Pinching Dynamics of Telechelic Associating and Coupling Polymers

Telechelic associating polymers, TAPs, have numerous industrial applications and are typically evaluated at different concentrations and by their shear viscosity. Here, in situ UV irradiation is added to a dripping-onto-substrate rheometer. TAPs with telechelic coumarin end groups would undergo UV-induced coupling, leading to additional step polymerization of TAPs. This enables us to in situ increase the molecular weight of TAPs without changing concentrations. Their extensional rheology is studied from the recorded pinching process. Extensional viscosities in the elastocapillary state are 10 times higher than those in the viscocapillary state, indicating significant chain stretching. With increasing molecular weights or degrees of coupling, the evolution of capillarity, inertia, viscous, and elastic behaviors is captured by the dimensionless Ohnesorge number and intrinsic Deborah number. The narrow region of a beads-on-a-string structure is also mapped experimentally. Using telechelic associating and coupling polymers as a model system, we have illustrated the evolution of their extensional behaviors as the molecular weight increases.