Molecular Mobility and Glass Transition of Thin Films of Poly(bisphenol A carbonate)

Abstract

Glass transition behavior of thin poly(bisphenol A carbonate) (PBAC) films capped between two aluminum (Al) layers is investigated by means of dielectric expansion dilatometry and dielectric relaxation spectroscopy accompanied by contact angle measurements. The thermal glass transition temperature is more or less independent of the film thickness down to 20 nm. For thickness below 20 nm, an increase of T g is observed. Meanwhile, an increase of the relaxation time at a fixed temperature is observed for the film with the thickness of 19 nm on the basis of a careful analysis of the temperature dependence of the relaxation rates. A more detailed analysis of the relaxation map reveals that the Vogel temperature increases and the fragility decreases systematically with decreasing film thickness. These properties are discussed in terms of the formation of a boundary layer with PBAC segments adsorbed onto the Al electrode due to the strong interaction between the Al and PBAC layers (2.51 mJ/m2), which results in a reduced molecular mobility with regard to bulk PBAC behavior. As the dielectric strength is proportional to the number of segments fluctuating on the time and length scale of the dynamic glass transition, it is used as a unique probe of the deviations from bulk behavior. The temperature dependence of the penetration depth of the interfacial interactions on the structural relaxation is further quantitatively determined. The dynamic length scale of the perturbations into the chain conformations responsible for the deviation from bulk behavior is estimated to be smaller than 9 nm.

Combining Flash DSC, DSC and broadband dielectric spectroscopy to determine fragility

“…The reliability of these investigations is demonstrated by comparing results obtained from two polymeric systems selected for their amorphous structure: polystyrene (PS), considered as a reference material because extensively studied by F-DSC, and poly(ethylene terephthalate)-glycol (PETg) which is much rarely studied by F-DSC techniques. In a second time, the temperature dependence of the cooling rate obtained by F-DSC and DSC combination has been compared to the temperature dependence of the relaxation times classically obtained from broadband dielectric spectroscopy, experiment considered as the reference concerning the fragility measurements [22][23][24][25][26][27][28][29][30].…”

Effect of Confinement Geometry on Out-of-Equilibrium Glassy Dynamics

“…Here we show how the interaction with the interface plays a dominant role in determining the direction and magnitude of T g deviations. Other studies point in the direction of reduced confinement effects once annealing well above T g for polymers exhibiting T g reduction [117,119,147,157,190]. However, in this case data are much more scarce and, therefore, we focus our attention on T g data.…”

“…Among them we recall Al-capped polycarbonate (PC) [189], poly(ethylene terephthalate) (PET) [116] and poly(L-lactice) [107]. This is seen in numerous polymers.…”

Blocked crystallization in capped ultrathin polymer films studied by molecular simulations

“…Besides, some other researchers reported that an attractive interaction between the polymer chains and substrate can lead to the reduction of chain mobility, thus precluding crystallization in the thin films . Napolitano and colleagues observed irreversible chain adsorption in ultrathin polymer films due to interfacial interaction . Jeong et al .…”