Pure and Applied Chemistry

Abstract: One of the least understood and least exploited aspects of nanoscience is dynamic coupling between directional translation at mesoscales (lengths above ~50 nm) and changes in local chemical bonding (lengths below ~1 nm). A major cause is the traditional dominance of two distinct and seemingly incompatible models for describing dynamics at the two scales: continuum mechanics based on the balance of forces, i.e., mechanical equilibrium (lengths above ~50 nm) and activated escape from an energy well, i.e., chemical equilibrium (below ~1 nm). These models yield meaningful results within their respective dimensional limits but leave processes in between in the gray area of conceptual ambiguity and technical intractability. Such processes underlie phenomena as diverse as catastrophic failure of strained materials, operation of motor polymers, behavior of polymer flows, and mechanosensing. Chemomechanics integrates the two conventional dynamic models into a single internally consistent, scale-independent framework that is essential for a quantitative understanding and the efficient exploitation of dynamic coupling across the “formidable gap” at ~1–50 nm. Chemomechanics holds promise (1) to facilitate significantly the design of new stress-responsive and actuating polymers, including those optimized specifically for the propulsion of autonomous nanomechanical devices and for use in micro- and nanoscale stress sensors; and (2) to yield general predictive molecular relationships between chemical composition, structure, and mechanical properties of polymers both at the single-chain and bulk levels. Theoretical and experimental studies of dynamic coupling across the formidable gap have traditionally been carried out within soft-matter physics. As far as I am aware, my group was the first to approach the problem from a chemist’s perspective. Below, I summarize the state-of-the-art of chemical understanding of processes in the formidable gap from both theoretical and experimental perspectives.