• 作者： Yang, Yih-Pey; Hwang, Yug-Min; Tsay, Ruey-Yug
• 中文摘要： 本研究目的在於探討硬脂酸單分子膜在其膜壓高於平衡膜壓值時，所產生的崩塌現象。研究主要是以膜壓測定裝置量測單分子膜在固定膜壓下之分子表面積隨時間的變化，並利用Vollhardt等人所提出的成核模型進行模擬。我們使用非線性迴歸法取代原線性法而驗證了最終面積為一重要參數，只要微小的改變，就可求得不同成核機制，因此由原法所得之特定機制是不正確的。我們也利用穿透式電子顯微鏡來觀察崩塌微結構，其形呈不規則之多層塊狀，這與理論模型中所假設的成核機制完全不同。此結果顯示，成核形狀於理論模型中並不重要，這與先前理論模擬之結果相符，亦即我們無法只根據分子表面積的分析而得特定之機制。本研究並建立了一經驗式，由此式即可預測不同膜壓下之崩塌速率常數。
• 英文摘要： The objective of this research is to study the collapse mechanism of stearic acid monolayer at surface pressure beyond its equilibrium spreading pressure. A film balance system and a transmission electron microscope were utilized to investigate the constant surface pressure relaxation kinetics and the microstructures of the collapsed monolayer, respectively. And the nucleation-growth model proposed by Vollhardt et al. was applied to simulate the constant surface pressure relaxation behavior. By a non-linear regression method proposed herein, we confirmed that the final surface area is a sensitive parameter in determining the best fit value of time exponent, which represents a specific nucleation-growth mechanism, and the best fit value of time exponent claimed by Vollhardt et al. Utilizing a linear regression method is actually incorrect. Our electron microscopy observations illustrated that the collapse structure of stearic acid monolayer is terrace-like and irregular in shape. This result of morphological study implied that the geometric shape of the collapse structure is not an important factor in determining collapse rate. This statement correlates well to the fact disclosed by the present non-linear regression studies, i.e., there is no optimum value of time exponent can be determined by analyzing the relaxation data alone. In order to predict the overall transformation rate constant for a monolayer with various surface pressure, a simple empirical equation describing the relationship between rate constant and surface pressure of stearic acid films was also established for the case of time exponent equal to 2.0.
• 中文關鍵字： 脂肪酸; 界面; 崩塌
• 英文關鍵字： Fatty Acid; Interface; Collapse