Polymer and Liquid Crystal Assembled Nanomaterials

这项研究计划的主要主题是在固体核磁共振表征的辅助下，将纳米材料组装成有组织的、对刺激有反应的结构。1.片状纳米颗粒(NPs)。本主题涉及基于聚合物的“片状纳米颗粒”的制备、表征和组装，其定义为具有至少一个定义良好的片状颗粒以允许与其他颗粒或表面进行定向相互作用的颗粒。片状粒子是光子胶体晶体、多室给药剂和催化剂的研究热点。障碍包括缺乏大规模的准备工作和适当的定性工具。对具有混合聚合物外壳的NPs的理论研究预测，相分离的日冕会提供柔软、可变形的“斑块”。我们最近开发了一种简便的配体交换方法，用混合聚合物刷制备纳米粒子，并用核磁共振表征了纳米相的分离。通过改变NP的大小和形状以及聚合物配体的比例和链长，将测试片状NPs到分级超结构中的受控组装。2.聚合物功能化液晶纳米粒子。第二个主题融合了我的团队的两个专业领域，聚合物功能化NPs和NP-液晶分散体。主要目标是开发合适的聚合物配体来取代定制合成的介晶配体，这些配体通常用于形成稳定的NP-LC分散体，将聚合物和NP添加剂的优势结合到LC中。纳米粒子的掺杂可以增强液晶的电光性质，反之，液晶可以将纳米粒子模板化为规则的空间结构。液晶-聚合物共混物被广泛应用于显示器应用，但对液晶-聚合物界面的了解还很少。对液晶-聚合物共混物的理论/实验研究，以及对与纳米粒子捆绑在一起的聚合物的研究，将考察链的构象和动力学，以了解分子水平的聚合物-液晶相互作用。由于聚合物在LCS中的相容性与链的刚性密切相关，因此将对柔性和刚性棒状聚合物进行研究。3.通过表面化学调整NP的性质。第三个主题集中在表面化学对无机NPs性质的影响。由于表面原子构成了NP的重要组成部分，因此配体的壳层组成可以决定NP的结构。卤化铅钙钛矿是一类很有前途的新型半导体纳米晶。在将这些纳米碳化物用于太阳能电池或光电子器件之前，需要进行有效的表面化学处理，以防止受潮、光或热的降解。另一种新的纳米材料-铁电BaTiO(BTO)纳米立方体将被研究，以了解为什么它保持铁电，尺寸小于理论预测，这对非易失性存储器和其他应用至关重要。核磁共振实验将允许通过配体交换反应检测表面重建，以及将配体匹配到特定的表面结合位置。

The main theme of this research program is the assembly of nanomaterials into organized, stimuli-responsive structures, assisted by solid-state NMR characterization. 1. Patchy Nanoparticles (NPs). This topic concerns the preparation, characterization and assembly of polymer-based "patchy nanoparticles", defined as particles with at least one well defined patch to allow directional interactions with other particles or surfaces. Patchy particles are of interest for photonic colloidal crystals, multi-compartmental drug delivery agents and catalysts. Obstacles include a lack of large-scale preparations and suitable characterization tools. Theoretical studies of NPs with mixed polymer shells predict phase separated coronas that provide soft, deformable "patches". We recently developed a facile ligand exchange method to produce NPs with mixed polymer brushes and characterized the nanophase separation by NMR. Controlled assembly of patchy NPs into hierarchical superstructures will be tested by varying the NP size and shape and the ratios and chain lengths of the polymer ligands. 2. Polymer Functionalized NPs in LCs. The second topic merges two areas of expertise of my group, polymer functionalized NPs and NP-liquid crystal dispersions. The main goal will be to develop suitable polymer ligands to replace custom-synthesized mesogenic ligands typically used to form stable NP-LC dispersions, combining the advantages of polymer and NP additives to LCs. NP dopants can enhance LC electro-optical properties and conversely LCs can template NPs into regular spatial structures. LC-polymer blends are widely used for display applications but the LC-polymer interface remains poorly understood. Theoretical/experimental studies of LC-polymer blends, followed by studies of the same polymers tethered to NPs, will examine the chain conformation and dynamics to understand the molecular level polymer-LC interactions. Since the miscibility of polymers in LCs is strongly correlated with the chain stiffness, both flexible and rigid rod polymers will be studied. 3. Tuning NP Properties via Surface Chemistry. A third topic focuses on the effect of the surface chemistry on the properties of inorganic NPs. Since the surface atoms make up a significant fraction of a NP, the ligand shell composition can determine the NP structure. Lead halide perovskites are a promising new class of semiconductor nanocrystals (NCs). Before these NCs can be used for solar cells or opto-electronic devices, an effective surface chemistry is needed to prevent degradation from moisture, light or heat. Another new nanomaterial, ferroelectric BaTiO3 (BTO) nanocubes, will be studied to understand why it remains ferroelectric down to sizes smaller than theoretical predictions, critical for non-volatile memory and other applications. NMR experiments will allow detection of surface reconstruction by ligand exchange reactions as well as matching of ligands to specific surface binding sites.