【作者】 王会才；

【导师】 杨慕杰； 李扬；

【作者基本信息】 浙江大学 ， 高分子化学与物理， 2007， 博士

【摘要】 本论文共设计制备以下五个系列共12种新型复合高分子气敏材料:盐酸羟胺盐修饰多壁纳米碳管（CNTs）/聚甲基丙烯酸甲酯（PMMA）;Pd⁰/CNTs;聚合物接枝多壁纳米碳管及纳米碳黑;不同末端基团超支化聚合物/CNTs;聚苯胺及其复合物。采用FT-IR、NMR、GPC、TGA、TEM、SEM、UV-Vis、XRD、AFM和拉曼光谱等手段表征了其组成和结构。通过浸涂、自组装原位生长以及静电纺丝方法制备了气敏元件。研究了其对甲醇、氨气等有机和无机气体的响应特性,讨论了复合物组成及结构、气敏薄膜微观结构以及元件制备工艺等对气敏元件响应特性的影响,探讨了复合物气敏机理。研究了混酸处理CNTs气敏元件对氨气、甲醇以及三乙胺蒸汽的响应特性,讨论了其基于p型半导体的气敏机理。在此基础上,采用盐酸羟胺盐对其进行修饰,并与PMMA复合,以浸涂法制备气敏元件。研究了其对醇类和氨气的响应特性,发现修饰后纳米碳管表现出n型半导体特性,其与PMMA复合物对甲醇有快速可逆的选择性响应,响应和回复时间分别约为9s和2s。提出了纳米碳管经修饰后,发生了从p型到n型半导体的转变,讨论了其基于n型半导体的气敏机理。通过溶液共混,乙醇或硼氢化钠还原的方法,制备了聚乙烯基吡咯烷酮（PVDP）/Pd⁰/CNTs、Pd⁰/CNTs和壳聚糖/Pd⁰/CNTs复合气敏材料,以浸涂法制备了气敏元件。发现PVDP/CNTs复合物,在室温下对甲醇和乙醇蒸汽的响应灵敏度接近。而对甲醇蒸汽的响应灵敏度(S_甲醇)是单独CNTs的2～5倍,PVDP/Pd⁰/CNTs复合物的S_甲醇是单独CNTs的4～10倍,而且其S_甲醇/S_乙醇可达3～4倍,显示出对甲醇蒸汽具有一定的选择性。此外,PVDP/Pd⁰/CNTs复合物的响应稳定性和重复性也较好。Pd⁰/CNTs及壳聚糖/Pd⁰/CNTs均可在室温下检测甲烷,其对2%（v/v）的甲烷气体的响应灵敏度分别约为5%和7.3%。采用氮氧自由基调控的自由基活性聚合法,制备了苯乙烯和4-乙烯基吡啶均聚物及共聚物接枝的纳米碳管和纳米碳黑气敏复合材料,通过浸涂法制备了气敏元件。研究了复合物对低浓度甲醇、四氢呋喃以及氯仿蒸汽的响应特性,发现复合物对气体的响应与聚合物的组成结构、气敏膜微观形态以及气体性质有关,纳米碳管复合物的响应灵敏度高于纳米碳黑复合物。讨论了复合物基于直接接触及隧道效应的导电机理,并提出了对于纳米碳管复合物的气敏机理为吸附气体后聚合物的溶解膨胀,造成导电通道的破坏,以及纳米碳管与气体之间的电荷转移的协同作用。而纳米碳黑复合物的气敏机理仅为吸附气体后聚合物的溶解膨胀,造成导电通道的破坏,而且碳黑复合物对低浓度和高浓度有机蒸汽的气敏机理不同。采用熔融缩聚的方法制备了具有三种不同末端基团（-OH（HBPE）、-COOH（AHPB）、-NH₂（HBPA））的超支化聚合物,并与CNTs复合制备了气敏材料,通过浸涂法制备了气敏元件。研究了复合物对甲醇、三乙胺以及乙酸蒸汽的响应特性。复合物对气体的响应与超支化聚合物的末端基团密切相关,能与末端基团发生反应的有机蒸汽具有很高的响应灵敏度,较低的检测限,但其响应回复性较差。提出了超支化聚合物末端基团与特定气体发生化学反应,诱发电荷转移的气敏机理。通过溶液原位生长、有机酸聚合掺杂以及共混掺杂等方法制备了聚苯胺及其与纳米碳管复合物,通过在自组装修饰电极上原位生长、浸涂以及静电纺丝法制备了气敏元件,研究了其对三乙胺气体的响应特性。发现原位生长聚苯胺对三乙胺蒸汽具有响应快速,灵敏度高,回复性和重复性好,检测限低（可达ppb级）等优点,提出其响应机理为吸附气体与聚苯胺发生酸碱掺杂反应及其与掺杂酸作用的竞争反应机理。与CNTs复合后其响应灵敏度提高了一倍,这可能因为聚苯胺和纳米碳管之间形成大π电子离域,使电荷转移更加容易。樟脑磺酸共混掺杂的可溶聚苯胺的气敏特性优于对甲苯磺酸聚合掺杂的聚苯胺,而响应灵敏度由掺杂水平决定。静电纺丝制备的聚苯胺纤维型敏感元件,由于纤维比表面积较大,利于气体的吸附扩散,其响应特性明显优于薄膜型元件。更多还原

【Abstract】 Gas sensitive materials of five series of polymer nanocomposites, namely, composites of multi-walled carbon nanotubes (CNTs) chemically modified with hydroxylamine hydrochloride salt and poly(methyl methacrylate) (PMMA), composites of palladium (Pd~0) nanocomposites and CNTs, composites of polymer-grafted CNTs and nano-sized carbon black (CB), composites of CNTs and hyperbrenched polymers (HBP) with three kinds end groups, polyaniline (PANI) and its composites with CNTs, were designed and perpared, and characterized by FT-IR, NMR, GPC, TGA, TEM, SEM, UV-Vis, XRD, AFM and raman spectroscopy. Resistive type gas sensors based on the composites were prepared by the method of dip-coating, in-situ polymerization and electrospinning, etc. Their gas sensing properties towards the vapors of methanol, triethylamine, ammonia, etc. have been investigated at room temperature. The effects of the strutcure, composition and morphology of the composites and the methods of sensor preparation on their gas responses were disscused, and the sensing mechanism was explored.Gas sensing properties of the acid-treated CNTs were investigated towards the vapors of ammonia, methanol and triethylamine, and the sensing mechanism of the p-type semi-conductor was disscused. The CNTs were modified with hydroxylamine hydrochloride salt and formed composites with PMMA. Gas sensors based on the composites were prepared by the method of dip-coating. They exhibited a decreased resistivity unpon exposure to the vapors of reducing ammonia and methanol, indicating responses of an n-type semi-conductor. In addition, the response towards methanol vapor is fast, reversible and reproducible at room temperatue with response and recovery time of 9s and 2s, respectively.The composites of polyvinylpyrrolidone (PVPD)/Pd~0/CNTs, Pd~0/CNTs and chitosan/Pd~0/CNTs were developed by reducing the mixture of palladium salt, polymer and CNTs. Gas sensors based on the composites were prepared by dip-coating. It was found that PVPD/Pd~0/CNTs composite exhibited the sensitivity 1~4 times higher than that of CNTs alone towards methanol vapor at room temperature, while its sensitivity to methanol and ethanol vapors of the same concentration was almost equal. The PVPD/Pd~0/CNTs composites showed the sensitivity 1～2 times higher than that of PVPD/CNTs in the detection of methanol vapor. In addition, its sensitivity to methanol vapor is 2-3 times higher than that to ethanol vapor, suggesting a selective response to methanol vapor. The responses also showed good linearity, repeatability and stability. The composites of Pd~0/CNTs and chitosan/Pd~0/CNTs exhibited a sensitivity of 5% and 7.3%, respectively, towards 2% methane at room temperature, and the responses were recoverable, stable and reproducible. A sensing mechanism taking into account of the catalytic effect of palladium was proposed.Composites of CNTs and CB grafted with polystyrene, poly(4-vinylpyridine), poly(styrene-b-4-vinylpyridine) and poly(styrene-co-4-vinylpyridine) were prepared by a nitroxide mediated "living" free radical polymerization, and used for preparation of gas sensors by dip-coating. The electrical responses of the composites towards low concentration organic vapors of methanol, tetrahydrofuran and chloroform were investigated at room temperature. It was found that the gas sensitive properties of the composites towards the organic vapors depended on the structure, composition, morphology of the composites and the nature of the vapors. The sensitivity of CNTs composites was higher than that of CB composites. The CNTs composites exhibited a sensing mechanism different from that of CB composites. In addition, the CB composite showed different mechanism towards vapors of high and low concentration.Hyperbranched polymers with different end groups were prepared by melt polycondensation, and formed composites with CNTs to prepare gas sensors by dip coating. The response of the composites towards organic vapors of methanol, triethylamine and acetic acid were investigated. It was found that the sensitivity of the composites was closely related to the end groups of the hyperbranched polymers. The chemical reactions between the end groups of the polymers and the vapors resulted in a high sensitivity and low detection limit of their composites with CNTs. A sensing mechanism was put forward based on the interactions of the vapors with the end groups of the hyperbranched polymers.PANI and its composites with CNTs were prepared by in-situ polymerization and deposited on electrodes modified by self-assembled polyelectrolytes to prepare gas sensors. Their electrical responses to triethylamine vapor were investigated. It was found that the responses of in-situ polymerized PANI were fast, highly sensitive, reversible and reproducible, with the detection limit of ppb level. A sensing mechanism of competition between the reactions of organic vapor with PANI and the doping acid were proposed. The PANI/CNTs composite exhibited a sensitivity twice higher than that of PANI alone, which might relate toπ-electron delocalization between PANI and CNTs. Soluble PANI was prepared by polymerization of aniline in the presence of p-toluene sulfonic acid and doping polyaniline base with D-camphor-10-sulfonic acid (CSA). Their sensitivity to triethylamine vapor was related to the doping levels of PANI. Nanofibers of the CSA doped soluble PANI were prepared by electrospinning. It was found that the fibers exhibited better sensing properties than that PANI films in the detection of triethylamine vapor, which was might be due to their higher surface area.更多还原