Controlling the force range of polymeric force sensors made from rationally designed mechanochromic copolymer networks

This proposal is concerned with the development of a novel concept of mechanochromic polymeric materials exhibiting a controllable force range. Based on main chain spiropyran elastomeric networks made by acyclic diene metathesis polymerization and dithiol-ene cross-linking, we will design, synthesize and characterize different materials in which different levels of stress will cause the spiropyran (SP, colorless)-merocyanine (MC, colored) transformation. This will be enabled by varying substituents, polymer chain linkage, and glass transition temperature, all of which alter the activation energy needed for the mechanically-induced SP-MC isomerization and the efficacy of mechano-transduction. To understand the fundamentals of this isomerization in detail and to guide syntheses, density functional theory calculations will be carried out in parallel. On the one side this will lead to a deep understanding of the mechanically-induced SP-MC isomerization, and on the other side reduce the amount of synthetic work. Mechanical experiments with in-situ spectroscopies (UV-vis, dielectric) will be performed to demonstrate the force-sensing capabilities of on the novel elastomers as a function of the applied load. This project will overcome one of the most critical obstacles that limit a broader use of mechanochromic reactions in polymeric force sensors.

DFG Programme Research Grants

Co-Investigator Professor Dr. Christian Friedrich