Localized probe of dielectric response of polymer free surface near the glass transition*

Experimental study of length scales in glassy systems can give new insights into the glassy dynamics. Finite size effects are studied in a polymer (PVAc) utilizing UHV non-contact atomic force microscopy (NCAFM) methods. Localized dielectric susceptibility is probed using the electrostatic interaction of a metal-coated AFM tip with a thick polymer film on a metal substrate. The depth probed below the free surface of the polymer is as small as 10 nm. A lockin amplifier is utilized to measure response from the surface in the second harmonic to extract the Tan(delta) (C’’/C’) response over frequencies of 0.1 - 100 Hz. Preliminary results for the smallest probed depths show an increase in the frequency of the alpha relaxation peak in Tan(delta) as compared with macroscopic measurements. Results for various probed depths will be discussed.