Modeling and Design of Self-Healing Multifunctional Networks from Polyphilic Oligomers

Cornell University, Ithaca NY

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports research and education in the fields of computational modeling and materials engineering. Materials that exhibit properties intermediate between typical liquids and typical solids are important for numerous applications. Examples of such multipurpose materials include rubbers, liquid-crystals, and glasses. Having a dual character with some specific combination of solid-like and liquid-like features is instrumental to their enhance functionality in such applications as shock absorbers, electronic displays, specialty glues, packaging, etc. The challenge tackled in this project is the design of materials that possess a solid-like high mechanical strength, but also a liquid-like plasticity to allow for significant extent of self-healing after large deformations. This type of material fills a different region of the intermediate solid-like/liquid-like property space which more conventional materials already occupy. The proposed materials will be designed to have high toughness and self-healing abilities by virtue of using small-molecule building blocks, the presence of solid-like and liquid-like inter-penetrating regions, and an imprintable ‘shape’ memory arising from tunable bonds. Such materials can find potential applications as shock absorbers, mechanical cloaking devices, flexible semiconductors, and biomimetic materials like artificial cartilage and bone. Resilience and self-healing properties allow materials to have longer service lives and lower user demands, thus potentially reducing their associated manufacture costs and carbon footprint. This project will use molecular modeling methods to establish correlations between the structure and mechanical properties of this type of material and is complementary to experimental efforts by Cornell research groups involved with designing new organic materials. The project will enable the training of a doctoral student and an undergraduate student in computational materials research. Relevant results will be disseminated through multiple forums including Cornell’s Soft Matter seminar series, professional meetings, and will contribute to a hands-on lab (about ‘Engineering liquid-like solids and solid-like liquids’) for the Women’s group outreach initiative in the Chemical Engineering Department that targets rural High School girls. TECHNICAL SUMMARY This award supports research and education in the fields of computational materials science and soft matter engineering. The overarching goal of the project is to predict how polyphilic molecules assemble into percolating mesophases having solid-like and liquid-like domains so that upon crosslinking they can encode a structural memory that endows them with the ability to both absorb the stress of large strain deformations and to self-heal. Such materials lie in the design space between small-molecule frameworks and macromolecular networks, and are envisioned to have solid-like mechanical strength and liquid-like reconfigurability. The building blocks of interest are polyphiles having different blocks whose lack of mutual affinity leads to ordered nano-segregated percolating structures with solid-like frameworks filled by amorphous channels. Rigid aromatic blocks are suitable to form the framework struts, polar hydrogen-bonding moieties are suitable to glue the struts into percolating patterns, and flexible side chains of hydrophobic segments can be added as structure-directing agents to modulate the framework geometry. While the self-assembled ordering (and associated hydrogen bonding) encodes a soft physical ‘memory’ for the material to recover its structure upon deformation, the project explores the use of crosslinking of the pre-assembled structures as a strategy to imprint a tunable, more permanent chemical memory. Molecular dynamics simulations using both coarse-grained and atomistic models will be used to investigate: (1) The tensile deformation of linear crosslinked triblock oligomeric systems preassembled into lamella mesophases as the baseline for understanding the correlation between stress response and mechanisms of molecular deformation, nano-phase transitions, and hysteresis, (2) how physical and chemical modifications of the triblock can tune the tensile response of lamellar-preassembled crosslinked networks, and (3) the tensile deformation behavior of crosslinked, branched polyphiles preassembled into phases other than the lamellar phase, particularly, of network phases like the diamond and gyroid. The project will provide a framework to train a doctoral student and an undergraduate student in the areas of computational multiscale modeling, statistical mechanics, and soft matter science. This project will also strengthen collaborations with Cornell research groups involved with designing new organic materials. Results will be disseminated primarily through professional meetings and will contribute to the creation of new teaching material and outreach activities in the Department. STATEMENT OF MERIT REVIEW 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.