Infrared Spectroscopic Characterization by Atomic Force Microscopy of Two Model Nano-Samples of Low-Density Polyethylene Designed by Laser Ablation and Ultraviolet/Ultrasound

• Two types of low-density polyethylene nano samples were designed to mimic environmental nanoparticles. • Local infrared spectra of particles at the molecular order were successfully obtained. • It will be possible to discuss biotoxicity testing focusing on the surface chemical state of particles floating in the environment. Model plastic samples mimicking the behavior of environmental nanoparticles (NPs) are necessary for understanding their biological effects. This is because the particle size and surface chemistry of plastic particles can be parameters for biotoxicity testing. Therefore, different types of particles need to be produced or designed. In this study, the chemical and physical properties of two model nano-samples of Low-Density Polyethylene (LDPE) were investigated; one designed by nanosecond laser ablation (LASER-LDPE.NPs), and the other designed by a combination of Ultraviolet (UV) irradiation and Ultrasound (US) exposure (UV/US-LDPE.NPs). AFM-IR, for detecting and imaging the response of a sample by scanning an AFM cantilever while irradiating an IR laser, was used to analyze the local chemical properties of these particles. New peaks specific to oxidation and degradation reactions were observed. In addition, the LASER-LDPE.NPs tend to have greater oxidation behavior with increasing methyl groups and a greater degradation with increasing carbonyl index than UV/US-LDPE.NPs. It was found that each NP production process produces NPs with unique chemical and physical properties. These designed model plastic particles mimic NPs in the environment and a study of their respective oxidation and degradation properties is expected to provide new insights into the assessment of biological effects. (200 words)