Probing relaxation of chain segments of polytert-butylacrylate film by force distance curve of atomic force microscopy

The force distance (F-D) curves of polytert-butyl acrylate (PtBuA) films have been studied by atomic force microscopy with various probing frequencies from 20 to 70 °C. The adhesion force is found to increase as the temperature increasing, which is corresponding to the glass-to-rubber transition of the polymer film. The F-D curve shows a typical shape in the case of about 2.5 nN applied force, but a break-free tail occurs in the case of about 24 nN applied force when the probing frequency is within an appropriate ranges, in which the polymer film transfers from the glass state to the glassy-rubbery state. We attribute the break-free tail to that the segments of PtBuA chains can be resonantly adhered to and released from the tip. Our observation indicates that the polymer segments adhered to the tip can be enhanced by their relaxation during the glassy-rubbery transition, and the average activation energy of the relaxation is estimated as about 2.1 eV.