A wrinkling-based method for investigating glassy polymer film relaxation as a function of film thickness and temperature

Abstract

We investigate the relaxation dynamics of thin polymer films at temperatures below the bulk glass transition T by first compressing polystyrene films supported on a polydimethylsiloxane substrate to create wrinkling patterns and then observing the slow relaxation of the wrinkled films back to their final equilibrium flat state by small angle light scattering. As with recent relaxation measurements on thin glassy films reported by Fakhraai and co-workers, we find the relaxation time of our wrinkled films to be strongly dependent on film thickness below an onset thickness on the order of 100 nm. By varying the temperature between room temperature and T (≈100 °C), we find that the relaxation time follows an Arrhenius-type temperature dependence to a good approximation at all film thicknesses investigated, where both the activation energy and the relaxation time pre-factor depend appreciably on film thickness. The wrinkling relaxation curves tend to cross at a common temperature somewhat below T, indicating an entropy-enthalpy compensation relation between the activation free energy parameters. This compensation effect has also been observed recently in simulated supported polymer films in the high temperature Arrhenius relaxation regime rather than the glassy state. In addition, we find that the film stress relaxation function, as well as the height of the wrinkle ridges, follows a stretched exponential time dependence and the short-time effective Young's modulus derived from our modeling decreases sigmoidally with increasing temperature-both characteristic features of glassy materials. The relatively facile nature of the wrinkling-based measurements in comparison to other film relaxation measurements makes our method attractive for practical materials development, as well as fundamental studies of glass formation.

Heterogeneous Polymer Dynamics Explored Using Static 1H NMR Spectra

“…The activation energy (E a ) increases for networks with larger R, while the entropy of activation (ln(τ 0 )) decreases for larger R. This behavior may be related to differences in the free volume fraction of the BTT and TCDDA moieties and the relative contributions of each to the network free volume with changing R compositions. Similar trends in E a and τ 0 have been observed for the polymer relaxation in nano-patterned polymer films [ 50 ] and polymer thin films [ 51 ]. From the Arrhenius behavior of τ eff , a compensation or isokinetic temperature (T comp ) was determined ( Figure 11 b) to be ~333 K (60 °C), which is below the T g for all R compositions but falls near the cure temperature (25 °C).…”

Tuning the Relaxation of Imprinted Polymer Films with Polymer-Grafted Nanoparticles

“…In summary, the addition of PGNP to thin PMMA films leads to substantial stabilization of nanoimprinted patterns and provide a simple strategy to control high temperature nano-structural integrity in imprinted polymer films. The relaxation dynamics of the imprinted patterns show a clear EEC effect in the activation free energy parameters that govern the pattern relaxation process, just as in recent experiments on relaxation of wrinkled thin polymer films of variable thickness [9] . Our results suggest a common origin of EEC relaxation in imprinted thin film polymer nanocomposites.…”

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