Relaxation of stored mechanical stress along chemical reaction pathways

Abstract

Mechanical stress induced in a condensed material relaxes by way of viscous flow, that is by slippage of neighbouring molecules past each other and by the frictional dissipation into heat of the potential energy between them. We show here that this is not necessarily the only way by which energy of deformation can be dissipated. The breaking of chemical bonds within mechanically stressed molecules participating in a chemical reaction provides an alternative and parallel pathway for relaxation and is thus a factor in rheological description which has not been adequately recognized. A chemical change not only alters the composition of the system, and thus the response of its material, but also directly modifies the time scale of the relaxation modes of the molecules participating in the reaction. The involvement of chemical reactions in rheological processes has very broad implications, as most real systems—certainly all living systems—undergo chemical changes, although the rates of these may vary considerably.