MECHANISMS OF ELASTICITY IN SEMICONDUCTING POLYMERS
Abstract
There are many types of conventional polymers and engineering plastics that display exceptional robustness against mechanical insults, such as scratching, indentation, and delamination. Chief among these materials include the polymers used in car paint, road surfaces, optical coatings, and biomedical implants. In the field of ?-conjugated (semiconducting) polymers—in which devices are expected to find use in mechanically demanding applications in aerospace, nautical, and wearable contexts—the emphasis in the last several year has been to increase the softness. That is, the stretchability, elasticity, and toughness. However, ease of deformability is not the right property for many distributed systems at risk of mechanical damage. Examples of these distributed applications include ultra-lightweight solar panels for UAVs and spacecraft, biomedical sensors integrated with flight suits, and instrumented aircraft surfaces. These applications instead require hardness, strength, and resilience. The goal of this proposal is thus to increase the robustness of materials and devices used in organic electronic and bioelectronic devices against mechanical damage. Our approach encompasses theory informed by computation, chemical synthesis, and processing. In this proposal, each of three research thrusts seeks to understand the design criteria for semiconducting polymers that have mechanical properties characteristic of protective polymeric coatings. We will begin by reconceptualizing the fundamental parameters which govern molecular flexibility for semiconducting polymers (Thrust 1). In particular, we will incorporate the effects of electron delocalization and out-of-plane dihedral torsion on the flexibility of polymer chains. We will then use molecular dynamics simulations to understand deformation of ordered domains in solid films, and use reactive force fields that allow for scission of bonds under mechanical loading. This basic, hypothesis-driven research will be supported by molecular design and synthesis (Thrust 2) that should increase the hardness of the solid films of conjugated polymers without sacrificing the charge-transport properties. The molecular designs proposed in this thrust are based on (i) our computational results, (ii) motifs found in polymers designed for hardness (i.e., engineering plastics), and (iii) knowledge we have produced while engineering conjugated polymers for increased softness. In Thrust 3, we will use a variety of approaches for mechanical characterization to validate the hypotheses posed in Thrusts 1 and 2. Complementing these approaches—many of which were developed in our laboratory—is a new method of processing called solid-phase deposition (SPD). This process takes advantage of deformation and post-deposition hardening to form optoelectronic coatings on a variety of surfaces, including textured, multilayer, and composite structures.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 20, 2023
- Source ID
- FA95502210454
Entities
People
- Darren J. Lipomi
Organizations
- Air Force Office of Scientific Research
- United States Air Force
- University of California, San Diego