介面單分子層聚苯乙烯和頻光譜的理論探討

Abstract

和頻光譜儀(Sum frequency generation spectroscopy)於探究介面結構之實驗是一個功能強大的方法，並已有數種計算方法被研發成功。 但截至目前為止，聚合物受介面吸附位向與角度方向所導致光譜改變情況之研究尚未被系統性討論。

本研究中，我們將關注頗受流行的聚合物分子-聚苯乙烯（PS）於密度泛函理論下探討單層聚合物之單共振型態和頻光譜，其光譜擬合範圍著重於苯環上的碳氫原子振動模式。 首先述說空氣環境中改變分子及接觸面之夾角大小是否對光譜強度造成影響，亦能佐證實驗光譜並告知正確的表面接觸角度。 再者，我們將探討聚苯乙烯於六角晶體石墨上的數種優化幾何構形與化學吸附能量，此結果有助於了解有效的局部穩定位置。

Sum frequency generation (SFG) spectroscopy is a powerful experimental technique capable of probing interfacial structures. In theoretical calculation, more molecular theory for various kinds of SFG has been developed. However, up to this date, for the polymers’ interface adsorption sites and the degree of orientation affect SFG peak which has never been systematic treatments.

In this present study, it is fitting for us to discussion the popular polymer compound, polystyrene (PS). Report the theoretical mode of density functional theory of IR-UV/Vis SFG with IR-resonance for monolayer PS. The spectrum focus in the CH stretching mode region of benzene ring is simulated and first is carried out on the SFG intensity dependence of the angles between aromatic rings and principal axis at monolayer PS /air. This enables us to understand the correct angle for experimental observations. Next, we shall optimized geometries and chemisorptions energies for monolayer PS on more adsorption sites, namely hexagonal crystal graphite. It is indicated that the stable effective adsorption sites for local minimum.