Zahra Fakhraai - US grants

Technical Summary
Molecular glasses with high densities and exceptional kinetic stabilities have been recently produced by means of physical vapor deposition (PVD). In these experiments, the substrate temperature was held at a temperature below the glass transition temperature, Tg, where the bulk relaxation dynamics are extremely slow. In order for these PVD glasses to overcome the kinetic barriers preventing bulk glasses from reaching such near-equilibrium states at low temperatures, molecules must have access to enhanced mobility during vapor deposition. It is hypothesized that this enhanced mobility is caused by a layer of increased mobility close to the air interface. With support from the Solid State and Materials Chemistry program in the Division of Materials Research, this hypothesis will be tested by studying the dynamical properties of the surface of organic molecular glasses using a nanoparticle probe technique developed by the PI and others. The proposed improvements to this technique will allow simultaneous studies of the properties of the bulk glass and its free surface, making it an ideal method for investigating the correlation between surface properties and stable glass formation. This technique will be applied on a broad range of organic molecules to investigate whether this phenomena is universal for all glasses, or a chemical effect specific to particular molecular structures. These studies will be important in advancing our fundamental understanding of the glass transition phenomena.

Non-Technical Summary:
Glasses, out of equilibrium solids with structures that resemble that of equilibrium liquids, are ubiquitous in our daily life, and are widely used in the electronic and medical industries. Despite this, developing new useful glassy materials, or improving the properties of known glassy materials has proven to be difficult due to extremely slow molecular motion within the glass. For example, in order to make high-density glasses via aging, the process by which a glass naturally becomes more dense, one would have to wait a few hundred thousand years. A recent discovery, however, shows that glasses with highly desirable properties, such as increased density and stability, can be produced in a few hours. It is hypothesized that this is caused by the presence of a layer at the air/glass surface of most organic and polymeric glasses that is a few nanometers thick and behaves like a liquid rather than an out of equilibrium solid. Our proposed studies aim at understanding the origins of the liquid-layer and its effect on the structure of glasses. Understating the properties of the liquid-layer can help design and produce materials with improved properties for organic electronic, pharmaceutical, lubrication and coating technologies. Furthermore, we will combine these studies with educational efforts aimed at introducing concepts of glassy polymer dynamics and structure to a wide audience. Polymers are widely used in everyday life. Products such as bullet proof glass, silly putty and tires are examples of materials with similar design concepts, but widely varying properties. We will design experimental modules to highlight the importance of chemical composition, structure and dynamics on the final properties of a polymeric system. These experiments will be presented with adjustable levels of technical detail so that students of all backgrounds can learn from them. The PI will also work closely with institutions at the University of Pennsylvania and science teachers from elementary and high schools in the Philadelphia area to develop, implement, and disseminate these modules. To reach an even larger audience, videos of these modules will be made available online.

Part 1:
This Partnership in Research and Education (PIRE) project addresses critical research challenges for the development of Active Coating Technologies (ACTs) through an international research and educational platform with an aim to transform the human habitat and our ability to respond to disasters. These ACTs will generate fundamental scientific understanding that enables the design of novel materials and properties for the robust collection and purification of water, elimination/reduction of disease transmission, and efficient generation and storage of energy, and hence, will address societal needs that have high relevance for the world and the U.S. To this aim, the University of Pennsylvania has formed an international partnership with fourteen collaborators from six institutions within the Grenoble Innovation for Advanced New Technologies (GIANT) in Grenoble, France. The collaboration with Giant provides the complementary expertise and resources critical for the research. The domestic partners, namely, Alabama State University, Villanova University and Bryn Mawr College further increase the research depth and diversity of participants, who will take part in every aspect of the project including research and education at GIANT. Through the planned research programs every summer, the US team consisting of a post doc, an early career faculty, and graduate and undergraduate students from these domestic institutions and UPenn, will gain invaluable international research experiences at Grenoble. Other important educational components include industrial internships at Salvoy, a world leader in the area, as well as workshops to develop broader career skills, training for the communication of technical information, and the opportunity to innovate on a prototype "Relief Tent" that will showcase ACT research. The research will address fundamental and up-to-now unsolved, materials-related scientific problems that will be applicable to engineering better human habitats and emergency response structures. The integrated research and educational components of the project will contribute to preparing a globally-engaged science and engineering workforce and a new cadre of US scientists poised to be international scientific leaders.

Part 2:
To enable coatings that transform the human habitat, each ACT utilizes the versatility afforded by polymers, nanoparticles and their mixtures to create coatings with tailored chemistry, surface texture and function. ACT 1 (water management) seeks to understand how the size, geometry, and surface energy of hierarchically structured coatings influence wetting and water transport. GIANT adds expertise in photoreactive nanomaterials that, when combined with Penn's structured coatings, open new opportunities to manage water. US scientists can investigate wetting of structured coatings using micro beam x-ray scattering tools at GIANT. ACT 2 (suppression of disease transmission) will relate the mechanics and texture of nanobilayer and layer-by-layer coatings to bacteria adhesion and proliferation. GIANT's expertise in synthesis and visualization of biomacromolecules is critical for understanding how bacteria interact with novel surfaces. ACT 3 (energy conversion and storage) will design multilayered coatings to efficiently collect and convert light using textured surfaces from ACT 1 in combination with unique nanoparticles. These photovoltaic cells will be coupled with solid polymer electrolytes designed with fast ion pathways for next generation lithium ion batteries. GIANT's expertise in interrogating energy materials in-situ and in-operando is particularly unique. Five unifying principles and methods integrate the ACTs, including commonality of materials and approaches, the unifying role of theory and simulation, a need for mechanical characterization and robustness, novel methods for structure/property studies at GIANT, and the translation of basic research into applications in collaboration with industry.

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.

This award supports the purchase of a state-of-the-art X-ray scattering instrument that will be operated as an open-access facility within the Laboratory for Research on the Structure of Matter (LRSM), host of an NSF-funded MRSEC at the University of Pennsylvania (Penn). The Xeuss 2.0 from Xenocs allows the structural characterization over length scales from 0.09 to 600 nm and thus facilitates study of hierarchical structures in a wide range of hard and soft materials. The anticipated scope of materials to be studied includes metals, ceramics, plastics, biological tissue, and novel combinations of these. The instrument will also play a vital role in the materials education and training of the many high school, undergraduate and graduate students, visiting scientists, post-doctoral associates and local high school teachers who participate in LRSM programs. The facility will also develop and administer workshops and online training materials to promote its broad use by beginners and to fully develop expert-users and thus promote knowledge exchange and technology transfer. The open-access facility will be used by scientists and engineers from local companies and colleges/universities to advance their research. Besides providing unique training in fields critical for US technological competitiveness, the discoveries and understanding facilitated by the new instrumentation will underpin future technologies, thereby informing industry, stimulating the economy, and offering benefits to society at large.

This grant enables the purchase of a state-of-the-art X-ray scattering instrument for an open-access facility within the Laboratory for Research on the Structure of Matter (LRSM), host of an NSF-funded MRSEC at the University of Pennsylvania (Penn). The Xeuss 2.0 by Xenocs enables materials characterization across an extraordinarily wide range of cutting-edge research programs at Penn and in the Philadelphia/Delaware-Valley region. The dual Cu-Mo source and adjustable sample to detector distances provide structural information at both high and low spatial resolution across a wide range of length scales (0.09 to 600 nm). An assortment of sample environments enables materials to be manipulated in situ and operando to probe their structural evolution in response to temperature, tensile stress and electric/magnetic fields, even in humid and liquid environments. Thus, the instrument will advance research on the synthesis, fabrication, processing, and assembly of a wide range of materials systems, and will provide crucial insight about structure relevant to their chemical, electrical, magnetic, mechanical, optical, thermal, and transport properties. The anticipated materials usage portfolio includes nanoporous metals for catalysis and energy storage; nanocrystals, nanorods, and nanocrystal superlattices for light harvesting; polymer nanocomposite films for thermal management, optical properties, and scratch resistance; acid- and ion-containing polymers displaying micro-phase separation for ion transport; dendrons, dendrimers, and their self-assembled structures; hierarchical polymer-based films for controlled wetting; chromonic liquid crystals with novel self-assembled structures and phase transitions; inorganic microlaminated thin films wherein fabrication methods control magnetic properties; thin film molecular glasses with controlled stability and toughness; hierarchical protein structures in squid lenses and other tissues; polycarbonates in ionic liquids to manipulate chemical reactivity; and oriented protein films for electromechanical coupling. The new instrumentation is critical for at least 17 research groups, including 12 from Penn spanning 7 academic departments, and 3 from local universities. Additionally, the instrument will advance proprietary/open-publication research of nearby industrial partners. The Xeuss 2.0 will play a vital role in the materials education and training of the many high school, undergraduate and graduate students, visiting scientists, post-doctoral associates and local high school teachers who participate in LRSM programs.

This Future Manufacturing Research Grant (FMRG) CyberManufacturing grant supports research that develops new knowledge related to on-demand, flexible manufacturing of high quality two-dimensional (2D) nanomaterials, such as MXenes. A multidisciplinary team develops the fundamental science for industrial-scale production of 2D titanium carbide MXene flakes economically and with high yield. Due to their superior mechanical and electronic properties, MXenes have applications in electronics, biomedical devices, sensors, catalysts, gas separation, water purification, conductive coatings and smart fabrics, each of which has a large market size which enhances U.S. manufacturing competitiveness, economy and national security. MXenes are currently being produced with highly varying quality at small laboratory scale. This quality inconsistency is due to the high sensitivity of MXene production to processing conditions, variability in raw material quality and poor understanding of atomic- and molecular-level processes. This research aims to understand these processes and use this understanding to enable industrial-scale nanomanufacturing of 2D nanomaterials. The project involves several disciplines including chemistry, chemical engineering, materials science and engineering and computer science. The project helps broaden the participation of women and underrepresented minorities in research and positively impacts engineering education.

This project aims to address nanomanufacturing challenges such as rapid discovery, design, and customization of 2D nanomaterials with desired end-product properties. These challenges are addressed by studying, developing, deploying and testing innovative cyber manufacturing solutions. The research involves real-time process monitoring and control and tracking of nanomaterial macroscopic and microscopic properties. The effect of Ti3AlC2 structure, defects and grain morphology on the properties of the resulting Ti3C2 MXene model system is investigated to gain knowledge needed to control extrinsic defects, such as Ti vacancies due to etching and delamination, surface termination compositions and intercalant species. The atomic- and molecular-level processes that are critical for the nano- and macro-scale properties of Ti3C2 are studied theoretically, via first principles calculations and molecular dynamics simulations, and verified experimentally to determine their effects on defects, flake morphologies, and final functional properties. To capture quantitative relationships between nanomaterial properties, manufacturing conditions and nondestructive characterizations such as Raman, SERS and STEM are utilized. Deep neural network models are developed, trained, and deployed to capture and represent these relationships in readily available forms. Technoeconomic analysis and life cycle assessment ensure the economic viability, safety and sustainability of the envisioned nanomanufacturing industrial-scale platform for MXene production.

This project is supported with co-funding from Civil, Mechanical and Manufacturing Innovation (CMMI) and Engineering Education Center (EEC) Divisions in the Engineering (ENG) Directorate, the Division of Materials Research (DMR) and Chemistry (CHE) Division in the Directorate for Mathematical and Physical Sciences (MPS), and the Division of Undergraduate Education (DUE) in the Directorate of Education and Human Resources (EHR).

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.