Decoupling of Dynamic and Thermal Glass Transition in Thin Films of a PVME/PS Blend

Abstract

The discussions on the nanoconfinement effect on the glass transition and glassy dynamics phenomena have yielded many open questions.Here, the thickness dependence of the thermal glass transition temperature T g therm of thin films of a PVME/PS blend is investigated by ellipsometry. Its thickness dependence was compared to that of the dynamic glass transition (measured by specific heat spectroscopy) and the deduced Vogel temperature (T 0 ). While T g therm and T 0 showed a monotonous increase, with decreasing film thickness, the dynamic glass transition temperature (T g dyn ) measured at a finite frequency showed a nonmonotonous dependence that peaks at 30 nm. This was discussed by assuming different cooperativity length scales at these temperatures, which have different sensitivities to composition and thickness. This nonmonotonous thickness dependence of T g dyn disappears for frequencies characteristic for T 0 . Further analysis of the fragility parameter showed a change in the glassy dynamics from strong to fragile, with decreasing film thickness.

Elastically Collective Nonlinear Langevin Equation Theory of Glass-Forming Liquids: Transient Localization, Thermodynamic Mapping, and Cooperativity

“…Since collective elastic effects involve a scale-free displacement field, there is no intrinsic length scale in the usual sense. However, a cooperativity length can be defined by asking a question recently explored in studies of thin film heterogeneous dynamics [43,44,45,46]. There, one can define a length scale as the distance from the surface where some pre-determined fraction of the bulk alpha relaxation time is recovered.…”

Energy dependent XPS measurements on thin films of a poly(vinyl methyl ether)/polystyrene blend concentration profile on a nanometer resolution to understand the behavior of nanofilms

“…This is further supported by the fact that for films with a thickness of 30 nm, T g dyn is close to that of pure PS films as discussed in references [31,32]. This could also be interpreted as a form of nanophase separation.…”

“…Madkour et al hypothesized that this behavior is a counterbalance effect of a PVME-rich surface layer at polymer/air interface and an adsorbed layer at the substrate. 32 It is interesting to note that for the thinnest film, T g dyn is close to that of the thickest film where the formulated concentration of 25 wt% / 75 wt% matters.…”

“…Interestingly, T g dyn shows mostly no thickness dependence for the homopolymers studied.29,30 Contrary, experiments on thin films of Poly(vinyl methyl ether) (PVME) / Polystyrene (PS) blends carried out by BDS and SHS showed a unique thickness dependence of T g dyn . [31][32][33][34] while T g dyn values for PS and PVME are independent on film thickness. 28,35,36 For instance, for the sample composition of 25 wt% PVME and 75 wt% PS, a complicated dependence of T g dyn on the film thickness have been found by SHS (see Figure 1).…”

A Model for Non-Arrhenius Ionic Conductivity

“…On the other hand, the opposite trend has been also reported. In Table 2, an example for the case of a poly (methyl ethyl ether)/polystyrene (PVME/PS) blend is shown [46]. According to Equations (12) and (13), the trend exhibited by a-polystyrene and polyimide copolymer PA66/6I suggest that the bond strength E0Z0 increases and the fluctuation ΔEΔZ decreases by reducing the size.…”