Physics
Dewetting of Polymer Films
Dewetting is a phenomenon in which a liquid film of uniform thickness on a non-wetting substrate surface breaks up and develops into liquid beads. In some sense, this process can be viewed as a phase separation process, wherein a homogeneous polymer film phase separates into regions deficient of the polymer (i.e. holes) and regions rich in the polymer (i.e. polymer beads). Though simple as this analogy may sound, for a decade opinions have been divided between spinodal instability (which is tie to an unstable system) and heterogeneous nucleation (tie to a metastable system) being the major cause of the instability. We devise experiments to be able to make the distinction unambiguously and hence delineate applicability of the classical linear theory of spinodal decomposition in regimes close to metastable regions.
Besides studying the fundamentals, we also explore possibilities to make use of this spontaneous dewetting process to make useful mesoscopic structures in large areas. Figure 1 shows one kind of pattern that can be made by using this approach. It is interesting to note that the pattern contains features of sub-micron sizes. Normally, to make features with such sizes will require sophisticated techniques such as photo- or e-beam lithography. But with our approach, it is as simple as roasting the sample on a hot plate for a few minutes.