The design of two-dimensional polymers with high stiffness, strength and toughness from monolayer to bulk high-performance films

Two-dimensional (2D) materials have great potential for structural and protective applications due to their incredible mechanical properties, with graphene in particular having the highest tensile stiffness and intrinsic strength measured. However, the same planar sp2-bonded carbon network from which graphene derives its great stiffness and strength also makes it incredibly brittle, thus mitigating the mechanical performance of graphene at larger scales due to the flaw sensitivity of the material. 2D polymers have emerged as an infinitely-tailorable class of materials similar to graphene, with remarkable, tunable mechanical response and density-normalized mechanical properties far exceeding structural materials such as steel, high-performance fibers like Kevlar® or reinforced composites. The U.S. Army Research Laboratory has established a design space for 2D polymers that enables the ground-up design of a high-performance structural film with an unprecedented combination of excellent toughness, stiffness and strength, in scales ranging from monolayer, to few layer to bulk form.
This talk will cover several aspects of 2D polymer research efforts. First, structure-property relationships for 2D polymers will be explored, informing the chemical synthesis of high-performance films of 2D polymers. Using the predicted intrinsic properties, we establish the mechanical theory for a bulk film comprised of an ensemble of finite-sized 2D molecules, and we propose a new, optimal 2D polymer called ‘graphamid’ with a high density of inter-molecular hydrogen bonds to achieve a high-performance membrane with disruptive mechanical potential. Films of 2D polymers downselected from this design space for high tensile properties have been synthesized and mechanically tested, achieving density-normalized modulus and strength comparable to, or exceeding, commercial Kevlar fiber®.

Dr. Sandoz-Rosado is a researcher in the Materials and Manufacturing Sciences Division of the U.S. Army Research Laboratory, and obtained his Ph.D. in Mechanical Engineering from Columbia University where he was a NASA Jenkins Fellow. His current research focuses on the design of 2D polymers and the nanomechanical characterization of 2D materials using both experimental and atomistic simulation techniques, for which he was given the Army Civilian Service Achievement Medal in 2020. Another major area of focus is the characterization of microscale morphologies in high-performance fibers such as ultra-high-molecular-weight polyethylene and Kevlar® to establish structure-property relationships for these soft armor technologies.