CAREER: Solid-state molecular motion, reversible covalent-bond formation, and self-assembly for controlling thermal expansion behavior

非技术摘要实际环境中使用的材料经常暴露在温度变化中。对于户外应用中使用的材料，如混凝土，这通常是由于天气或季节变化造成的。对于计算机或电子设备等设备中使用的材料，这是由于产生热量的过剩能量造成的。热膨胀是材料对任何温度变化的反应。材料对温度的反应方式会影响其功能。如果不了解和控制材料的热膨胀行为，很可能会由于温度波动而发生失效或断裂。分子的化学结构和将固体材料结合在一起的键通常决定着热膨胀行为。混凝土等材料的行为是众所周知的；然而，有机(碳)基材料的类似行为更难预测和设计，因为这些材料通过较弱的力保持在一起。有机材料正越来越广泛地应用于电子等各个领域。平衡高材料性能和理想的热膨胀对此类应用至关重要。这个职业项目由材料研究部的固态和材料化学计划支持，开发了控制有机材料热膨胀行为的基本策略。具体地说，热膨胀是通过使用动态基团来影响的，动态基团通过经历运动或通过建立和断开将材料结合在一起的键来对温度变化做出反应。预计该项目中制定的战略将影响具有可预测热膨胀性能的新型材料的设计和制备，这些材料用于促进国家繁荣的技术应用。与研究计划相结合的是一项全面的教育、指导和外展计划，涉及从中学到研究生院每个教育阶段的代表性不足的群体。这些活动包括(1)在Tech Savvy为中学女生举办的STEM工作坊--关于“我们身边的热膨胀”的年度演示文稿的开发和实施；(2)为德克萨斯州西部的高中生举办的关于分子结构和固态特性的流动实验室实验，以及(3)为高水平的本科生和研究生举办的STEM职业准备讲习班。技术摘要这个职业项目得到材料研究部固体与材料化学计划的支持，旨在通过合成具有可控制和可预测的热膨胀行为的新型、动态固态材料来加深对有机晶体固体中热膨胀(TE)行为的基本了解。TE是一种材料对温度变化的反应。分子的化学结构和将固体结合在一起的相互作用通常决定了TE的行为。然而，其他机制，如结构灵活性或运动，可能会产生意想不到的或独特的TE。对于无机或共价网络固体，分子间作用力很强，结构组装在三维上得到很好的控制，而且TE通常是可预测的。另一方面，纯有机分子固体通过较弱的非共价相互作用在三维空间中结合在一起。将单个有机分子的自组装引导到一个固体结构中，并完全控制包括所有结晶学维度的非共价相互作用，是一项具有挑战性的工作。在有机分子固体中，非共价力、运动和柔性都会影响TE。可靠地指导、实现和控制固态运动、自组装以及预测它们对TE的影响仍然具有挑战性。这个职业项目开发了控制和调节有机分子固体中TE的基本知识和系统策略，通过(1)安装能够进行固态分子运动并可靠地开启和关闭运动的官能团，(2)使用可逆的固态共价键形成反应在单个固体内在大的和接近于零的TE行为之间切换，以及(3)利用正交的非共价相互作用控制有机分子在所有三个晶体维度的自组装。这项工作有望推进固态运动、反应性、自组装和TE的基础知识，并改变表现出动态特性的功能固态材料的设计。教育和外联活动强调以STEM为动力的教育和职业准备方法，让学生在从中学到研究生院的每个教育阶段都参与STEM活动。这是通过以下方式实现的：(1)在Tech Savvy为中学女生举办的STEM研讨会上，开发和实施了关于“我们周围的热扩张”的年度演示文稿，(2)为德克萨斯州西部的高中生举办了关于分子结构和固态特性的流动实验室实验，以及(3)为高水平的本科生和研究生举办了STEM职业准备研讨会。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical SummaryMaterials used in real-world settings are frequently exposed to changes in temperature. For materials used in outdoor applications such as concrete, this is typically due to weather or seasonal changes. For materials used in devices such as computers or electronics, this is due to excess energy that results in heat. Thermal expansion is the response of a material to any change in temperature. The way a material responds to temperature impacts its ability to function. If the thermal expansion behavior of a material is not understood and controlled, failure or fracture is likely to occur as a result of temperature fluctuations. The chemical structures of the molecules and the bonds that hold a solid material together typically dictate the thermal expansion behaviors. The behaviors of materials like concrete are well-understood; however, analogous behaviors for organic (carbon)-based materials are more challenging to predict and design because these materials are held together by weaker forces. Organic materials are becoming more widely used in a variety of fields such as electronics. Balancing high material performance with ideal thermal expansion is critical to such applications. This CAREER project, supported by the Solid State and Materials Chemistry Program in the Division of Materials Research, develops fundamental strategies for controlling the thermal expansion behaviors of organic materials. Specifically, thermal expansion is influenced through the use of dynamic groups, which respond to temperature changes by undergoing motion or by making and breaking the bonds that hold the material together. The strategies developed in this project are expected to influence the design and preparation of novel materials with predictable thermal expansion properties for use in technological applications that advance national prosperity. Integrated with the research plan is a holistic education, mentorship, and outreach program involving underrepresented groups at each education stage from middle school through graduate school. The activities include (1) development and implementation of an annual presentation on 'Thermal Expansion Around Us' at Tech Savvy – a STEM workshop for middle school girls, (2) a traveling lab experiment on molecular structures and solid-state properties for high school students in West Texas, and (3) a STEM career preparation workshop for upper-level undergraduate and graduate students.Technical SummaryThis CAREER project, supported by the Solid State and Materials Chemistry Program in the Division of Materials Research, develops a fundamental understanding of thermal expansion (TE) behaviors in organic crystalline solids through synthesis of novel, dynamic solid-state materials with controllable and predictable TE behaviors. TE is the response of a material to a change in temperature. The chemical structures of the molecules and the interactions that hold the solid together typically dictate TE behavior. However, other mechanisms such as structural flexibility or motion can give rise to unexpected or unique TE. For inorganic or covalent network solids, intermolecular forces are strong, structural assembly is well-controlled in three dimensions, and TE is often predictable. On the other hand, purely organic molecular solids are held together in three dimensions by weaker, noncovalent interactions. Directing self-assembly of individual organic molecules into a solid structure with full control over the noncovalent interactions comprising all crystallographic dimensions is challenging. Noncovalent forces, motion, and flexibility all affect TE in organic molecular solids. Reliably directing, achieving, and controlling solid-state motion, self-assembly, and predicting their influence on TE remains challenging. This CAREER project develops fundamental knowledge and systematic strategies for controlling and tuning TE in organic molecular solids through (1) installation of functional groups capable of undergoing solid-state molecular motion and reliably turning motion on and off, (2) use of reversible solid-state covalent-bond-forming reactions to switch between large and near zero TE behaviors within a single solid, and (3) control over self-assembly of organic molecules in all three crystallographic dimensions using orthogonal noncovalent interactions. The work is expected to advance fundamental knowledge of solid-state motion, reactivity, self-assembly, and TE, and transform the design of functional solid-state materials that exhibit dynamic properties. The educational and outreach activities emphasize a STEM-powered approach to education and career preparation by engaging students in STEM activities at each stage of education from middle school through graduate school. This is achieved through (1) development and implementation of an annual presentation on 'Thermal Expansion Around Us' at Tech Savvy – a STEM workshop for middle school girls, (2) a traveling lab experiment on molecular structures and solid-state properties for high school students in West Texas, and (3) a STEM career preparation workshop for upper-level undergraduate and graduate students.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.