- 學位論文
以陰離子和陽離子脫層蒙脫石製備離子液體複合材料之製程及阻抗分析
Processing of ionic liquid composite materials incorporating exfoliated montmorillonite prepared by anionic and cationic methods and their impedance analysis
摘要
本實驗室過去曾發現利用乳化聚合脫層的蒙脫石奈米片(exMMT)，由於帶負電可用來膠化1-methyl-3-propylimidazolium iodide (PMII)離子液體，使之具有不揮發不滲漏的優點，將之做成染料敏化太陽能電池的膠態離子液體電解質，結果不但不會降低光電轉化效率，效率反而由6%提昇到7.77%。因此本論文除了探討以陰離子脫層法製得之脫層蒙脫石結構與水溶液導電性質外，亦將合成帶陽離子胺鹽的長鏈分子來脫層蒙脫石，並與陰離子脫層法相互比較。除了利用TEM觀察脫層後之蒙脫石單片結構外，亦與AFM所測得的結果進行比較，結果顯示兩種方法脫層後之蒙脫石長寬均約300奈米，厚度則為1奈米。接著以XRD觀察脫層蒙脫石之回疊現象，並從TGA分析得知脫層劑之殘留量為12%，輔以理論計算得知蒙脫石奈米片回疊時，脫層劑附著於蒙脫石表面之傾斜角度為6度。除此之外，由於脫層劑的殘留，故其對蒙脫石上各金屬離子的影響也需要加以討論，以FT-IR觀察蒙脫石奈米片上的官能基特性峰，發現兩種方法的Si-O特性峰均有變寬的趨勢，表示蒙脫石有確實被脫層，而陰離子脫層法的Mg-O特性峰則有偏移的現象，表示結構上受到脫層劑之影響而改變。以XPS討論蒙脫石上金屬離子鍵結能的變化時，亦發現陰離子脫層法的Mg1s軌域特性峰往低能量處偏移，陽離子脫層法則是Si、Al、Mg均受到影響，證明了脫層劑殘留於蒙脫石上的事實。之後，我們探討不同脫層方法之exMMT/PMII電化學性質，以EIS測量R2值隨蒙脫石含量的變化，發現其於膠化點附近有下降的趨勢，此現象若用Raman光譜與XPS來分析，則可能是由於碘離子被氧化為I3-或I5-所致。最後在exMMT/PMII中添加不同含量的碘，由EIS結果顯示，I2的增加可產生hopping效應來幫助電子傳遞，再加上蒙脫石天生負電所造成的庫倫排斥力，產生離子通道，讓電子得以順利傳遞，有效地降低R2值。
並列摘要
Our lab has recently discovered a novel method to exfoliate mortmorillonite (MMT) by using the soap-free emulsion polymerization. Because the exfoliated MMT nanoplatelets (exMMT) carry negative charges, they are capable of gelatinizing the 1-methyl-3-propylimidazolium iodide (PMII) ionic liquid, achieving a merit of no evaporation and no leaking properties. When they were employed to gelatinize the ionic liquid electrolyte for dye-sensitized solar cell (DSSC), it was surprised to find that the power conversion efficiency (PCE) was increased from 6 to 7.77%. Therefore, the main objective of this master thesis was to investigate the structure and solution conductivity of exMMT. Also, a kind of amine-terminated polymer was synthesized to exfoliate montmorillonite in order to compare the results with that synthesized by soap-free emulsion polymerization method. First, TEM and AFM were used to examine the structure of exMMT. It was shown that the size of exMMT was about 300 nm in width and 1 nm in height. Second, we used XRD to determine that exMMT would re-stack to some degree by itself after drying and calculate that the tilt angle of remaining amine-terminated polymer was ~6 degree on exMMT surface. Besides, the effect of exfoliator on the metallic ions of MMT is also in need of discussion. We used FT-IR to investigate the change of the spectrum after exfoliation of the MMT and XPS to measure the change of binding energy of the metallic ions on MMT. The FTIR results showed that the peak of Si-O became broader in both methods and that of Mg-O was diminished in anionic method. The former told us that MMT was actually exfoliated while the latter showed that the structure of MMT was changed due to the presence of anionic exfoliator. When we used XPS to investigate the change of binding energy of the metallic ions on MMT, it was shown that the peak of Mg1s orbital shifted to the lower energy in anionic method while Si, Al and Mg were all affected in cationic method. After that, the electrochemical properties of the exMMT/PMII composites prepared by two different methods of MMT exfoliation were examined and compared. The EIS result showed the impedance for the exMMT/PMII hybrid decreased with increasing the MMT weight percent, especially near gel point. We used Raman spectroscopy and XPS to clarify this unexpected result by determining that I3- and I5- were formed by the oxidation of I- in the presence of exMMT. Last but not least, by means of EIS, we found that the increase of I2 concentration could help the transfer of electrons by hopping effect when adding different amount of I2 in exMMT/PMII.