Beyond confinement: conformational memory and the continuing legacy of Reiter and de Gennes in polymer films

Polymer films exhibit behaviour that cannot be explained by confinement effects alone. In 2001, Reiter and de Gennes proposed an alternative perspective, suggesting that preparation stages can imprint a form of conformational memory in polymer films. According to this view, polymers inherit nonequilibrium conformations during preparation, and the subsequent relaxation of this memory proceeds through a cascade of metastable states. This concept provided a rationale for several unusual behaviour, most notably the negative thermal expansion observed in freshly cast polymer films. Over the past two decades, experimental studies have accumulated strong evidence for preparation-induced conformational memory, often manifested through residual stresses and their slow relaxation. These advances have begun to establish preparation as a quantitative lever for probing nonequilibrium polymer physics. Despite this progress, several fundamental questions remain unanswered. In this article, I revisit the work of Reiter and de Gennes and summarize key experimental developments, emphasizing their continuing legacy. I will conclude by highlighting open questions whose answers would not only improve our fundamental understanding but also bring us closer to exploiting preparation as a quantitative lever to design programmable materials.