In this project, Yu, Ediger, de Pablo, and coworkers investigated how to produce organic glasses with high stability and controlled molecular packing. Glasses are important materials that combine the mechanical strength of crystals and the spatial uniformity of liquids, making them ideal for applications ranging from telecommunication to cell-phone display to biomedical materials. Glasses, however, have two limitations. First, glasses are unstable, tending to age over time toward a denser state and also to crystallize. A second limitation of glasses is that they are usually isotropic, containing molecules in random packing, while anisotropic packing is important for such applications as organic light-emitting diodes (OLEDs).

The team has made significant discoveries in engineering the structure and properties of organic glasses:

(1) Physical vapor deposition (PVD) can produce glasses of high density, high stability, and tunable molecular packing. Ordinary glasses are prepared by cooling liquids. By PVD, the team produced glasses of such high density and stability that ordinary glasses would have to be aged for millions of years to reach the same level. Furthermore, PVD glasses are prepared to have large anisotropy, in which molecules are controlled to lie down, stand up, and form layers relative to the deposition substrate. This ability has in essence created materials that are hybrid between traditional glasses and crystals. This new ability is achieved through a cycle of computation, prediction, experimentation, characterization, and verification. Without such a cycle, it would be impossible to design materials with the precision accomplished by our DMREF team. Given that PVD glasses are widely used in OLED displays in cell phones, the unique materials developed here can potentially improve the durability and efficiency of these devices – a benefit of global scale given the number of these devices.

(2) How can PVD produce such extraordinary glasses with high density and structural order? The secret lies in the solid/vapor interface during deposition. When molecules are freshly deposited, they are in an environment of high mobility, able to make quick adjustments relative to their neighbors into a tightly packed structure. With subsequent deposition, this dense structure is buried and preserved. In addition, the interface is an anisotropic environment for freshly deposited molecules, and that anisotropy can be transferred to the product to an extent determined by interfacial mobility and deposition rate. Again, this discovery was possible only through tightly coupled computation and experimentation. Too many factors are at play: deposition rate, substrate temperature, molecular characteristics, to name a few. Adopting a DMREF approach, the team used theory and computation to guide the design of experiments, to identify important molecular characteristics, and to generate vast amounts of data which were subsequently mined to optimize key molecular and process descriptors. In this way, the team identified crucial design principles for preparing carefully engineered PVD glasses. 

(3) Polymers additives stabilize organic glasses against crystallization. The team discovered that crystals grow quickly in organic glasses because their ease of fracture and the high mobility of fracture surfaces. Polymer additives, even at low concentrations, can increase fracture toughness and suppress surface diffusion, thereby inhibiting crystallization. This approach can make more organic glasses to serve as durable amorphous materials.

The team has disseminated its findings in 20 papers in high-impact journals and through a central website: https://datahub.rcc.uchicago.edu/depablo/DMREF. The team also developed a framework for collecting, curating, and disseminating data, which may serve as a model for the general materials research community to evaluate and adopt.

Broader Impacts. 1) Building on the understanding of crystallization in organic glasses, work has begun with support from the Bill and Melinda Gates Foundation to develop low-cost amorphous drugs for global health. 2) This project has provided training for 9 graduate, 2 postdoctoral, and 2 undergraduate students. This research was incorporated into a continuing-education course offered each spring through UW-Madison’s Extension Service to a total of 100 industrial scientists. 3) The work on anisotropic glasses has stimulated intense public interest on reddit.com; a U. Chicago press release (https://news.uchicago.edu/article/2015/08/13/molecular-scientists-unexpectedly-produce-new-type-glass) has been downloaded over 200,000 times.  4) The PIs and their students were involved in UW-Madison’s PEOPLE program, designed to increase the enrollment of minority and low-income students in colleges. Between 2013 and 2016, our groups taught a three-week course each summer for a total of ~60 high school students. The PEOPLE program model has now been extended to incorporate the Collegiate Scholars Program, a six-week intensive workshop offered to talented high school students (60 each summer) from at-risk backgrounds around Chicago. Students who completed the program have nearly all entered universities. 5) In partnership with Chicago’s Museum of Science and Industry (MSI), a program was established for the MSI staff to train graduate students in 8, 4-hour workshops over 2 years to deliver scienti?c content to general audiences. The students will then present lectures on current research (including their own) to museum patrons.

Last Modified: 03/08/2017
Modified by: Lian Yu