Figure 4: Time evolution of the glass-transition temperature of films of PS97 and PS160 annealed for different times at 423 K.
From: The lifetime of the deviations from bulk behaviour in polymers confined at the nanoscale
(a) The increase in Tg of residual films of PS97 prepared at different annealing times follows the same kinetics as the irreversible adsorption process: the solid lines are obtained by normalization of the traces of Δɛhigh(t) collected during isothermal experiments. At short annealing times (t<ton), Tg is 5 K lower than in bulk (dash-dotted line) and increases till saturating at TgBULK+7 K at t≫tads. (b) A similar correlation is observed for ultrathin films of different thickness and molecular weight: PS97, 18 nm (red hexagons), 35 nm (violet squares), 300 nm (black circles); PS160, 20 nm (pink triangles) and 44 nm (green diamonds). (c) The difference between the Tg of the films (same symbols as in a, b were used) and the bulk value, ΔTg, is plotted versus the thickness of the interfacial layer adsorbed in the same annealing conditions; straight lines are linear fits of the different data sets. Although for ultrathin films bulk Tg is recovered at t≫tads, for residual films of PS97 ΔTg=0 is achieved at much shorter times. Error bars take into account the width of the glass-transition temperature as determined by capacitive dilatometry in cooling.
