利用多尺度模擬探討奈米複合材料之機械性質

Abstract

本研究目的是為了表現在聚亞醯胺基材添加二氧化矽奈米顆粒之奈米複合材料的機械性質，於提出連體微觀力學模型。藉由分子動力學建立並且模擬奈米複合材料，可以在奈米等尺寸的內含物以及周遭的基材部分之間發現凡得瓦間距以及非鍵結能量，而正交化非鍵結能量 (非鍵結能量除上內含物的表面積)和介面層的鍵結相關，考慮非鍵結間距即為介面層厚度，並且利用線彈簧模型模擬正交化的非鍵結能量進而計算出介面層的剛性，接著利用等效介面層模型，包括內含物，基材以及介面層，利用此模型模擬奈米複合材料的機械性質，將結果與分子動力學分析結果比較，利用等效介面層模型能夠準確的描述奈米複合材料的楊氏模數，另外研究也發現當顆粒大小降低時，奈米複合材料的楊氏模數會上升。

This research aims to propose a continuous micromechanical model for characterizing the mechanical properties of the nanocomposites containing silica nano-particles embedded in polyimide matrix. The molecular structure of the nanocomposites was established through molecular dynamic (MD) simulation, from which the non-bond gap as well as the non-bond energy between the nano-sized inclusion and the surrounding matrix was evaluated. It was postulated that the normalized non-bond energy (non-bond energy divided by surface area of the inclusion) is correlated with the interfacial interaction. Subsequently, a three phase micromechanical model including inclusion, matrix and effective interface was developed, in which the dimension of the effective interface was assumed equal to the non-bond gap and the corresponding stiffness was calculated from the normalized non-bond energy with the assistance of a linear spring model. Comparison of the results calculated from the micromechanical model and the MD simulation indicates that the three phase micromechanical model is capable of describing the Young’s modulus of particulate nanocomposites with accuracy. In addition, it was also found that with the reduction of the particulate size, the modulus of the nanocomposites become increasing.