Strain‐Induced Density Fluctuations in Glassy Polymers

Deformation of glassy polymers induces plastic flow as a result of mechanical instability, ultimately leading to cavitation and fracture of the liquid. Thus, understanding the origin of such mechanical instability is crucial. Here, we demonstrate that strain deformation of polymeric glass is accompanied by marked shear‐thinning behavior and leads to enhanced density fluctuations. These results are consistent with Furukawa and Tanaka's theory, which predicts that strain induces the self‐amplification of the density fluctuations. Thus, we conclude that the enhancement results from the coupling between the velocity field and density fluctuations, stemming from the Furukawa and Tanaka theory, glassy polymer, small‐angle X‐ray scatteringstrong density dependence of viscosity.