Calorimetric Glass Transition of Single Polystyrene Ultrathin Films

Abstract

The calorimetric glass transition (T g) is measured for single polystyrene ultrathin films using a commercial rapid-scanning chip calorimeter as a function of cooling rate and film thickness. Films have been prepared in two ways: spin-cast films placed on a layer of inert oil or grease and films directly spin-cast on the back of the calorimetric chip. For the films on oil or on grease, the 160 nm thick films show results consistent with those of a bulk sample measured by conventional DSC. On the other hand, the 47 nm thick film on oil and 71 nm thick films both on oil and on grease show a T g depression which decreases with increasing cooling rate; the magnitude of the T g depression is similar to results reported in the literature for the most mobile substrate-supported films. For films directly spin-cast onto the sensor, a T g depression is not observed for 47 and 71 nm thick films but is observed for a 16 nm thick film. These results are also within the range of the data on supported films in the literature but show a smaller depression than films on oil or grease. The effect of annealing is also investigated. For thick films and those directly spin-cast onto the sensor, annealing at 160 °C has no influence on heat flow curves; hence, T g values remain unchanged. For the 47 and 71 nm thick films on either oil or grease, the depressed T gs revert to the bulk values over the course of a day at 160 °C. Atomic force microscope (AFM) images show that annealing results in dewetting of the films with hole growth and thickening of the film to 200 nm, the latter of which is presumed to be the reason that T gs revert to bulk values.

Structural recovery of a single polystyrene thin film using nanocalorimetry to extend the aging time and temperature range

“…Consequently the assumption that the curve T f 0 vs. log q mimics the temperature dependence of the equilibrium relaxation time results in a slight underestimation of the relaxation time at higher temperatures and a slight overestimation of the temperature dependence and fragility. Both the normalized activation energy and fragility are consistent with our prior work on this high molecular weight polystyrene, with values calculated directly from the data located between those by conventional DSC (Dh/R = 124 AE 0.4 kK, m = 144 AE 0.4) [25] and by Flash DSC (Dh/R = 93 AE 0.2 kK, m = 107 AE 0.2) [26]. We note that for works over a limited range of cooling rates, a linear relationship between log q and reciprocal temperature T g or T f 0 is often assumed [25,28,50,52,53].…”

“…5 along with our previous results for conventional DSC [25,26] and rapid-scanning chip calorimetry [26]. The cooling rate dependence of T f 0 for this study is based on results from four separate chips and samples.…”

“…This high molecular weight polystyrene is identical to that used in our earlier structural recovery studies [25,26]. Polystyrene thin films were deposited by spin coating polystyrene dissolved in toluene (HPLC-grade; Sigma-Aldrich) onto freshly cleaved 6.45-cm 2 (1-in 2 ) mica substrates.…”

Aging effect of a molecularly imprinted polymer on a quartz tuning fork sensor for detection of volatile organic compounds

“…For example, it has been demonstrated that under different temperatures, nanomaterials behave differently [38]. For instance, Gao et al [39] and Williams et al [40]. showed that for a single layer of polymer film, the thinner the film, the lower its glass transition temperature, T g .…”

Effects of high cooling rates on solidification for nucleated and non-nucleated semi-crystalline thermoplastics

“…Uthaipan et al [31] showed for EPDM/PP and EOC/PP that particles acting as nucleating agents can counteract the suppressed crystallization at undercooling. For amorphous polymers like PS [32] or PC [33] a shift of the glass transition temperature to a higher value with increasing cooling rate was reported.…”