Linking acoustic waves and polymer deformation to reveal energy transmission pathways.

From fundamental understanding of materials to biology to communication and sensing, acoustic waves represent the primary means for mechanical information and energy to flow through matter. While traditionally used to access the physical properties of materials, exactly how acoustic waves relate to molecular-level perturbations, including nonlinear processes, remains unanswered. Here, we study this question by conducting atomic simulations of a nanostructured elastomeric block copolymer subjected to a nanoscopic perturbation at rates below and above the acoustic properties of the material. We find that the mode of energy propagation and dissipation transitions from a material-deformation-defined response at slow perturbations, to an inertia-dominated response at fast perturbations. Notably, the results reveal that the crossover depends on propagation of the slow extensional wave, as opposed to the propagation of the fast longitudinal wave traditionally believed to dictate energy flow in materials, and emerges from polymer chain-level dynamics. These insights collectively demonstrate a mechanistic relationship between molecular response and wave propagation, opening new ways to design, study, and manipulate materials with implications spanning mechanical computation to hypersonic impact.