Brush Particle-Based Building Blocks for High Refractive Index Composites

发射、吸收或弯曲光的光学器件需要机械保护，因为划痕或裂缝会导致不希望看到的光散射。这种涂层必须具有一系列不同的性能，包括机械弹性和高折射率；前者是保护底层器件所必需的，而后者确保了最大的光学性能，因为通过保护层，光会向器件弯曲。然而，大多数材料只能针对这些目标标准中的一个进行优化。在材料研究部固态和材料化学项目的支持下，Rob Macfarlane教授和他的研究小组开发了新的策略，合成由嵌入机械坚固的聚合物基质中的高折射率纳米颗粒组成的复合材料。这些材料可以很容易地在低温下形成合适的宏观形状，然后热交联成机械稳定的固体。研究人员研究了如何以及为什么用这种合成方法将高折射率成分的显著较大部分合并到矩阵中，从而产生具有理想机械和光学性能的材料。这些材料的简单合成方法可能允许在未来制造更复杂的设备，这些设备可用于定制材料反射，以诱导结构着色或抗反射特性。这些材料具有粘合剂、涂层和耦合到光学器件的传感器等优点。此外，该项目为来自弱势群体的社区大学生提供了参与STEM研究的机会，使他们能够获得当前化学研究技术的经验和对潜在职业机会的见解。该项目提供了现实世界的实践经验，以帮助这些学生追求高等教育机会或STEM职业。该项目由材料研究部固态与材料化学项目支持，使用含有大体积分数高折射率纳米颗粒的可交联聚合物接枝纳米颗粒（PGNPs）合成聚合物/纳米颗粒复合材料。系统地研究了基本的结构-性能关系，以解释这些材料的光学和机械性能是如何受到大量填料含量的影响的。由于无机含量可控（高达85 wt.%），目标材料具有可调的折射率，但也具有优于裸聚合物的优越机械性能。具体来说，研究人员研究了以下几个方面：1)开发材料通用协议来合成和交联不同无机纳米颗粒和聚合物组成的PGNPs； 2)充分表征所得到的结构的机械和光学性质；3)开发通过有序的纳米颗粒组织或不同复合成分的多层堆叠来诱导光子带隙结构的方法。基础合成科学和材料表征工作的开展使一类新的光学材料成为可能，也为将聚合物刷接枝到无机颗粒和在纳米级表面诱导形成共价键提供了更好的设计参数。这项工作既推进了固态材料的基础化学发展，又为光学器件提供了非常有用的复合材料。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical SummaryOptical devices that emit, absorb, or bend light require mechanical protection, as scratches or cracks can cause undesirable light scattering. Such coatings must have a range of different properties, including both mechanical resilience and high refractive indices; the former is necessary to protect the underlying device, while the latter ensures maximum optical performance, because through the protection layer the light gets bent towards the device. However, most materials can only be optimized for one of these target criteria. With this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, Prof. Rob Macfarlane and his research group develop new strategies to synthesize composite materials consisting of high refractive index nanoparticles embedded within a mechanically robust polymer matrix. These materials can be easily formed into appropriate macroscopic shapes at low temperatures, then thermally crosslinked into mechanically stable solids. The researchers study how and why significantly larger fractions of the high refractive index components can be incorporated in the matrix with this synthesis method, which then results in materials that have ideal mechanical and optical performance. The simple synthesis methods for these materials potentially allow for the fabrication of more complex devices in the future that can be used to tailor material reflection to either induce structural coloration or anti-reflective properties. Such materials have benefit as adhesives, coatings, and sensors coupled to optical devices. In addition, the project provides opportunities for community college students from underrepresented groups to participate in STEM research, allowing them to gain both experience in current chemistry research techniques and insights into potential career opportunities. This program enables real-world, hands-on experiences to aid these students in pursuing higher education opportunities or STEM careers. Technical SummaryWith this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, polymer/nanoparticle composites are synthesized using crosslinkable polymer-grafted nanoparticles (PGNPs) containing large volume fractions of high refractive index nanoparticles. Systematic investigations of fundamental structure-property relationships are conducted to explain how the optical and mechanical properties of these materials are affected by the large amount of filler content. The target materials possess tunable refractive indices due to the controlled amount of inorganic content (up to 85 wt.%), but also possess superior mechanical properties that surpass the bare polymer alone. Specifically, the researchers study the following aspects I) Developing materials-versatile protocols to synthesize and crosslink PGNPs with different inorganic nanoparticle and polymer compositions, II) Fully characterizing the mechanical and optical properties of the resulting structures, and III) Developing methods to induce photonic band gap architectures through ordered nanoparticle organization or multi-layer stacks of different composite compositions. The basic synthetic science and materials characterization efforts conducted enable a new class of optical materials, and also provide better design parameters for both grafting polymer brushes to inorganic particles and inducing covalent bond formation on nanoscale surfaces. This work advances both fundamental chemistry in solid state materials development and provides highly useful composites for optical devices.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.