Real-Time Quantification of Molecular-Level Dynamic Behaviors Underpinning Shear Thinning in End-Linked Associative Polymer Networks.

Shear thinning of associative polymers is tied to bond breakage under deformation and retraction of dangling chains, as predicted by transient network theories. However, an in-depth understanding of the molecular mechanisms is limited by our ability to measure the molecular states of the polymers during deformation. Herein, utilizing a custom-built rheo-fluorescence setup, bond dissociation in model end-linked associative polymers is quantified in real time with nonlinear shear deformation based on a fluorescence quench transition when phenanthroline ligands bind with Ni.

Reactivity-Guided Depercolation Processes Determine Fracture Behavior in End-Linked Polymer Networks.

The fracture of polymer networks is tied to the molecular behavior of strands within the network, yet the specific molecular-level processes that determine the mechanical limits of a network remain elusive. Here, the question of reactivity-guided fracture is explored in otherwise indistinguishable end-linked networks by tuning the relative composition of strands with two different mechanochemical reactivities. Increasing the substitution of less mechanochemically reactive ("strong") strands into a network comprising more reactive ("weak") strands has a negligible impact on the fracture energy until the strong strand content reaches approximately 45%, at which point the fracture energy sharply increases with strong strand content.

Use of a Modified SIRD Model to Analyze COVID-19 Data.

Since the starting of the year 2020, the whole world is facing a challenge due to an outbreak of an unprecedented COVID-19 pandemic owing to a novel coronavirus. Here, a modified susceptible-infected-recovered-dead model has been used to analyze the time series data of the pandemic for five countries. It is established that the present model is capable of simultaneously explaining the temporal evolution of active-infected, recovered, and dead population of all these five countries.