Thermal Probe Surface Treatment of a Bulk Polymer: Does a Surface Layer with a Lower Glass Transition Than the Bulk Exist?

The surface of a bulk polystyrene has been scanned using a AFM equipped with a thermal probe at different temperatures. Scanning at room temperature reveals a real picture of the surface roughness, while scanning 40 and 20 K below the glass transition of the bulk PS results in a very flat smooth surface. Scans at the T g show a deformation pattern corresponding to a rubbery substance. Finally, scanning 10 K above the glass transition temperature shows a surface with intense “droplet” formation. It is concluded that a thin surface layer (a few nanometers) exists, which shows a significantly lower glass transition. This effect can be used to manufacture supersmooth surface areas.