Triboelectric properties of calcium aluminosilicate glass surfaces

Recent experiments on flat, multicomponent glass surfaces have suggested that a particular surface's propensity to adsorb water plays a critical role in how that surface accumulates/dissipates electrical charge. A key driver for glass surface-water reactivity may be structural defect concentration(s) at the surface, which can be largely influenced by bulk composition. To further explore these hypotheses, a series of ternary calcium aluminosilicate (CAS) glasses along the charge-balanced join were modeled using classical molecular dynamics (MD), with the goal of understanding how glass composition impacts structural defect concentrations (NBO, under-coordinated Si, Al, etc.) in the outermost layers (similar to 5 angstrom) of the surface. Concurrently, CAS glasses with the same compositions were prepared in the laboratory and their surfaces analyzed for charge response at variable humidity using a rolling sphere test (RST), as well as a newly developed metrology for contact charging phenomena called an electrostatic gauge (ESG). Molecular water interactions with CAS fracture surfaces were studied using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) to establish correlation between bulk and surface compositional trends. Experimental results, in conjunction with corresponding MD calculations, suggest that glass bulk chemistry along with resultant surface defect states (NBO, etc.) represent crucial driving factors in glass contact charging.