Unravelling Popular Myths in the Rheology of Entangled Polymer Melts

\underline {Myth No 1}: \textbf{Constraint release and Chain End Fluctuation} coupled with Reptation dominate stress relaxation of highly entangled chains. Fact: Experiments show that Percolation processes account for about 50{\%} of the relaxation, coupled with deGennes Reptation dynamics. In fact, the random coils are not relaxed (via Neutrons) when the stress (Birefringence) goes to zero, a critical prediction of the percolation mechanism, which is not in violation of the stress-optical law.. \underline {Myth No 2}: The \textbf{Packing Length Entanglement Model }for the critical entanglement molecular weight, M$_{\mathrm{e}} =$ 354 p$^{3}$, provides a fundamental description of entanglements at the molecular level. Fact: Experiments show that the Packing Length model is fundamentally incorrect in all its predictions of rheological properties via M$_{\mathrm{e}}$ $\sim$ [ M$_{\mathrm{o}}$/C$_{\mathrm{\infty }}$]$^{\mathrm{3}}$, especially at the nanoscale, as well as the bulk. This is due to an incidental relationship between the monomer molecular weight M$_{\mathrm{o}}$ and the characteristic ratio C$_{\mathrm{\infty }}$ for vinyl type polymers. The correct entanglement model is given by M$_{\mathrm{e}}$ $\sim$ C$\infty $M$_{\mathrm{o}}$. \underline {Myth No 3}: \textbf{The Glass Transition T}$_{\mathrm{\mathbf{g}}}$\textbf{ is dominated by Segmental Dynamics and Free Volume}: Fact: Experiments show that T$_{\mathrm{g}}$ is dominated by the cluster dynamics of anharmonically interacting fractal aggregates which range from 1-100 nm in size (ave $\sim$ 5 nm), as described by the TFT. In nanoconfined thin films, the segmental dynamics does not change much while huge decreases in T$_{\mathrm{g}}$ can be observed due to cluster size effects.