Browsing by Author "Fang, Lei"

Now showing 1 - 3 of 3

CAREER: Conformational Control of pi-Conjugated Polymeric Materials Through Dynamic Bonds
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/236; National Science Foundation
NON-TECHNICAL SUMMARY This project aims to investigate the fundamental correlation between the geometry of electrically semiconducting polymer molecules and their corresponding materials properties. Most polymeric molecules possess structural flexibility at the nanometer and subnanometer scales, which leads to various 3D shapes that they can adopt. Such geometric variability impacts a wide range of polymer properties that are important for their applications, especially those related to electronic and optical properties. Precision control of the molecular shapes of semiconducting polymers, however, has been a long-standing scientific challenge. This CAREER project tackles this problem by synthesizing molecules with reversible and controllable interactions between different segments along the polymer chain. Through this approach, planarized geometries of these polymer molecules can be enforced and disrupted on demand, leading to tailored properties as a result of the switchable molecular shapes. Establishment of this structural control may not only enable the access of improved functional performance, but also allow for feasible processing of polymer materials into application-relevant forms. In addition, the knowledge gained in this project will advance fundamental understanding in materials-related sciences and benefit multiple research disciplines and STEM education. The educational component of this program focuses on connecting scientific concepts and real-world personal knowledge for the students through relevant experiments in the lab and immersive learning experiences. The societal impacts of this project include benefits from scientific publications, new course components, educational software, and trained STEM students for academia and industry. TECHNICAL SUMMARY This program integrates research, education, and outreach activities under the overarching theme of functional polymer materials. Through a synergistic approach combining chemical synthesis, process engineering, and materials characterization, the research project seeks to establish clear fundamental correlations between controlled torsional conformation and materials properties of pi-conjugated systems. This plan is driven by the underlining hypothesis that active control over torsional conformation can significantly impact polymer properties and processability. The key strategy to achieve this objective is the incorporation of controllable intramolecular dynamic bonds into polymer backbones. A systematic design principle to the synthesis and process engineering of such polymers will be developed on the basis of theoretical simulations and experimental feedback. Structure-property relationships of these materials will be investigated through iterative design-test-feedback-optimization cycles. The ultimate goal is to draw a clear structure-property correlation and to establish design principles for tailoring the integrated properties of conjugated polymeric materials. In parallel, educational and outreach activities are planned to enhance chemistry and broad STEM learning outcome synergistically with the research program. The pedagogical focus is to make the essential connections between scientific knowledge and real-life experiences for the next generation of STEM students through an integrated plan combining course development, undergraduate research programs and outreach activities.
Collaborative Research: Synthesis and Rigidity Quantification of Ladder Polymers with Controlled Structural Defects
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/236; National Science Foundation
With funding from the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division, Professors Lei Fang of Texas A&M University and Xiaodan Gu of University of Southern Mississippi are investigating how chain flexibility influences the physical properties of conjugated ladder polymers. Conjugated polymers are a unique class of non-metallic polymers with semiconducting properties resembling that of the chemical element silicon. These long chain carbon-based molecules can become conductive when external voltage is applied (like in transistors) or light shines on them (like in photovoltaic cells). Conjugated polymers are extensively used in solar cells, LED screens and other applications that utilize the conversion of electricity to light. Ladder polymers, on the other hand, are a type of double stranded polymers with the connectivity of a ladder. This is achieved by interconnecting repeating units along the main polymer chain by four chemical bonds, instead of the two bonds typically seen in conventional plastics. In this research, conjugated ladder polymers with varied structural features are synthesized. Control polymers are prepared with deliberately introduced backbone defects that consist of small molecules. Detailed studies are then conducted to correlate backbone composition and length with the flexibility of the polymer chains. These studies are enabled by employing neutron and light scattering techniques which provide accuracy at lengths ranging from sub 1 nanometer (1/100,000 of human hair diameter) to well beyond 10 micrometers (the width of cotton fiber). Correlations established as a result of this work may provide knowledge that could lead to the development of materials with better optical and electronic performance. Educational innovation tackles the problems associated with outdated contents in undergraduate organic chemistry laboratory courses. The newly designed ?Nobel Prize Reactions? are first implemented at both universities and then disseminated at national and international scales. Outreach activities expose undergraduate and high school students to modern chemical research. This work is specifically designed to benefit a large number of underrepresented minorities and economically disadvantaged students in Mississippi. The primary goal of this research is to establish the fundamental correlations between backbone constitution and the chain rigidity for rigid ladder conjugated polymers. The research is conducted through the design and synthesis of model ladder polymers with varied structural features, and controls with deliberately introduced backbone defects, followed by quantitative evaluation of their chain persistence length and correlation with structural features. Chain rigidity of the ladder polymer models and controls is quantified using combined modern characterization tools with an emphasis on neutron and light scattering. Studies are also performed to understand the influence of chain bending energy on persistent length for ladder polymers. Comprehensive structural-rigidity correlation through iterative design-synthesis-measurement-design cycles is established. Results associated with this award have the potential to advance knowledge on how the chain rigidity (or flexibility) determines the fundamental properties and practical applications of a wide range of polymers. 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.
Collaborative Research: Synthesis and Rigidity Quantification of Ladder Polymers with Controlled Structural Defects
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/236; National Science Foundation
With funding from the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division, Professors Lei Fang of Texas A&M University and Xiaodan Gu of University of Southern Mississippi are investigating how chain flexibility influences the physical properties of conjugated ladder polymers. Conjugated polymers are a unique class of non-metallic polymers with semiconducting properties resembling that of the chemical element silicon. These long chain carbon-based molecules can become conductive when external voltage is applied (like in transistors) or light shines on them (like in photovoltaic cells). Conjugated polymers are extensively used in solar cells, LED screens and other applications that utilize the conversion of electricity to light. Ladder polymers, on the other hand, are a type of double stranded polymers with the connectivity of a ladder. This is achieved by interconnecting repeating units along the main polymer chain by four chemical bonds, instead of the two bonds typically seen in conventional plastics. In this research, conjugated ladder polymers with varied structural features are synthesized. Control polymers are prepared with deliberately introduced backbone defects that consist of small molecules. Detailed studies are then conducted to correlate backbone composition and length with the flexibility of the polymer chains. These studies are enabled by employing neutron and light scattering techniques which provide accuracy at lengths ranging from sub 1 nanometer (1/100,000 of human hair diameter) to well beyond 10 micrometers (the width of cotton fiber). Correlations established as a result of this work may provide knowledge that could lead to the development of materials with better optical and electronic performance. Educational innovation tackles the problems associated with outdated contents in undergraduate organic chemistry laboratory courses. The newly designed ?Nobel Prize Reactions? are first implemented at both universities and then disseminated at national and international scales. Outreach activities expose undergraduate and high school students to modern chemical research. This work is specifically designed to benefit a large number of underrepresented minorities and economically disadvantaged students in Mississippi. The primary goal of this research is to establish the fundamental correlations between backbone constitution and the chain rigidity for rigid ladder conjugated polymers. The research is conducted through the design and synthesis of model ladder polymers with varied structural features, and controls with deliberately introduced backbone defects, followed by quantitative evaluation of their chain persistence length and correlation with structural features. Chain rigidity of the ladder polymer models and controls is quantified using combined modern characterization tools with an emphasis on neutron and light scattering. Studies are also performed to understand the influence of chain bending energy on persistent length for ladder polymers. Comprehensive structural-rigidity correlation through iterative design-synthesis-measurement-design cycles is established. Results associated with this award have the potential to advance knowledge on how the chain rigidity (or flexibility) determines the fundamental properties and practical applications of a wide range of polymers. 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.