Meaning
Polymer physics frameworks simulate the non-linear rheological response of branched molecular architectures by representing a central backbone segment terminated by multiple arm branches at each end. When applied to low-density polyethylene and long-chain branched polymers, the pom-pom model captures both shear thinning and extensional strain hardening simultaneously. The central backbone experiences orientation and stretching, while the dangling arms provide entropic resistance that retards relaxation.
Separation of stretch and orientation relaxation times allows independent modeling of shear and extensional flow behaviors. The mathematical formulation assumes idealised symmetric branching and loses accuracy in randomly branched polydisperse polymer melts.
Branch Architecture
Structural parameters in the model define the number of arm branches and the ratio of backbone length to arm length. In low-density polyethylene melt characterization, the pom-pom model accounts for branch point withdrawal into the backbone tube under severe extensional flow. Molecular branch density determines the magnitude of strain hardening observed during high-speed processing steps.
Stretch Dynamics
Backbone stretching occurs only when extensional rates exceed the reciprocal of the backbone stretch relaxation time. Dynamic equations inside the pom-pom model bound the maximum backbone stretch by the number of arm branches available to generate tension. When maximum stretch is reached, arm withdrawal occurs and the material exhibits extensional softening.
Viscoelastic Limit
Extensional viscosity predictions from the model feed directly into finite element software for moulding and extrusion process simulation. Discrepancies emerge in complex industrial flows where polydispersity produces a wide spectrum of molecular relaxation times. Multi-mode variations of the pom-pom model address broad molecular weight distributions by combining multiple branch structures in parallel.
