運用分子模擬探討二氧化矽與有機-無機混成矽酸鹽玻璃材料之結構與基本性質

Abstract

本研究結合古典力場方法與分子動態模擬建立一套能夠有效建立有機矽酸鹽玻璃模型的計算程序。藉由此程序，我們得以建構不同尺寸、密度、網狀聯結度、或帶有不同末端基之非晶質二氧化矽與有機矽酸鹽玻璃材料之原子模型。經由本程序建立之非晶質二氧化矽，其結構特徵與前人文獻中使用其他方法產生之原子模型相符，證明此程序之合理性。 根據我們對建構出之有機矽酸鹽模型的計算結果發現，pcff力場模型對性質之預測與第一原理計算的結果相近。從機械性質的分析中我們推測：有機矽酸鹽系統之剛性未必隨含碳量增加而上升；在介電性質方面，我們認為雖然於結構中加入碳原子可降低系統內之離子極化程度，但同時也使電子極化程度增加，因此碳原子的取代未必能如前人所述般有效地提升系統之剛性並降低系統介電常數。此外我們也發現，系統之機械強度會隨孔隙率增加而下降，而在有機矽酸鹽玻璃材料內之孔隙率會受到結構內部末端基種類的影響。我們預測，若使用多孔非晶質二氧化矽作為絕緣層材料，其介電常數之下限約為1.7。

In this thesis, we combined classical force field methods and molecular dynamics simulations to establish an effective organosilicate glasses (OSGs) models developing process. By this procedure, amorphous silica and OSGs with various sizes, density, or with different terminal groups could be constructed. The structural characteristic of amorphous silica generated by this procedure is consistent with those generated by other methods in previous literatures, which proved the reliability of the procedure. According to our calculation, the properties of amorphous silica and OSG can be well-predicted by pcff force field since the results were strongly consistent with those calculated by first-principles calculations. From the analysis of mechanical properties of OSGs, we found that the mechanical strength may not be enhanced by adding carbon-bridged, which contradicted to the results in previous studies. From the analysis of dielectric properties of OSGs, we found that adding carbon-bridged decreased the ionic polarization of OSGs. However, the dielectric constant might not be reduced because it increased the electronic polarization at the same time. In addition, we found that the mechanical strength of materials would decrease with the increasing porosity and that porosity would be influenced by the type of terminal groups of OSGs. In our prediction, as insulator materials, the limit of the dielectric constant of amorphous silica should be around 1.7.