【作者】 唐群委；

【导师】 吴季怀；

【作者基本信息】 华侨大学 ， 材料学， 2009， 博士

【摘要】 自组装多层膜已经引起了来自不同领域科学家的广泛关注。自组装多层膜主要存在于气/液或液/固界面上,且很容易通过层-层自组装技术来构建。1991年,Decher发展了一种基于阴、阳聚电解质间静电作用为推动力的制备多层膜的方法,由此揭开了自组装多层膜制备与研究的新篇章。本论文旨在采用自组装法制备高导电性多层膜,研究多层膜的电导率与结构的关系,提出了相应的导电机理,促进高导电性自组装多层膜的发展。在论文的第二章中,采用十六烷基三甲基溴化铵(C16TAB)修饰氧化石墨(GO)与聚丙烯酸(PAA)进行静电自组装。实验表明通过C16TAB表面修饰后,GO可与PAA牢固的吸附,制备的多层膜具有较高的导电性。由于PAA分子链可以扩散进入纳米GO薄片层间,致使GO薄片层间距扩大甚至剥离,当GO层间距(或组装层数n)增大至渗滤阈值时便会产生渗滤效应。采用分子量为2000-4000的PAA组装的多层膜具有典型的PTC/NTC效应。分子量较低的PAA更容易扩散至GO层间,导致多层膜产生更高的电导率和更低的渗滤阈值。将(PAA/GO)n多层膜还原后,电导率得到极大提高,渗滤阈值向较高组装双层数移动。依此,我们获得了组装高电导率和低渗滤阈值多层膜的新方法。在论文的第三章,利用与第二章类似的静电自组装方法,成功地实现了C16TAB修饰的石墨(G)与聚苯乙烯磺酸钠(PSS)的层层自组装。实验结果表明将纳米GO薄片还原后的表面更易被C16TAB修饰,所制备的(PSS/G)n多层膜的电导率得到极大提高。当多层膜的厚度达到52纳米时,便会克服表面粗糙度与形貌的影响,产生渗滤现象,渗滤阈值n=4时,电导率最高可达204.1 S/cm。在论文的第四章,我们首先提出用聚合—生长两步法(无需任何模版)制备了高度有序的PANI阵列。实验结果证实苯胺浓度、酸用量、酸浓度及酸种类对PANI纤维阵列的形貌具有很大影响,实现了PANI阵列的尺寸与形貌可控性,通过优化制备条件可以制备出高度有序的PANI薄片和纤维阵列。研究了高度有序PANI阵列的生长机理,发现苯胺阳离子为PANI阵列的生长起到“模板”作用。采用XRD、UV-vis及FTIR测试表明,PANI阵列具有有序的分子构象和较高的结晶性。制备的PANI阵列的电导率与温度的关系符合准一维可变程跳跃模型,显示出半导体特性。在论文的第五章中,我们采用第四章中制备的高度有序PANI纤维阵列与PSS制备了(PSS/PANI)n自组装导电多层膜。实验结果证明PANI纤维阵列溶解后仍呈纳米颗粒状,保持良好的晶体结构,所制备的多层膜比采用传统法制备的PANI颗粒制备的多层膜具有更高的电导率、电化学活性和更低的渗滤阈值。在论文的第六章中,研究了采用旋涂自组装技术制备(PSS/G+/G-)n多层膜。结果表明不同PSS/G+/G-比例制备的多层膜与组装层数均呈线性关系;相同组装层数与相同旋涂转速时,不同PSS/G+/G-比制备的多层膜中PSS的组装量相等,而G(G++G-)的组装量则与G层数成正比例关系;旋涂转速ω越高,所制备的多层膜越薄,且G的组装量与ω-1/2呈正比关系。PSS/G+/G-比例高的多层膜具有较高的电导率和较低的渗滤阈值,较高的旋涂转速制备的多层膜具有较低的渗滤阈值。采用目数较大的纳米石墨片组装的(PSS/G+/G-)n旋涂自组装多层膜具有更高的电导率与更低的渗滤阈值。我们采用自组装法制备多种高导电性多层膜,研究了多层膜的制备条件—结构—导电性之间的系统关系,发现了多层膜的电导性渗滤现象,提出了其导电机理。这些结果在导电多层膜的制备方法,导电性能和导电机理等方面深化和拓展了自组装导电多层膜研究范畴,促进高导电性自组装膜的发展。更多还原

【Abstract】 In recent years, the self-assembled multilayer films have attracted much attention from the scientists in many fields. In general, self-assembled multilayer films exist in the interfaces between gas and liquid or liquid and solid. In 1991, professor Decher developed a simple route to fabricate multilayer films using the electrostatic interaction between cationic and anionic polyelectrolytes as driving force. This technique is believed to be a rapid and simple way to produce multilayer films where the film composition and thickness can be adjusted by controlling the preparation coditions. The method has been regarded as an important milstone for the multilayer film research. In this dissertation, we focus on the preparation of multilayer film with high conductivity by self-assembled method, investigate the relationship between electrical conductivity and structure of the multilayer film, and try to propose a theory to reveal the conductive mechanism, which will promote the development of the conducting self-assembly multilayer films.In chapter 2, a multilayer (PAA/GO)n consisting of poly(acrylic acid) (PAA) and graphite oxide (GO) nanoplatelets modified with cationic surfactant cetyltrimethylammonium bromide (C16TAB) is self-assembled successfully by using the electrostatic interaction. The results show that C16TAB modified GO nanoplatelets can adsorb PAA chains firmly, and the multilayer films show high conductivity. Because of the fact that PAA chains can diffuse into the interlayer of carbon molecular layers, the interlayer interaction is weakened and the interlayer height is expanded. When the C-C interlayer height reaches a threshold value (or n reaches a threshold value), the electrons in the carbon interlayer become free, and a percolation effect appears. The multilayer film has typical PTC/NTC effects if the PAA with an average molecular weight ranging from 2,000 to 4,000 is used to fabricate the multilayer films. The results also prove that the PAA chains with lower molecular weight can diffuse into the interlayer of carbon molecular layers easier, which will result in the fabrication of the multilayer films with higher conductivity and lower percolation threshold value. After reduction by hydrazine hydride, the conductivities of the conducting films are dramatically improved, and the percolation threshold occurs at high number of bilayers. By this assembling method, we develop an approach for self-assembly of the multilayer films with high conductivity and low percolation threshold value.In chapter 3, we successfully fabricate the (PSS/G)n conducting films consisting of C16TAB modifed graphite nanoplatelets and PSS polyelectrolyte. The results reveal that the reduced graphite nanoplatelets can be easily covered by C16TAB. Compared with (PAA/GO)n multilayer film, the conductivity of (PSS/G)n film is improved greatly. When the thickness of multilayer film is greater than 52 nm, a percolation effect appears, the multilayer film shows a percolation threshold at n = 4 and the highest conductivity of 204.1 S/cm.In chapter 4, we firstly propose a two-step method contained polymerization and growth process to prepare highly oriented PANI arrays without any templete. The results demonstrate that aniline concentration, acids dosage, acids concentration and species have great effects on the morphology of the PANI arrays, which realize the size and morphology controllability. We can obtain highly oriented PANI flake and fiber arrays at optimized preparation conditions. From the experimental results, we conclude anilinium cation micelles act as“template”in the formation process. Using XRD, UV-vis and FTIR, it is found that the PANI arrays have oriented molecular configuration and excellent crystallization. Furthermore, the relationship between conductivity of the PANI arrays and temperature follow the quasi one-dimensional variable range hopping model, which show that the highly oriented PANI arrays have semiconducting characters.In chapter 5, we obtain (PSS/PANI)n multilayer films from highly oriented PANI fiber array and PSS. The results show that the PANI exist in nanoparticles after PANI arrays dissolving in the solvent, the crystallization and molecular structure of the PANI arrays are still preserved. The multilayer films present higher conductivity and lower percolation threshold value than that prepared using traditional PANI particles. In chapter 6, the spin self-assembly of (PSS/G+/G-)n multilayer films are investigated, and the results show that the deposited amount against the bilayers exhibit a linear dependence at different PSS/G+/G- ratios, indicating a progressive and uniform deposition process. The multilayer films have thinner thickness at higher rotation speed (ω), and the deposition amount of surfactants (C16TAB and sodium dodecylsulfate) modified graphite nanoplatelets against theω-1/2 exhibit a direct proportion relationship. We can control the conductivity and percolation threshold value by adjusting PSS/G+/G- ratios. Generally, the films prepared at high PSS/G+/G- ratio have high conductivity and low percolation threshold. Furthermore, we also obtain the fact that smaller size of graphite nanoplatelets are expected to fabricate the spin self-assembly multilayer films with higher conductivity and lower percolation threshold value.Based on above, we prepare some kinds of highly conducting multilayer films by using self-assembly method. The relationships between the preparation conditions, structure and conductivity are investigated, and we find a percolation behaviour of conductivity for the multilayer film, and propose percolation mechanism. These results deepen and widen the research field of self-assembled conducting multilayer films in materials preparation, conductivity properties and conducting mechanism, and promote the development of the highly conducting self-assembled multilayer films.更多还原