Non-classical diffusion of PDMS confined in a surface forces apparatus

We present FRAP measurements inside a surface forces apparatus. Polydimethylsiloxane (PDMS), well above its glass transition, was confined into molecularly-thin films between atomically smooth mica sheets. Translational diffusion was measured using fluorescence recovery after photobleaching (FRAP) as the polymer film thickness was changed from tens of Rg to 3 Rg . The FRAP recovery curves of confined films are distinctly non-classical. Huge heterogeneity is suggested by stretched exponential behavior in which the power of time varies smoothly from $\beta $=1 (thick films) to $\beta $=0.3 (confined films) with a sharp transition between these limits.