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arXiv · 2510.24716

Positive Feedback Drives Sharp Swelling of Polymer Brushes near Saturation

Simon Schubotz·Eva Bittrich·Holger Merlitz·Quinn A. Besford·Petra Uhlmann·Jens-Uwe Sommer·Günter K. Auernhammer
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Abstract

We resolve the Schr\"{o}der paradox for PNiPAAm brushes, showing experimentally that swelling at 100\% relative humidity (RH) matches the liquid state. This occurs via a sharp increase in swelling above 98\%~RH, a behavior standard models fail to explain. Our extended mean-field theory explains this via a positive feedback between swelling and solvent quality, driven by a concentration-dependent $\chi$ parameter. The swelling isotherm quantitatively predicts the dynamic wetting crossover: the advancing contact angle at high velocities drops sharply as ambient humidity surpasses the 98\%~RH threshold.

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Simon Schubotz, Eva Bittrich, Holger Merlitz, Quinn A. Besford, Petra Uhlmann, Jens-Uwe Sommer, Günter K. Auernhammer. 2025-10-28. Positive Feedback Drives Sharp Swelling of Polymer Brushes near Saturation. https://arxiv.org/abs/2510.24716

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