https://doi.org/10.1140/epje/s10189-025-00547-7
Perspective - Soft Matter
Projecting dynamic heterogeneity into nanoconfinement: the enduring legacy of the Long–Lequeux model
Polymer and Soft Matter Dynamics, Experimental Soft Matter and Thermal Physics (EST), Université libre de Bruxelles (ULB), 1050, Brussels, Belgium
Received:
2
December
2025
Accepted:
8
December
2025
Published online:
26
December
2025
In the early 2000s, Long and Lequeux established the first quantitative link between dynamic heterogeneity in the bulk and shifts in the glass transition temperature 
of thin films. Their minimal mean-field model demonstrated that equilibrium density fluctuations give rise to nanometric slow domains, the percolation of which governs vitrification. By showing how geometrical confinement alters this percolation pathway, they predicted shifts using only bulk properties, without fitting interfacial parameters. This conceptual breakthrough, in which finite-size effects emerge from projecting bulk dynamic heterogeneity onto a restricted geometry, constitutes the enduring legacy of their work. Subsequent experiments have confirmed this picture, showing that depression in free-standing films scales with the thickness of a liquid-like surface layer, while in supported systems mobility gradients reflect the reorganization of slow domains anchored at the interface. Looking forward, I outline at the end of this perspective several possible directions for refining this framework so as to capture a broader spectrum of relaxation channels, thereby enriching our understanding of dynamics in both bulk and confined polymer melts.
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Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
