Engineering Stable Glass Films Using Molecular Design and Surface-Mediated Equilibration

非技术描述：小分子非晶有机材料的纳米级薄膜广泛应用于从保护涂层到有机光伏和纳米压印光刻中的抗蚀剂材料。这些薄膜通常是通过物理气相沉积（PVD）在低于材料玻璃化转变温度Tg的基板上制造的。Tg表示系统在实验室或计算时间尺度上无法达到平衡的温度。由于玻璃系统处于非平衡状态，因此其制造的精确方法，包括衬底温度，其性质和沉积速率，可以深刻地影响这些应用中的材料性质和功能。本项目采用分子合成、高通量表征和分子模拟相结合的方法来设计和表征合成玻璃形成材料库，并将其作为沉积变量的函数。解决在PVD过程中形成高稳定玻璃的基本问题将对社区设计非晶有机薄膜性能的能力产生变革性影响，并为稳定玻璃在各个行业的新应用打开大门。除了影响我们对稳定玻璃形成和工业应用的基本理解外，该项目还将影响从本科到博士阶段的初级科学家的教育。本科教育融入项目的各个方面。合成玻璃形成物的起始材料是作为本科有机化学实验课程的一部分制备的。高级本科生和研究生参与玻璃形成的合成以及PVD薄膜的表征使用各种实验和计算技术。技术描述：当保持在恒定温度下时，玻璃会非常缓慢地向更稳定、密度更高的状态演变。这个过程被称为物理老化，可能需要数百万年才能达到平衡，并且只会导致性能的适度改善。最近的突破性研究表明，在低于Tg的基板上进行PVD可以获得具有数百年甚至数千年历史的玻璃的性能。据推测，这是由于在沉积过程中薄膜自由表面的流动性增强所致。通过PVD，每个沉积的分子在凝结时都经历了这种增强的迁移性，使其能够找到低能态。因此，这一过程被称为表面介导平衡（SME）。中小企业生产的玻璃具有显著的动力学稳定性，为它们在许多新应用中的应用打开了大门，但一些基本的挑战阻碍了它们的采用。最值得注意的是，对化学结构和分子间相互作用的系统理解，有机分子与底物的相互作用，以及膜厚度的影响仍然知之甚少。先前由pi开发的合成能力允许人们拨打特定的结构基序和分子间相互作用。高通量表征方法将能够快速确定材料的动力学稳定性以及稳定性与增强的表面动力学之间的关系。最后，分子水平的见解将通过粗粒度模拟的分子合成和表征实验提供。具体来说，该项目的主要目标是：1)确定化学结构对表面迁移率和SME玻璃稳定性的影响；Ii)确定膜厚对稳定性的影响；iii)确定衬底相互作用对改变材料填充物和形成稳定玻璃的能力的作用。解决这些问题将对社区设计非晶有机薄膜特性的能力产生变革性影响，并为稳定玻璃的新应用打开大门。

NON-TECHNICAL DESCRIPTION: Nanoscopic thin films of small molecule amorphous organic materials are widely used in applications that range from protective coatings to organic photovoltaics and resist materials in nanoimprint lithography. These films are frequently manufactured through use of physical vapor deposition (PVD) onto a substrate held below the materials' glass transition temperature, Tg. Tg signifies the temperature where a system is unable to equilibrate on laboratory or computational time scales. Since glassy systems are out of equilibrium, the precise method of their fabrication, including substrate temperature, its properties, and rate of deposition can profoundly affect the materials properties and function in these applications. This project employs a combination of molecular synthesis, high-throughput characterization, and molecular simulation to design and characterize a library of synthetic glass-forming materials as a function of deposition variables. Addressing fundamental questions of the formation of highly stable glasses during PVD will have a transformative effect on the community's ability to engineer the properties of amorphous organic thin films and open the door to new applications of stable glasses for various industries. In addition to the project's impact on our fundamental understanding of stable glass formation and industrial applications, this project will impact the education of junior scientists from the undergraduate level through the PhD level. Undergraduate education is integrated into all aspects of the project. The starting material for the synthesis of glass formers is prepared as part of an undergraduate organic chemistry laboratory course. Advanced undergraduates and graduate students participate in the synthesis of the glass-formers as well as the characterization of PVD films using various experimental and computational techniques.TECHNICAL DESCRIPTION: When held at a constant temperature a glass very slowly evolves towards a more stable, higher density state. This process, called physical aging, can take millions of years to reach equilibrium and only result in modest improvement in properties. Recent breakthrough studies have shown that PVD onto a substrate held just below Tg leads to a glass with properties that appear to be that of a glass that has aged hundreds or even thousands of years. It is hypothesized that this is a result of the enhanced mobility at the free surface of the film during deposition. Through PVD, each deposited molecule experiences this enhanced mobility upon condensation, allowing it to find a low energy state. As such, this process is referred to as surface mediated equilibration (SME). The remarkable kinetic stability of SME-generated glasses opens the door for their use in a number of new applications, but several fundamental challenges hinder their adoption. Most notably, a systematic understanding of the role of the chemical structure and intermolecular interactions, the interactions of the organic molecule with the substrate, and the effect of film thickness remain poorly understood. The synthesis capabilities previously developed by the PIs allows one to dial in particular structural motifs and intermolecular interactions. High-throughput characterization methods will enable rapid determination of a materials' kinetic stability as well as the relationship between stability and enhanced surface dynamics. Finally, molecular-level insights will be provided through coarse-grained simulations of the molecules synthesized and characterized experimentally. Specifically, the primary goals of this project are to i) determine the influence of chemical structure on surface mobility and SME glass stability; ii) determine the effect of film thickness on stability; and iii) determine the role of substrate interactions on altering materials' packing and ability to form a stable glass. Addressing these questions will have a transformative effect on the community's ability to engineer the properties of amorphous organic thin films and open the door to new applications of stable glasses.