奈米碳管複合材料之機械性質研究

Abstract

由於奈米碳管有極佳之機械性質、導電性及熱傳導性，因此它們有極佳的潛能應用於各種領域。本論文主要分為三個章節探討奈米碳管之分散性、增強子性能(reinforcing effect)及Halpin-Tsai理論分析。 第一部分為奈米碳管懸浮於有機溶劑之分散性研究，奈米碳管如欲有預期之表現，則其應能均勻的分佈於分散劑中，且不會糾結成一團。我們以Hansen Solubility parameter ( )來探討奈米碳管在各種有機及水溶劑中之分散情況，如果溶劑中含較少之極性及氫鍵物質，奈米碳管在此溶劑中可形成較佳分散性，分性因子( )也影響了奈米碳管的分散性。 第二部分為奈米碳管添加於壓克力母材之機械性能增強研究，奈米碳管以直接添加法輔以超音波震盪之方式直接添加於壓克力凝膠中，由電子顯微鏡觀察，奈米碳管可均勻的分佈於壓克力母材中，良好的分散性可促使碳管充分發揮其增強子之功能，然而分散性若不佳，則複合材料之機械性能不易提升。溶劑分散效應及分子間吸附力，例如凡得瓦爾力亦影響奈米碳管於基材中之分散性，奈米碳管經酸處理後所生成之羰基亦能幫助母材分子與碳管分子形成共價相連。奈米碳管與高分子間之作用機制極其複雜，尤其是受到介面反應的影響。我們以奈米壓痕機及拉伸試驗測試複合材料之機械性質，結果顯示當奈米碳管之濃度增加，複合材料之機械性能亦跟著增加。 第三部分，修改過之Halpin-Tsai理論被用來預測奈米碳管/壓力克複合材料之機械特性。由於壓克力分子大小和奈米碳管相當，二者之分子作用機制受到區域分子結構(local molecular structure)，及鍵結形式的影響，我們假設碳管及母材之分子為連續材料，利用修飾後之Halpin-Tsai理論可探討碳管的長度變化、體積比、定向性(orientation)及不同直徑分佈對複合材料之增強性影響。奈米碳管的直徑分佈影響了複合材料之機械性能表現，直徑較大之碳管，其應變能會較低，導致其複合材料之機械強度不似直徑較小之碳管強，由實驗所得到之楊氏係數與理論值有相吻合之結果。

Because of their superior mechanical strength, electrical conductivity, and thermal conductivity, carbon nanotubes (CNTs) had enormous potential in many technical applications. This study discussed the solvent dispersion, reinforcing effect, and modeling characterization of carbon nanotubes in PMMA matrix. It was divided into three sections. In the first section, the dispersion state of CNTs in various solvent is discussed. For optimal performance in many applications, CNTs should be separated into individual tubes. Dispersion of CNTs in various organic or aqueous solvent is studied to correlate the degree of dispersion properties with Hansen Solubility parameter. If the solvent contains less polar or hydrogen-bond containment, the nanotubes show well dispersed properties. The dispersion state is also affected by the dispersion component. In the second section, CNTs were dispersed into PMMA gel to enhance its mechanical strength. CNTs/PMMA composite films were fabricated using direct mixing and sonication. Most of the CNTs were dispersed uniformly. The effective dispersion of CNTs improves the mechanical performance of the composite film, while the poor dispersion reduces the performance. The solvent solubility and attractive intermolecular forces, such as hydrogen bonds and Van Der Waal forces affect the dispersion of the carbon nanotubes. The carbonyl group contributed to the formation of a covalent bond between PMMA and CNTs molecular. The mechanical interaction between carbon nanotubes and the polymer was very complex. It was also governed by the interface interaction. The mechanical properties were test by a nanoindenter system and a tensile test. The mechanical properties of the composite films improved as the concentration of carbon nanotubes increased. In the third section, a modified Halpin-Tsai theory is presented for developing CNTs/PMMA composite models. Because PMMA molecules are on the same size as the nanotubes, the interaction at the PMMA/nanotubes is highly dependent on the local molecular structure and bonding. The models assume that the tubes and matrix are continuous materials. The fundamental understanding of the length effect, volume fraction, orientation and diameter distributions of CNTs were taken into account the predicted strength of composite materials. The composite elastic properties are sensitive to the nanotube diameter, because larger-diameter nanotubes have lower strain energy and showed less effective when relative to small-diameter nanotubes. The correlation of the experimentally obtained Young’s modulus was compared to the modified Halpin-Tsai theory, and they showed a corresponding result.