Glass Surfaces: Experimental Study and Computer Simulation

该项目的目标是更好地了解多组分硅酸盐玻璃表面的分子结构，特别是改性离子对表面吸附位点分布和活性的影响。提出了一项多组分硅酸盐玻璃表面的协调研究，其中计算机模拟和实验研究将针对原子/分子尺度表面结构的吸附等温线的表征和预测。硅基玻璃的原子结构的计算机模拟是基于一种新的方法来模拟玻璃二氧化硅表面。假定纯玻璃二氧化硅的表面是疏水的。为了在计算机模拟中实现这一点，有必要使结构松弛时间在计算机模拟的时间限制内。鉴于以前的玻璃计算机模拟集中在通过一些退火突然去除周期性边界条件而产生的理想表面上，本研究将更具体地关注表面的退火，以努力模拟较低能量的熔融表面。一种新的实验方法将用于确定等温线和吸附能在玻璃粉末，玻璃纤维和凝胶。这种方法是比较方法的延伸，其中吸附剂（具有未知吸附特性）的气体吸附等温线与标准（参考物质）的等温线相对应。等温线将与计算机模拟的等温线进行比较，以获得(i)多组分玻璃表面原子结构的详细描述，（ii）与改性剂、非桥接氧或表面硅烷醇相关的局部电场，（iii）表面改性阳离子的空间分布以及（iv）水（和其他活性物质）在这些非均质表面上的吸附机制。静态sim S、FTIR和相关光谱技术将进一步验证表面组成效应和不可逆化学吸附反应。使用计算机方法精确模拟玻璃表面和物理吸附等温线的能力为预测新玻璃成分的表面热力学性质和/或解释现有玻璃和玻璃产品的吸附行为提供了强大的工具。二氧化硅和硅酸盐玻璃的表面和表面化学是其许多特性的基础，包括强度、腐蚀性、聚合物粘附性、生物反应性和光学响应。该项目是通过模拟和研究模型非晶表面上简单气体吸附理论的科学家与那些专注于表征和处理更复杂玻璃表面的科学家合作进行的。＊＊＊

9803884 Pantano The goal of this project is to gain a better understanding of the molecular structure of multicomponent silicate glass surfaces, and especially, the effect of modifier-ions upon the distribution and activity of surface adsorption sites. A coordinated study of multicomponent silicate glass surfaces is proposed in which computer simulation and experimental studies will be directed toward characterization and prediction of adsorption isotherms in terms of the atomic/molecular scale surface structure. The computer simulation of the atomic structure of the silicate-based glasses is based on a novel approach to the simulation of the vitreous silica surfaces. It is assumed that the surface of pure vitreous silica should be hydrophobic. To achieve this in a computer simulation, it is necessary to bring the structural relaxation time within the time limits of computer simulation. Whereas previous computer simulations of glass have focused on the ideal surface created by abrupt removal of periodic boundary conditions with some annealing, this study will focus more specifically on the annealing of surfaces in an effort to simulate lower energy melt surfaces. A novel experimental approach will be used for determining the isotherms and energies of adsorption on glass powders, glass fibers and gels. This approach is an extension of the comparison method in which the gas-adsorption isotherm of an adsorbent (with unknown adsorption characteristics) is plotted against the standard isotherm (of a reference material). The isotherms will be compared with computer simulated isotherms to obtain (i) detailed descriptions of the atomic structure of multicomponent glass surfaces, (ii) the local electric fields associated with modifiers, non-bridging oxygens or surface silanols, (iii) the spatial distributions of modifying cations on the surface and (iv) the mechanism of water (and other reactive specie) adsorption on these heterogeneous surfaces. Static-SIM S, FTIR and related spectroscopic techniques will be employed to further validate surface composition effects and irreversible chemisorption reactions. %%% The ability to accurately simulate the glass surface and physisorption isotherms using computer methods provides a powerful tool to predict the surface thermodynamic properties for new glass compositions, and/or to interpret the adsorption behavior of existing glasses and glass products. The surface and surface chemistry of silica and silicate glasses are fundamental to many of their properties including strength, corrosion, polymer adhesion, bioreactivity, and optical response. The project is being carried-out through the collaboration of scientists simulating and studying the theory of simple gas adsorption on model amorphous surfaces with those whose focus is characterization and processing of more complex glass surfaces. ***