Molecular motion in a spreading precursor film

Spreading of a polymer drop on a solid substrate was monitored with mol. resoln. Three characteristic rates, i.e., the spreading rate of the precursor film Dspread=(3.9±0.2)×103 nm2/s, the flow-induced diffusion rate of mols. within the film Dinduced=1.3±0.1 nm2/s, and the thermal diffusion coeff. of single mols. Dtherm≤0.10±0.03 nm2/s, were independently measured. Since Dspread»Dinduced, the plug flow of polymer chains was identified as the main mass-transport mechanism of spreading with an insignificant contribution from the mol. diffusion. [on SciFinder(R)]