Mechanical spectroscopy of laser deposited polymers

Abstract

Pulsed laser deposition (PLD) at 248 nm in ultra high vacuum was used to produce thin poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA) films. The ablation and deposition mechanisms were found to be similar in both systems. Having the same backbone, these polymers differ in the size of their polar side groups leading to changes in their dynamics. Studies of the relaxation processes were performed using mechanical torsion and bending spectroscopy by means of a double-paddle oscillator (DPO) and an in-situ plasma plume excited reed (PPXR), respectively. A strong increase of the mechanical damping was observed during annealing of the polymer films well above the glass transition temperature T g, while in-situ X-ray measurements did not reveal any structural changes. For PEMA, the glass transition temperature T g=335 K and the main absorption maximum appear at lower temperatures compared to PMMA (T g=380 K), allowing one to measure the mechanical properties in a much wider range above T g.