纳米聚苯胺成核机理的研究：结构演变与分子作用机制

Current understanding on the anisotropic growth from the aniline oligomers to polyanilines in different morphologies is limited due to the shortage of the appropriate methodology to characterize this process. The major difficulties come from the following aspects:1) the number of the nuclei is scare which makes the signal is too feeble to be detectable; 2) the signal evolves too fast due to the transient nature of this process; and 3) all interested signals are overlapped severely, leading the spectral interpretation significantly hard. Fortunately,we observed the water molecules in the solvation layer of the micelle can be served as the ideal probe molecules for the detection of the nucleation mechanism due to the following considerations:1)all molecules involved in the nucleation carries the information of this process, and therefore theoretically the detection of water molecules enables us to derive the same information as those from other species;2)these molecules are large in number and can respond to the external interruptions quickly due to their high mobility, making them the best probes for detection. While superior in nature, these molecules can exchange fastly with the water molecules in bulk leading to an average signal observed eventually which encumbers their applications in the mechanistic studies. To overcome this difficulty, we found that culturing the micelle into a bigger size can increase the thickness of the solvation layer while enhance the capability of the water molecules therein withstanding the violent shocking from the other species' structural arrangements in the nucleation.In this way,those water molecules carrying the information of nucleation have a life time long enough and enable to be served as the ideal probe moelcules for the detection. On the basis of these results, we are trying to carry out the gradient selected pseudo-two dimensional NMR experiments via selective excitating the resonances from species such as water or in situ formed oligomers in the reaction.Our main focus is on the understanding the structural evolution and the molecular interactions underneath each transition, in paticular the evolution of the dipolar couplings of the major species in the nucleation period. In summary, we are endeavored to dig out the predominant step-wised proedures for the formation of major polyaniline nanotructures (such as nanotubes, nanorod, nanosponges and so on)as well as the major intermolecular interactions that dictate the corresponding structural generation. This projection is of fundamental importance for the understanding of the formation mechanism of nanostructured materials and the nature of the self-assembly process and thus will be of great value in academic and industry.

目前对导致纳米聚苯胺各向异性生长为特定形貌最关键一步：游离寡聚物分子变为电镜可观测的聚集态过程的认识异常匮乏，这归因于此转变过程速度快，分子间作用力复杂及成核物种稀少使相关信号衰减过快，强度过弱，重叠严重而难以捕捉与解析。最近我们发现以胶粒水化层中的水分子为探针结合诸共振吸收峰随反应时间的变化规律可破解此难题，因为胶粒水化层中水分子同样感受成核变化，载有成核信息，但其绝对数目多，能及时反映成核环境变化。 目前囿于此类分子能与本体水分子发生快速交换使信号平均化而难以开展相关工作，我们通过增大胶粒尺寸以增加水化层厚度减缓以上交换过程并增强其抵抗成核冲击的能力使检测成为可能。本申请拟在此基础上进一步采纳选择性激发与脉冲梯度场技术将二维核磁降维为一维核磁定性与定量地揭示聚苯胺成核过程中聚集态结构演变与分子作用机制，重点考察偶极作用的变化规律。本工作对全面认识有机乃至无机纳米材料的成因具有重要意义。

对成核机理的认识是辨析晶体各向异性与不同纳米结构晶体形成机理的基础。在前期工作基础上，我们主要通过胶束水化层的水分子探测成核过程的信息。胶束水化层的水分子处于胶束最外层，能首先感受到外部刺激，因而始终参与核形成引起的多种结构重排。为减缓成核过程中相关信号衰减太快，实验中将胶束长时间静置，这样大尺寸的胶束具有更强的抵抗外部冲击的能力，延长了相关信号并避免其过快衰减于背景噪音之中。以聚苯胺为模型化合物，将原位核磁共振（In-situ NMR）与透射电镜（TEM）技术结合，主要研究了胶束和类胶束体系中聚苯胺（PANI）的成核机理。. 第一，胶束体系主体由苯胺和十二烷基硫酸钠（SDS）构成，通过樟脑磺酸（CSA）诱导胶束形体转变为双层结构和双连续结构胶束。主要包括：1）通过NMR研究CSA诱导球形胶束经椭球形中间状态到双层结构的转变过程。将上述双层胶束高度取向的苯胺引发聚合，获得夹有SDS双层的三明治结构聚苯胺纳米片，它具有良好的电容性能。对胶束转变过程及纳米片形成过程开展了原位1H NMR、自旋晶格弛豫时间（T1）等实验。2）研究了棒状向双连续结构的胶束转变和双连续结构胶束中纳米孔道聚苯胺的瞬时成核过程。采用一系列1H NMR及紫外可见光谱实验监测纳米孔道聚苯胺的形成，产物形貌经TEM观察具有的开孔结构。. 第二，类胶束体系由有机酸与苯胺构成，主要包括：1）以水杨酸和苯胺为主体，研究表明苯胺与水杨酸通过弱分子间作用力形成类胶束的动力学性质，聚集体成核过程显现出大多数组分具有弱的分子间偶合与高的分子运动能力。采用1H NMR、J-分辨等实验调查了球形类胶束的形成机理，基于原位1H NMR、T1、奥弗豪塞尔核效应（NOE）等演变信息，从分子尺度剖析了聚苯胺纳米管、和空心微球的成核机理。2）利用1H-NMR原位追踪在L-缬氨酸存在下合成花状纳米聚苯胺的形成过程，发现此结构的形成经历三个阶段：i）在苯胺与缬氨酸构成的类胶束结构内聚合成吩嗪类寡聚物；ii）通过π-π重叠作用及胶束融合过程成为片状聚集体；iii）通过与缬氨酸形成氢键组装成花瓣状纳米聚苯胺。