Effective removal of entanglement points by network dilution

A polymer system in which the chains are much longer than the entanglement molecular weight, $M_{+} \gg M_{e}$ is well entangled. When a thin polymer film is uniaxially strained below the glass transition temperature crazes are formed. Measurements of the volume fraction of the deformed versus the undeformed regions can give information on the entanglement density of the system\footnote{ACM Yang, EJ Kramer, CC Kuo, SL Phoenix, \emph{Macromolecules} \textbf{19} 2020 (1986)}. We present results of such deformation experiments, probed using atomic force microscopy, in which well entangled networks have been diluted with chemically identical species of molecular weight, $M_{-}< \sim M_{e}$ which results in a decrease in the entanglement density. Varying the length of the diluent chains provides molecular information on how the entanglement network is swelled.