The effects of temperature and humidity on the optical properties of PMMA: A hybrid first principle calculation and molecular dynamic simulation

Polymethyl Methacrylate (PMMA) is an important macromolecule material with high plasticity, which is also widely used in the manufacturing of LED diffusion plates, because it has several advantages, such as excellent optical transparency, chemical stability, good weather resistance, radiation resistance and surface hardness (no scratch). It also can be completely recycled and easy processing. However, there are a few papers that have reported the changes in the optical properties of these materials affected by the environmental factors like humility and temperature. In this paper, we study the optical properties of the PMMA material in the humidity environment in the light of the PMMA material of high power LED lighting. The simulations were performed using Materials Studio software to investigate and analyze the influence of material structure on the optical properties in the different humidity and temperature environments. First of all, the molecular structure model of PMMA was optimized by Dmol3 function, and the molecular dynamic simulations were carried out using the Forcite package with the time step and total simulation time set to be 1.0 fs and 50 Ps, respectively. Subsequently, the optical properties of the PMMA under different conditions were calculated by utilizing the Castep package. The presence of oxygen would have apparent influence on the electronic and optical properties of the PMMA. Specifically, the visible light reflectivity and absorption are enhanced with the attachment of oxygen molecules.