| Summary: | 碩士 === 國立中山大學 === 材料科學研究所 === 90 === Abstract
Organically modified montmorillonite by a long chain alkylammonium surfactant was used to prepare polyimide/clay nanocomposites in this study. Several attempts were made in an effort to achieve fully exfoliated nanocomposites. These included the one-step method, two-step method and in-situ polymerization method. At the same time, the effects of polyimide structures and clay contents were studied. Two dianhydrides and two diamines were used to prepare polyimide/clay nanocomposites via the two-step method. The polyimide/clay nanocomposites with various clay contents from 1.5 ~ 10 wt % were prepared via the two-step method too. The structure of polyimides and the dispersion level of clay were identified by Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometry (XRD). Thermogravimetric analysis (TGA) was performed to demonstrate the thermal stability of the nanocomposites.
TGA and XRD results indicate the surfactants are intercalated into the layers of clay. FTIR results indicate the all polyimides in the nanocomposites are formed successfully. XRD results indicate the BPDA-ODA/clay nanocomposite within 3 % by weight of clay via the two-step method is shown to have the best dispersion level of clay. These results are consistent with observations from TGA. The temperature at 10 % by weight loss of the nanocomposite is 31 ℃ greater than that of pure BPDA-ODA. The formation mechanism of polyimide/clay nanocomposites via the two-step method can be described by three distinct steps. A polyamic acid/clay mixture with an exfoliated morphology is first formed. A portion of solvents and intercalated surfactants are then either degraded or expelled from the clay gallery under thermal imidization, resulting in a reduced gallery height of 1.32 nm. On the other hand, portion of the clay layers show an exfoliated morphology due to the effective surfactant and polyimide molecules. As a result, a partially exfoliated polyimide/clay nanocomposite is obtained.
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