Inhibition of the crystallization in nanofilms of poly(3-hydroxybutyrate)

The aim of this work is to obtain amorphous thin films of poly(3-hydroxybutyrate) (PHB) at room temperature. The PHB thin films were obtained by spin-coating of chloroform-polymer solutions on glass substrate. The films were extensively characterized by X-ray diffraction and AFM. In this work it has been shown that the local interaction of the polar groups of the polymer with the glass substrate reduces the chain mobility, precluding the crystallization within a tens of nanometers thick region close to the polymer-substrate interface. That makes possible to obtain stable amorphous PHB nanofilms at room temperature, opening a new insight into the technological applications of this polymer. Above this critical film thickness the polymer is able to crystallize, but the polymer chains tends to lie down parallel to the air-polymer interface. This crystal growth anisotropy is reduced with the increasing of the film thickness.