Free volume behavior in spincast thin film of polystyrene by energy variable positron annihilation lifetime spectroscopy

Relaxation of Ultrathin Polystyrene Films Hyperswollen in Supercritical Carbon Dioxide

“…In these variable-temperature measurements, δ HT takes into account the fact that H ∞ increases with temperature due to the thermal expansion. For instance, H ∞ = 10.7 nm at 50°C and 11.0 nm at 100°C according to the thermal expansion coefficients provided by Ata et al 54 In the contrary to the relaxation at room temperature (δ RT ), the relaxation observed at high temperatures (δ HT ) is not linear with logarithmic time scale (Figure 6a) but can be rather well explained by the Kohlrausch−Williams−Watts (KWW) equation 61,62 dealing with relaxation dynamics of polymers. The solid curves correspond to fits using KWW equation, (2) where τ and λ are known as KWW parameters which represent the relaxation time constants and stretched exponent, respectively.…”

“…This discrepancy can be ascribed to the annealing effect and probably the nature of the substrates. Furthermore, using variable energy positron annihilation lifetime spectroscopy (EVPALS) Ata et al 70 reported that the free volume of thinner film (∼22 nm) is smaller than thicker one (∼1200 nm). As the density of thin film is correlated to its free volume, this clearly suggests that the thinner films should be denser than the thicker films under normal conditions of temperature and pressure.…”

Nanocharacterization of Lyotropic Liquid Crystalline Systems

“…PALS is a well -established technique used for investigating chain packing and nanostructure in polymer (Ata et al, 2009 ;Misheva et al, 2000 ) high -viscosity liquid (Jain, 1995 ) and recently lyotropic liquid crystals (Dong et al, 2009 ). It is used to provide an atomic -scale probe of the dimensions of free volume within materials, based on the lifetime of orthopositronimum (oPs) localized in inter -and intramolecular spaces.…”

On crystallization of bisphenol-A polycarbonate thin films upon annealing

“…However, free-volumes usually cannot be characterized accurately by some conventional experimental techniques. In recent years, positron annihilation spectroscopy (PAS) has been accepted as a new microanalytical probe for free-volumes in polymeric materials [13,14]. PAS is a powerful, nondestructive tool for the characterization of vacancy-type defects, surface and interface defects and free-volumes [15][16][17][18][19][20].…”