DYNAMICS OF SPREADING OF LIQUID MICRODROPLETS ON SUBSTRATES OF INCREASING SURFACE ENERGIES

By spatially resolved single-wavelength ellipsometry, we investigate t he spreading on a solid substrate of low molecular weight trimethyl-te rminated poly(dimethylsiloxane) droplets. Especially, we focus our stu dy on the dependence of the diffusion coefficient of the first molecul ar layer on the substrate surface energy, characterized by the critica l surface tension gamma(c) measured for the alkane series. Our experim ental data show that the diffusion coefficient D calculated from the f ilm length reaches a maximum value for surfaces of intermediate energi es. This result is shown to be consistent with the predictions of the available theoretical approaches and agrees quite well with molecular dynamics simulations reported in the third part of the paper.