Surface Chemical Transformations of UV Irradiated Silica-Epoxy Nanocomposites

J.M. Gorham, T. Nguyen, C. Bernard, D. Stanley, R.D. Holbrook
National Institute of Standards and Technology, US

Keywords: nanoparticle release, EHS


Silica nanoparticles (SiNPs) incorporated into a polymeric matrix, or silica nanocomposites (NCs), are used in a wide variety of commercially available products in numerous natural and artificial environments. Environmental factors, such as ultraviolet (UV) light, may modify the SiNCs during their lifetime of service, giving rise to the possibility of degradation leading to nanoparticle (NP) release. Ultimately, light-induced modifications are most likely to occur at the SiNC-gas interface, which suggests that surface transformations will play a major role in the potential release of SiNPs throughout the lifecycle of this material. To better understand these surface transformations, we investigated the impact of high intensity simulated solar radiation (290 nm – 400 nm) to the surface and bulk properties of SiNCs, which have exhibited NP release in other studies [1, 2]. Surface spectroscopic analysis (XPS/ATR-IR) in conjunction with elemental analysis (EDS) was employed to understand the chemical transformations that occur as a result of UV-aging of SiNCs. Further analysis using microscopy (AFM/SEM) revealed physical transformations present at or near the surface including increased roughness and cracking with increased UV-aging. Results demonstrate that UV-induced transformations of SiNCs occurred via photo-oxidation of the epoxy matrix resulting in a subsequent loss of polymeric material, surface enhancement of nanosilica concentration and increased surface roughness [2, 3]. Additional studies may include the impact of changing SiNP surface chemistry with silanes and detection of other nanofillers within an epoxy matrix.