Residual stresses in thin polymer films cause rupture and dominate early stages of dewetting

Abstract

In attempting to reduce the size of functional devices, the thickness of polymer films has reached values even smaller than the diameter of the unperturbed molecule. However, despite enormous efforts for more than a decade1, our understanding of the origin of some puzzling properties of such thin films is still not satisfactory and several peculiar observations remain mysterious. For example, under certain conditions, such films show negative expansion coefficients2,3,4,5,6 or show undesirable rupture although energetically they are expected to be stable7. Here, we demonstrate that many of these extraordinary effects can be related to residual stresses within the film, resulting from the preparation of these films from solution by fast evaporation of the solvent8. Consequently, depending on thermal history and ageing time, such films show significant changes even in the glassy state9,10, which we quantify by dewetting experiments and corresponding theoretical studies. Identifying the relevance of frozen-in polymer conformations gives us a handle for manipulating and controlling properties of nanometric thin polymer films.

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Figure 1: Influence of ageing on the probability for film rupture, expressed by means of the areal density of holes.
Figure 2: The shape of the rim during early stages of dewetting of thin polymer films on non-adsorbing substrates.
Figure 3: Typical results for dewetting of PS thin films on a non-adsorbing substrate.
Figure 4: The influence on dewetting of storing (ageing) PS films for increasing times below the glass-transition temperature.

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Acknowledgements

This work was supported by the Belgian National Fund for Scientific Research (FNRS), the Research Ministry of the Walloon Region and the Social European Fund. Pascal Damman is a Research Associate of the FNRS. Both teams from France acknowledge financial support from the European Community’s ‘Marie-Curie Actions’ under contract MRTN-CT-2004-504052 [POLYFILM].

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Correspondence to Günter Reiter.

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Reiter, G., Hamieh, M., Damman, P. et al. Residual stresses in thin polymer films cause rupture and dominate early stages of dewetting. Nature Mater 4, 754–758 (2005). https://doi.org/10.1038/nmat1484

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