Possible explanation of the Lambda-shape anomaly in polymer surface diffusion.
We suggest an explanation for the anomalous behavior of the polymer surface-diffusion coefficient D reported by Zhao and Granick [J. Am. Chem. Soc. 126, 6242 (2004)]: D first increased with increasing polymer surface concentration Gamma, then suddenly dropped at a threshold value Gamma*. Our molecular dynamics simulations show the same behavior. We find that polymers form single-layered pancake structures for Gamma Gamma*. The double-layer structures allow the polymers to better adapt to the substrate corrugation. This increases barriers for lateral diffusion and is thus consistent with small values of D at larger Gamma.
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