Dewetting is the process that is the reverse of wetting, in which a film of fluid tends to transform from a film to droplets. This is a phenomenon that is common in daily life, such as painting, lubrication and coating. Our group had established a new method for introducing dewetting on polymer film via microwave irradiation, which can generate nano-scale dewetting droplets (...[ Read more ]

Dewetting is the process that is the reverse of wetting, in which a film of fluid tends to transform from a film to droplets. This is a phenomenon that is common in daily life, such as painting, lubrication and coating. Our group had established a new method for introducing dewetting on polymer film via microwave irradiation, which can generate nano-scale dewetting droplets (<100nm in diameter) in a very short heating time (15min).

In this study, a hypothesis of the microwave induced dewetting mechanism was proposed and examined. The microwave irradiation was proposed to introduce local heating at the polymer-substrate interface. The presence of local heating will speed up the oxidation of polymer during the treatment. The interfacial energies of the system will be changed so that some stable systems can undergo dewetting by microwave treatment.

The interfacial energies of different systems were first determined by contact angle analysis and the use of the three liquid method. After that, the spreading coefficients of different systems were calculated. By considering the spreading coefficients, chemical changes were shown to occur during the microwave treatment.

ToF-SIMS analysis was performed and the results show that oxidation really occurred during the microwave treatment and local heating was generated in the polymer-substrate interface.

Finally, microwave treatment and hydrothermal treatment were compared in order to determine the effect of microwave irradiation and the presence of water separately. The result shows that the microwave radiation will generate local heating and speed up the dewetting process while the dewetting is mainly driven by the presence of water due to the change in surface energies of the systems.