Neutron Compton scattering and transmission as probes of surface hydroxyl group dynamics in glasses.

Metal-oxide glass surfaces, such as silica-based and mixed oxides, often exhibit hydroxyl (–OH) terminations under ambient or water-rich conditions. These groups influence adhesion, catalysis, and functionalization by enabling hydrogen bonding and providing sites for covalent coupling agents. Despite extensive study, questions persist about the chemical dynamics of surface hydroxyls in disordered systems, especially regarding anharmonic and quantum effects often overlooked in ab initio models. We will use neutron Compton scattering (NCS) and neutron transmission (NT) to probe the nuclear dynamics of surface –OH protons in Li2O, B2O3, 40Li2O–60B2O3, and 10Li2O–90B2O3. Our initial data show that NCS and NT are sensitive to native –OH concentrations on the surface of Li2O, B2O3, 40Li2O–60B2O3, and 10Li2O–90B2O3. Samples will be heated at 100–550°C to vary –OH content, then cooled to room temperature for measurements. NCS will provide nuclear kinetic energies of Li, B, O, and hydrogen, while NT will yield total cross-section curves reflecting vibrational dynamics. We will complement density functional theory with molecular dynamics, using a neural-network-derived potential in DeePMD. Together, these experiments and computations will clarify the often overlooked quantum effects of surface hydroxyls.