Melting and Crystallization of Poly(ethylene oxide) Nanofilms Studied by Micromechanical Cantilevers

Abstract

Melting and crystallization of thin poly(ethylene oxide) (PEO) films are studied by micromechanical cantilevers (MC) consisting of a micromachined silicon substrate with native oxide layer and a thin poly(ethylene oxide) coating. Phase transitions of the PEO nanofilms, such as melting and crystallization, appear as signals in the temperature-dependent deflection traces. The melting temperature (Tm) of thin films with thickness of 20–700 nm measured by MC is about 7–10 K lower than that of bulk samples measured by differential scanning calorimetry (DSC) due to the size effect and different crystallization conditions. However, the crystallization temperature (Tc) obtained by MC and DSC is almost the same. Both Tm and Tc measured by MC increase with increasing film thickness. Besides, both Tm and Tc decrease with increasing number of heating–cooling cycles due to partial dewetting of the polymer films from the silicon oxide substrate surface, which results in a decreased contact area and adhesion strength at the interface.