In the IR spectra of the silica and silicate glasses, the shifts of the maximum intensity position of the m Si-O-Si,as band upon heating or applying mechanical stress could be attributed to changes in the distribution of bond parameters such as bond length and bond angle. Upon heating, isotropic expansion occurs and the density changes; upon applying mechanical stress, anisotropic strain is induced and a significant change in the Si-O-Si bond angle is observed. From molecular dynamics simulations of a silica glass, we show that the peak position shift correlates better with the asymmetric change in the Si-O bond length distribution, rather than the Si-O-Si bridge angle, the O-Si-O tetrahedral angle, or the density change. This new finding provides an insight into how and why the m Si-O-Si,as IR peak of soda lime silica (SLS) glass shifts upon chemical strengthening via ion exchange and thermal tempering.

This paper describes the optical principles of specular reflection (SR) and attenuated total reflection (ATR)-infrared (IR) spectroscopy, both of which are useful methods for glass surface analyses. It should be noted that the shape, position, and relative intensity of peaks in reflectance spectra vary drastically depending on the IR incidence angle as well as the probe method (SR vs. ATR). For example, in SR-IR analyses of soda lime glass, the Si-O-Si stretch band shows a blue-shift from its original position and a new peak grows at ~1200 cm-1 as the IR incidence angle increases. In contrast, the Si-O-Si stretch band appears be significantly red-shifted from its original position in the ATR-IR spectra of soda lime glass. SR-IR spectra of

It is generally well known that not only the sodium itself, but also the non-bridging oxygen (NBO) sites associated with sodium ions are largely responsible for the surface reactivity of soda-lime-silica (SLS) glass. Thermal poling can modify the distribution of sodium in the subsurface region. In this work, a commercial SLS float glass was thermally poled using nonblocking electrodes in air. The Na + -depleted anode surface and the Na + -gradient cathode surface were characterized using a variety of methods to find the compositional, structural and morphological effects of thermal poling. Of particular significance is the use of nondestructive vibrational spectroscopy methods, which can lead to new and improved understanding of water interactions with sodium and its sites in the glass. It was found that during thermal poling, the Na + -depleted glass network on the anode side undergoes condensation reactions of NBO sites accompanied by the increase in concentrations of silanol (SiOH) groups and molecular water species. In contrast, silanol and water species do not increase and the silicate network change is negligible in the Na + -gradient cathode side. Vibrational sum frequency generation (SFG) spectroscopy analysis revealed the difference in distributions of hydrous species in the Na + -depleted and Na + -gradient surfaces. The structural information of the thermally-poled surfaces provides critical insights needed to understand the mechanical and mechanochemical properties of the Na + -concentration modified SLS glass surfaces reported in the Part 2 companion paper.