My Research
As a researcher in materials science and polymer engineering, I have contributed to groundbreaking innovations with societal impacts, particularly in the field of organic electronic materials. As I shift my attention towards ceramic materials, I look forward to developing new methods of additive manufacturing via reaction bonding of dense and high temperature materials for space exploration. Below is a list of my research endeavors and their impact.
In my current project, which is a collaboration between the Faber Group at Caltech and NASA's Jet Propulsion Laboratory (JPL), I am studying a new method of additive manufacturing (AM) for high temperature materials. To achieve more intricate studies of the surface of Venus, materials must be optimized which are non-magnetic and can survive elevated temperatures and corrosive environments. Using materials designed at JPL's Additive Manufacturing Center, I will acquire an understanding of the reaction-bonding process as coupled with AM. I will achieve this goal by characterizing the reaction kinetics and microstructural evolution of the entire process, while also interpreting the chemistry of reaction-bonded constituents and elucidating the mechanical response as a function of processing conditions and AM structures. By exploiting the use of molten phases to produce composite materials
for conventional two-phase microstructures or materials with a continuous interfacial phase created from the molten,
reaction-bonding phase, this work will provide a blueprint for better thermo-mechanical integration of ceramics with space craft componentry. Additionally, these studies will provide the foundation for broader ceramic composite exploration and development, while bringing a new material class - ceramic systems - to meet NASA's strategic goals.
Flexible Partially Conjugated Polymers as the Ductile Matrix in Blend Systems.
For this project, I have blended a conjugated polymer (PNDI-C4), which exhibits high ductility, with a fully conjugated polymer (PNDI-C0) in the hopes of combining both high ductility and electrical performance. Upon blending, we observed the phase separation of the polymers to form a given morphology. Through the duration of this project, we employed wide-angle x-ray scattering (WAXS) analysis to monitor the crystalline alignment, polarized ultraviolet (UV)-Visible spectroscopy to monitor the full chain backbone alignment, and atomic force microscopy to monitor surface alignment. My graduate mentor and I also employed x-ray photoelectron spectroscopy (XPS) to determine if these polymers vertically phase segregate versus segregate throughout the thickness of the film. The results of this project have clarified the utility of flexible partially conjugated polymers as the matrix in blend systems as well as lead to an understanding of blend morphology for similar components.
Publication Pending.
Molecular origin of strain-induced chain alignment in PDPP-based semiconducting polymers.
In this project, donor-acceptor (D-A) type semiconducting polymers were investigated in order to gain a better understanding of their morphological changes upon mechanical deformation. The Gu research group probed the molecular orientation of diketopyrrolopyrrole (DPP)-based D-A polymer thin films under tensile deformation. We learned that the detailed morphological analysis demonstrated highly aligned polymer crystallites through in-plane rotation, while the degree of backbone alignment was limited within crystalline domains. In this study, I aided in deconvoluting the alignment of different components within the thin-film microstructure by performing peak fitting analysis of X-ray crystallography data. My calculations for the degree of crystallinity for the materials supported my mentor's hypothesis that crystallite rotation and amorphous chain slippage are the primary chain alignment mechanisms for semiconducting polymers.
Spontaneously Supersaturated Nucleation Strategy for High Reproducible and Efficient Perovskite Solar Cells.
Through this collaboration with scientists at Jackson State University, we were able to address the small device size and narrow operation windows which limit the applications for perovskite films predominantly prepared by anti-solvent assisted spin-coating in practical and scalable production. It was my responsibility to study the preferred crystal growth orientation for perovskite films. I performed x-ray scattering analysis on thin film samples and analyzed the inhomogeneous intensity distribution of the scattering rings which could be observed in certain samples. My analysis aided in confirming the reproducibility of highly crystalline perovskite films which were synthesized at Jackson State University. The results of this project suggest that the spontaneously supersaturated nucleation approach holds great potential to the application of scalable solution processing techniques.
Associated Publication: Bo Li, Qiqi Zhang, Song Zhang, Zachary Ahmad, Tamuka Chidanguro, Andrew Hunter Davis, Yoan C. Simon, Xiaodan Gu, Weiwei Zheng, Nihar Pradhan, and Qilin Dai. “Spontaneously Supersaturated Nucleation Strategy for High Reproducible and Efficient Perovskite Solar Cells.” Chemical Engineering Journal. 2021, Volume 405, 126998.
Associated Publication: Qi‐Yi Li, Ze‐Fan Yao, Yang Lu, Song Zhang, Zachary Ahmad, Jie‐Yu Wang, Xiaodan Gu, and Jian Pei. "Achieving High Alignment of Conjugated Polymers by Controlled Dip‐Coating." Advanced Electronic Materials. 2020, no. 6, 2000080.
Achieving High Alignment of Conjugated Polymers by Controlled Dip‐Coating.
The goal of this project was to achieve high polymer chain orientation and ordered thin-film microstructures to allow for efficient charge transport in conjugated polymers. By varying
concentrations during a dip-coating process, we were able to increase the fraction of polymers that adopt planar backbones in accordance with the increase of aggregate size. This work promoted the ensuing assembly process of the polymers and aids the understanding of processing-related parameters in determining morphology of solution-cast thin films. For this project, I used grazing incidence wide-angle x-ray scattering(GIWAXS) to generate 2D images of polymer films, with the incident beam oriented parallelly and perpendicularly to the coating direction. The scattering data highlighted the out-of-plane π–π stacking peaks which shed light onto the morphology of the polymer systems in place. I was also able to generate dichroic ratios via GIWAXS for films deposited at different coating speeds.
Pyrazine-Flanked Diketopyrrolopyrrole (DPP): A New Polymer Building Block for High-Performance n-Type Organic Thermoelectrics.
In this collaborative project with Peking University in China, a new diketopyrrolopyrrole (DPP) derivative was synthesized with the deepest LUMO level of all reported DPP derivatives. The aim of this project was to combat the low electrical conductivities and low thermoelectric power factors that n-doped conjugated polymers usually exhibit. I was tasked with determining the degree of crystallinity and π-π stacking for DPP samples. Through x-ray diffraction analysis, I was able to document the energy loss of ionizing radiation during its travel through the DPP samples and construct a 2D image of the scattering signal. I then generated the appropriate Bragg curves and calculated the degree of crystallinity and π-π stacking, which we used in the publication of the research. Using the data that I generated, my fellow contributors were able to prove that their DPP polymer realizes closer π-π stacking, higher electron mobility, and higher electrical conductivity than previously seen.
Associated Publication: Xinwen Yan, Miao Xiong, Jia-Tong Li, Song Zhang, Zachary Ahmad, Yang Lu, Zi-Yuan Wang, Ze-Fan Yao, Jie-Yu Wang, Xiaodan Gu, and Ting Lei. “Pyrazine-Flanked Diketopyrrolopyrrole (DPP): A New Polymer Building Block for High-Performance n-Type Organic Thermoelectrics.” Journal of the American Chemical Society. 2019, 141 (51), 20215-20221.
