New Routes for the Synthesis of Conductive Polymers- Graphene/Graphene Oxide Nano-Composites with Enhanced Electro-conductive Properties

Abstract

Conductive polymers have been extensively studied for their easy processing and outstanding electrical properties. Among these polymers, polyaniline (PANI) and polypyrrole (PPy) have been considered as the most promising conductive polymers because of their low cost, ease in synthesis and relatively high conductivities. There are various factors that can influence the electroconductive and thermal properties of the resulting polymers and their nanocomposites such as type of dopant/filler; morphology; polymerization method and chain structure of polymers. Different polymerization methods have been reported in the literature for the synthesis of PANI, PPy and their nanocomposites like electrochemical, chemical and oxidative polymerization. In all these processes a very strong acid (percholoric acid or hydrochloric acid) is used during the polymerization. These harsh conditions during the polymerization process results in the lowering of the crystallinity and electrical conductivities of the resulting polymers, suggesting that a polymer with high electrical conductivity obtained by polymerization must be synthesized under mild conditions. In the present study modified in-situ emulsion polymerization techniques are demonstrated to synthesize PANI, PPy and their nanocomposites with GN and GO with enhanced electroconductive properties. Characterizations revealed the formation of nanocomposites with superior morphology, crystallinity, thermal and electrical properties. Chapter 1 of this dissertation highlights the importance of conductive polymers and various polymerization techniques reported in the previous literature of synthesis different conductive polymer based nanocomposites with different carbon fillers i.e. carbon nanotubes (CNT), graphene (GN) and graphene oxide (GO), and the attempt that have been made to improve the electroconductive performance of these materials. Meanwhile chapter 2 introduces a systematic approach to disperse GO during emulsion polymerization of PANI to form nanocomposites with improved electrical conductivities. PANI/GO samples were fabricated by loading different weight percent (wt. %) of GO through modified in-situ emulsion polymerization of the aniline monomer. The polymerization process was carried out in the presence of a functionalized protonic acid, dodecyl benzene sulfonic acid (DBSA), which acts both as an emulsifier and protonating agent. The microstructures of the PANI/GO nanocomposites were studied by scanning electron microscopy and transmission electron microscopy; X-Ray diffraction; UV-Vis spectrometry; Fourier transform infrared, differential thermal and Thermogravimetric analyses. The formed nanocomposites exhibited superior morphology and thermal stability. Meanwhile, the electrical conductivities of the nanocomposite pellets pressed at different applied pressures were determined using the four probe analyzer. It was observed that the addition of GO was essential component to improve the thermal stability and electrical conductivities of the PANI/GO nanocomposites. The electrical conductivities of the nanocomposites were considerably enhanced as compared to those of the individual PANI samples pressed at the same pressures. An enhanced conductivity of 474 S/m was observed at 5 wt. % GO loading and applied pressure of 6 tons. Therefore, PANI/GO nanocomposites with desirable properties for various semiconductor applications can be obtained by in-situ addition of GO during polymerization process. Chapter 3 demonstrates a modified in situ emulsion polymerization (EP) approach convenient for the formation of polypyrrole/graphene (PPy/GN) nanocomposites with harnessed conductivities. A series of PPy/GN nanocomposites were prepared by loading different weight percent (wt. %) of GN during in situ EP of pyrrole monomer. The polymerization was carried out in the presence of dodecyl benzene sulfonic acid, which acts as an emulsifier and protonating agent. The microstructures of the nanocomposites were studied by scanning electron microscopy, transmission electron microscopy, X-Ray diffraction, Fourier transform infrared, X-ray photoelectron spectroscopy, UV-Vis spectroscopy, Raman spectroscopy, photoluminescence spectroscopy and thermogravimetric analyses. The electrical conductivities of the nanocomposite pellets pressed at different applied pressures were determined using four probe analyzer. The electrical conductivities of the nanocomposites were considerably enhanced as compared to those of the individual PPy samples pressed at the same pressures. An enhanced conductivity of 717.06 S/m was observed in the sample with 5 wt. % GN loading and applied pressure of 8 tons. The results of the present study signify that the addition of GN in the PPy polymer harnesses both electrical and thermal properties of the polymer. Thus, PPy/GN nanocomposites with superior properties for various semiconductor applications can be obtained through direct loading of GN during the polymerization process. Chapter 4 introduces a modified approach to synthesize PANI and PPy doped with GO or GN through an in situ emulsion polymerization technique. DBSA was used as both a surfactant and a doping agent during the polymerization reaction. The morphology and microstructure of the synthesized polymers and their nanocomposites were studied by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis. All of these characterization techniques confirmed the superior morphology and thermal properties of the nanocomposites. The electroconductive properties of the synthesized polymers and their nanocomposite pellets containing 5 wt. % of either GN or GO and pressed at pressures of 2, 4, and 6 tons were investigated with a four-probe analyzer. Nanocomposites showed very high electrical conductivity compared to individual PANI and PPy samples pressed at the same pressures. The addition of GO and GN not only improved the thermal stability but also significantly enhanced the electrical conductivity of the nanocomposites. This study signifies the importance of the direct loading of GO and GN during the emulsion polymerization process using DBSA as a surfactant in order to achieve the superior properties of the resultant nanocomposites. Such nanocomposites can be used for various semi-conductive applications. Furthermore in chapter 5 general conclusion and future work are discussed. |전도성 고분자는 그 자체의 간단한 공정과 뛰어난 전기적 특성으로 인하여 폭넓게 연구되고 있다. 이러한 고분자들 중에서, 폴리아닐린 (PANI) 과 폴리피롤 (PPy) 은 저렴한 비용, 합성의 용이함, 그리고 상대적으로 높은 전기전도도로 인하여 가장 유망한 전도성 고분자로 여겨지고 있다. 이러한 고분자들과 그들의 나노복합재료의 전기전도적 그리고 열적 특성에 영향을 미치는 다양한 요소들로는 도펀트/필러의 종류, 형상, 중합방법과 고분자의 사슬 구조 등이 있다. PANI, PPy와 그들의 나노복합체를 합성하기 위한 방법으로 전기화학적, 화학적, 그리고 산화 중합과 같은 다양한 중합법들이 보고되고 있다. 이 모든 공정에서는 중합과정 동안에 매우 강한 산 (과염소산 또는 염산) 이 사용된다. 이와 같은 중합 공정의 다소 치명적인 조건들은 합성된 고분자의 결정성과 전기전도도의 저하를 초래하며, 높은 전기전도도를 가지는 고분자는 안정적인 중합 조건에서 합성해야만 얻을 수 있다는 것을 시사한다. 본 연구는 GN 및 GO를 첨가하여 전기전도 특성을 강화한 PANI, PPy, 그리고 그들의 나노복합재료를 합성하기 위한 개선된 in-situ 에멀젼 중합 기술에 대하여 설명하였다. 특성 평가는 우수한 형상, 결정화도, 열적 및 전기적 특성을 나타내는 나노복합체가 형성되었음을 나타낸다. 이 연구는 뛰어난 특성의 나노복합체를 얻기 위하여 계면활성제 DBSA를 사용한 에멀젼 중합 공정 중에 GO와 GN을 직접 적가한 것의 중요성을 보여준다. 이러한 나노복합재료는 수많은 반도체 응용분야에 사용될 수 있다.; Fourier transform infrared, differential thermal and Thermogravimetric analyses. The formed nanocomposites exhibited superior morphology and thermal stability. Meanwhile, the electrical conductivities of the nanocomposite pellets pressed at different applied pressures were determined using the four probe analyzer. It was observed that the addition of GO was essential component to improve the thermal stability and electrical conductivities of the PANI/GO nanocomposites. The electrical conductivities of the nanocomposites were considerably enhanced as compared to those of the individual PANI samples pressed at the same pressures. An enhanced conductivity of 474 S/m was observed at 5 wt. % GO loading and applied pressure of 6 tons. Therefore, PANI/GO nanocomposites with desirable properties for various semiconductor applications can be obtained by in-situ addition of GO during polymerization process. Chapter 3 demonstrates a modified in situ emulsion polymerization (EP) approach convenient for the formation of polypyrrole/graphene (PPy/GN) nanocomposites with harnessed conductivities. A series of PPy/GN nanocomposites were prepared by loading different weight percent (wt. %) of GN during in situ EP of pyrrole monomer. The polymerization was carried out in the presence of dodecyl benzene sulfonic acid, which acts as an emulsifier and protonating agent. The microstructures of the nanocomposites were studied by scanning electron microscopy, transmission electron microscopy, X-Ray diffraction, Fourier transform infrared, X-ray photoelectron spectroscopy, UV-Vis spectroscopy, Raman spectroscopy, photoluminescence spectroscopy and thermogravimetric analyses. The electrical conductivities of the nanocomposite pellets pressed at different applied pressures were determined using four probe analyzer. The electrical conductivities of the nanocomposites were considerably enhanced as compared to those of the individual PPy samples pressed at the same pressures. An enhanced conductivity of 717.06 S/m was observed in the sample with 5 wt. % GN loading and applied pressure of 8 tons. The results of the present study signify that the addition of GN in the PPy polymer harnesses both electrical and thermal properties of the polymer. Thus, PPy/GN nanocomposites with superior properties for various semiconductor applications can be obtained through direct loading of GN during the polymerization process. Chapter 4 introduces a modified approach to synthesize PANI and PPy doped with GO or GN through an in situ emulsion polymerization technique. DBSA was used as both a surfactant and a doping agent during the polymerization reaction. The morphology and microstructure of the synthesized polymers and their nanocomposites were studied by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis. All of these characterization techniques confirmed the superior morphology and thermal properties of the nanocomposites. The electroconductive properties of the synthesized polymers and their nanocomposite pellets containing 5 wt. % of either GN or GO and pressed at pressures of 2, 4, and 6 tons were investigated with a four-probe analyzer. Nanocomposites showed very high electrical conductivity compared to individual PANI and PPy samples pressed at the same pressures. The addition of GO and GN not only improved the thermal stability but also significantly enhanced the electrical conductivity of the nanocomposites. This study signifies the importance of the direct loading of GO and GN during the emulsion polymerization process using DBSA as a surfactant in order to achieve the superior properties of the resultant nanocomposites. Such nanocomposites can be used for various semi-conductive applications. Furthermore in chapter 5 general conclusion and future work are discussed.