Molecular Weight Dependence of Spreading Rates of Ultrathin Polymeric Films

Details Molecular Weight Dependence of Spreading Rates of Ultrathin Polymeric Films Molecular Weight Dependence of Spreading Rates of Ultrathin Polymeric Films

1998-04-24

arxiv.org/abs/cond-mat/9804270v1

PRL 80, 5377 (1998)

Physics

Condensed Matter

Soft Condensed Matter

4 pages, 2 figures, to appear in PRL

Scientific paper

10.1103/PhysRevLett.80.5377

We study experimentally the molecular weight $M$ dependence of spreading rates of molecularly thin precursor films, growing at the bottom of droplets of polymer liquids. In accord with previous observations, we find that the radial extension R(t) of the film grows with time as R(t) = (D_{exp} t)^{1/2}. Our data substantiate the M-dependence of D_{exp}; we show that it follows D_{exp} \sim M^{-\gamma}, where the exponent \gamma is dependent on the chemical composition of the solid surface, determining its frictional properties with respect to the molecular transport. In the specific case of hydrophilic substrates, the frictional properties can be modified by the change of the relative humidity (RH). We find that \gamma \approx 1 at low RH and tends to zero when RH gets progressively increased. We propose simple theoretical arguments which explain the observed behavior in the limits of low and high RH.

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