Exploring conditions for craze initiation and for absence of crazing in polymer glasses

Although crazing in polymer glasses has been extensively studied in the past, it is still difficult to predict and explain when and why crazing would take place. There is even a recent proposal to suggest [1] that craze initiation is ``a frustrated fracture process than rather a yield mechanism'' [2]. In this work, we report the variable parameters that influence crazing. Specifically, we show that a ``young'' glass (prepared by mechanical ``rejuvenation'') can resist crazing and aging promotes crazing. Thus, the degree of vitrification is one variable. Under creep, crazes form faster at a higher tensile stress, showing that crazing is an activation process and depends on the external condition. We also show how the large-scale structure such as the degree of chain networking affects crazing behavior. For example, melt stretching suppresses crazing. Finally, we demonstrate crazing in absence of any ongoing extension when a cold-drawn polymer glass is held fixed when annealing well below T$_{\mathrm{g}}$ during the elastic yielding [3]. These new observations have inspired a molecular picture for large deformation of polymer glasses [4]. \\[4pt] [1] \textit{Polymer }2007\textbf{,} \textit{48}, 1030;\\[0pt] [2] \textit{Polymer }2011\textbf{,} \textit{52}, 2319;\\[0pt] [3] \textit{Phys. Rev. Lett. }2013, \textit{110}, 065506;\\[0pt] [4] submitted to Polymeric Glasses session.