【作者】 徐洁；

【导师】 薛奇；

【作者基本信息】 南京大学 ， 高分子化学与物理， 2014， 博士

【摘要】 当高分子受限在纳米尺度时,其玻璃化转变温度,结晶行为以及很多其他的物理性质与本体存在很大的差别。从分子内部结构层面探索导致该行为差异的根本原因是必要的。同时,怎样巧妙合理的利用该受限态物理行为也是我们需要思考的。首先,我们利用荧光无辐射能量转移法(NRET)研究了受限态主要影响因素之一的尺寸效应对一维受限态高分子薄膜中分子链结构影响。我们发现在平面高分子超薄膜中,尺寸受限效应迫使高分子链在薄膜体系中链间距增大。我们推测由于分子链间距离的增大减弱了分子间的耦合作用,从而导致超薄膜的玻璃化转变温度的下降。为了进一步确认这一推测,我们结合NRET和1H-NMR方法详细研究了玻璃态高分子的链间邻近度和链段运动性的关系。我们利用冷冻抽干的方法,通过改变溶液浓度制得了不同链间邻近度的粉末样品。我们发现由稀溶液冷冻抽干的样品链间邻近度大,堆积密度小。冷压实验结果表明其链段运动性显著增强。这证实了我们之前的猜想：分子链间距离的增大会减弱分子间的耦合作用,从而导致分子链运动性增强。其次,我们研究了受限态另一主要影响因素——界面效应对高分子链结构和动力学行为的影响。实验结果直接并清晰的展示了基底界面吸附作用使支撑高分子薄膜内产生一个平铺拉伸的应力,并极大的束缚了界面层高分子链的运动。然后我们通过将相同的薄膜转移到由不同的硅烷修饰的基底上,发现界面吸附越强,高分子薄膜内产生的平铺拉伸的应力越大,分子链运动越受到束缚,并发现界面吸附性质的影响深度约为40nmo。在接下来的工作中,我们希望巧妙地将受限态物质特殊的动力学性质应用到传统高分子材料冷加工研究领域。我们展示了结合纳米受限效应和剪切诱导流动方法显著加速玻璃态高分子链的流动性,从而实现冷加工的目的。NRET方法在本章节中被用来检测小球界面间的扩散程度。纳米沉降法制备的聚氯乙烯(PVC),聚碳酸酯(PC)和聚苯醚(PPO)纳米颗粒在该设计方案下均可以实现冷流。最后我们利用冷加工的方法,完全避免了PVC以往加工过程中的分解。更令人惊喜的是,我们将具有生物活性的材料作为添加剂投入到高分子加工中,并证实其生物活性在冷压成的高分子生物复合材料中完全保留。我们期待这一冷加工方法可以为传统塑料在生物应用领域中应用提供新的思路。最后我们研究了受限效应对有机半导体小分子结构的影响以及其带来的应用价值。我们利用表面增强拉曼／拉曼光谱联用的表征方法,探测了6,13-双(三异丙基硅烷基乙炔基)并五苯(TIPS-pentacene)半导体晶体膜的垂直面分子排列。我们发现溶液剪切法制备的TIPS-pentacene薄膜中处于受限界面层的分子均处于一种亚稳态的结构。我们认为这种状态的出现是由于受限效应稳定了该分子的非平衡态排列结构。由于这种亚稳态结构更有利于电荷传输,我们优化了制膜方法,降低薄膜厚度增加受限效应,最终制备出单晶亚稳态有机半导体薄膜器件,大大提高了这一有机半导体材料的性能。更多还原

【Abstract】 Confined at the nanoscale level, polymers show an anomalous behavior characterized by a shift in the glass transition temperature (Tg) and dramatic changes in crystallization and other physical properties with respect to the bulk." Size effect" and "Interfacial effect" are always suggested to be the main reasons for this variation. However, how does these two effects influence the intrinsic structure of polymers, and how these dynamic variations depend on polymer structure remain unclear. Meanwhile we also need to consider how to take advantages of the unique physical behavior of confined materials in real applications.First, we used non-radioactive energy transfer method (NRET) to characterize polymer structure in1-D confined thin film system, and correlated the changes of structure and dynamic property. We found there was a reduced interchain proximity in ultra thin polymer film. We infer that this enlarged interchain distance reduces the interchain coupling, thereby induces a decreased Tg in ultra thin polymer films.To confirm this hypothesis, we used NRET and1H-NMR to detect the interchain proximity and segmental motion of polymer glass. Freeze-dried polystyrene (PS) was found to have an increased r value and thus a reduced chain packing density, which showed an increased segmental mobility under uniaxial compression. We clarify that it is the interchain coupling that restricts the chain motion in a glassy oligomer in which chain entanglement is absent. These also confirm our assumption that the enlarged interchain distance reduces the interchain coupling, thereby induces the enhancement in segmental dynamic.Then, we explore the interfacial effect on polymer chain structure and dynamics. Our results directly and clearly show the influence on averaged interchain proximity by the present of substrate interface, suggesting the interfacial adsorption effect on polymer chain conformation. The Tg measurement indicates this interfacial adsorption greatly constrains the dynamic mobility of polymer chains in supported films. Modifying the substrate property was found to be able to change the polymer structure and dynamics for films thinner than40nm. Previous works represent the significantly changed dynamics by the present of substrate interface, while our experiment gives the direct investigation on how this depends upon polymer structure and particular interfaces.In the following work, we displayed a clear design solution to realize the low-temperature processing for general polymer systems. To realize the cold processing for general polymer systems, we investigated two approaches to accelerate the segmental mobility of polystyrene (PS) chains at temperatures far below the glass transition temperatures. One is decreasing the polymer particle size, due to the nanoconfinement effect, polymer chains in smaller nanoparticles show greater enhanced segmental mobility; the other one is applying stresses, during which the mobility of polymer chains is supposed to be strongly accelerated. Non-radioactive energy transfer method (NRET) was used to monitor the interdiffusion at the particle boundaries. Besides, polyvinyl chloride (PVC), polyphenylene oxide (PPO) and polycarbonate (PC) nanoparticles generated by nanoprecipitation method all show the room temperature processability under pressure of100MPa. Finally, we showed that the cold processing method could avoid the polymer degradation considerably and keep the biological activity of bio-additives.At last, we investigate the confinement effect on organic semiconductor molecular packing as well as its application value. We show that a combination of Raman spectroscopy and surface enhanced Raman scattering (SERS) provides a means for effective characterization of interfacial packing in6,13-bis (triisopropylsilylethynyl) pentacene (TIPS-pentacene) films. We observed that the TIPS-pentacene crystal lattices assume a non-equilibrium packing state near the substrate interface, which gradually relaxes towards the equilibrium packing near the top interface. Since this non-equilibrium packing is preferred for charge transfer, we optimize our film preparation method, and deposit a non-equilibrium packing TIPS-pentacene films with single crystalline, which shows an extremely high performance as expected.更多还原