Qualitative discrepancy between different measures of dynamics in thin polymer films⋆

Abstract

We have used ellipsometry to measure the initial stages of interface healing in bilayer polystyrene films. We also used ellipsometry to measure the glass transition temperature T(g) of the same or identically prepared samples. The results indicate that as the film thickness is decreased, the time constant for the interface healing process increases, while at the same time the measured glass transition temperature in the same samples decreases as the film thickness is decreased. This qualitative difference in the behavior indicates that it is not always possible to make inferences about one probe of polymer dynamics from measurements of another. We propose a reason for this discrepancy based on a previously discussed origin for reduction in the T(g) value of thin films.

Viscoelastic properties and residual stresses in polyhedral oligomeric silsesquioxane‐reinforced epoxy matrices

“…This observation is expected since different techniques weigh the distribution of relaxation times differently. [87][88][89] The increase of the glass transition temperature with POSS content in this study is similar but slightly smaller than that found in the literature, in which a 7.7 K (based on DSC measurement) increase was reported for an DGEBA epoxy system with 10 wt % addition of monofunctional POSS. 29 The glass transition temperature of epoxy/POSS nanocomposites is determined by several competing factors: (1) the POSS cages hinder the motion of the polymer chains giving rise to an increased T g , (2) the bulky POSS cages increase the free volume of the system resulting in a lowered T g , 38 (3) the rigidity of interlayer between the POSS and the polymer matrix can cause T g to increase or decrease, the latter of which was referred to as an internal plasticization effect, 32 and (4) the multifunctionality of the POSS has the effect of increasing the effective crosslink density (increasing functionality of the junctions) and this would be expected to increase the T g .…”

Calorimetric glass transition temperature and absolute heat capacity of polystyrene ultrathin films

“…was observed by Forrest et al 25 On the other hand, the application of 10,000 psi in a platen press at 170 8C for 5 h in vacuo resulted in the sample recovering very nearly to the bulk behavior, as shown in Figure 4. We also show in Figure 4 that this treatment results in no change in C p or T g when applied to a bulk (45-lm-thick) PS sample.…”

Dielectric and thermal properties of epoxy/boron nitride nanotube composites

“…The BNNTs' embedment effectively decreases T g . This indicates that the BNNTs interact with the epoxy molecules, inducing their higher mobility and/or a higher time constant for the interfacial healing processes [42][43][44][45]. These interactions can be explained in terms of π-stacking noncovalent inter actions, which in this case, occur between diglycidyl ether of bisphenol A and the BNNTs' atomic layers [46].…”