No abstract

Silicate glasses have evolved from basic structural materials to enabling materials for advanced applications. In this article, we unravel the origin of the mixed alkali effect for alkali silicate 22.7R 2 O-77.3SiO 2 glasses (R = Na and/or K) by identifying the variation in the alkali ion location around the non-bridging oxygen atoms. To do so, we constructed a state-of-the art structural model, which reproduces both diffraction and NMR data with a particular focus on the behavior of the alkali ions. A novel topological analysis using persistent homology found that sodium-potassium silicate glass shows a significant reduction in large cavities as a result of the mixed alkali effect. Furthermore, a highly correlated pair arrangement between sodium and potassium ions around non-bridging oxygen atoms was identified. The potassium ions can be trapped in K-O polyhedra due to the increased bridging oxygen coordination; therefore, the correlated pair arrangement is likely the intrinsic origin of the mixed alkali effect.

An investigation of the excited state processes in a three‐component initiating system based on a new ketone/amine/onium salt combination has been carried out for the first time. The results obtained through time‐resolved laser spectroscopy and the data gained in radical photopolymerization experiments suggest that the addition of an onium salt to the usual ketone/amine system mostly result in a decrease of the termination reaction of the growing macromolecular chains, thus allowing an increase of the rate of polymerization. © 1993 John Wiley & Sons, Inc.

The excited state interactions occurring when a three‐component system of thioxanthene derived dye TXD/amine/additive (diphenyliodonium salt, CBr4, benzoyl peroxide, cumene hydroperoxide) is subjected to sensitization processes in the visible range, were investigated through time‐resolved absorption spectroscopy, spectrofluorometry, and photolysis. The rate constants of the various operative processes were measured together with the values of the fluorescence quantum yields (e.g. ϕ f = 0.75 ± 0.07 in methanol) and the lifetimes of the singlet excited state of the dye (e.g. 6 ns in methanol). Singlet state quenching by methyldiethanolamine (MDEA) occurs with a rate constant k = 109 M−1 s−1 in methanol. The reactivity of the triplet excited state of the dye is very low (k = 5.6 × 104 M−1s−1 for the TXD/MDEA interaction). The ketyl radicals that arise from the interaction of the singlet state of the dye with the amine, are quenched by such additives as CBr4 (k = 6.7 × 105M−1s−1), or the onium salts (k = 5.7 × 105M−1 s−1). The calculations of the yields of interaction of the singlet state of the dye with the two components of the system demonstrate that the process of quenching by the amine is the main one (ϕint = 0.5) compared to that by, e.g., an onium salt (ϕint = 0.07). Sensitivity of 0.3 mJ cm−2 obtained in a laser scanning system is also reported. © 1996 John Wiley & Sons, Inc.

Atomistic computer simulations can provide insights into silicate glass‐environment interactions with the recent development of reactive potentials. However, the accuracy of generated glass structures with these potential was usually not fully examined. In this paper, the capability of the reactive force field (ReaxFF) to describe the short and medium range structure features of sodium silicate glasses in molecular dynamics simulations is investigated by comparing a widely used partial charge pairwise potential and available experimental data. Glass structure information such as pair distribution function (PDF), coordination number, Qn species, neutron broadened structure factor, and X‐ray broadened structure factor of the glass structures from ReaxFF simulations were calculated and compared to evaluate the generated glass structure. Advantages and limitations of the potentials and glass forming procedures, as well as areas of further improvement, were discussed. The results show that the recently refined ReaxFF parameters through the proposed procedure enable the simulations of sodium silicate glass structures with minimal defects, which paves the way to investigate water‐glass interaction mechanisms with the reactive enabled potentials.