decomposition of macromolecular polymer structure took place, resulting in rapid material ablation and in balanced chemical composition of the surface throughout the studied profile. Enrichment of the water bath by the low-molecular polymer degradation products proves that ablation mechanism is the governing process of surface nanostructure formation in underwater laser processing.