Crystallization in thin films of polymer glasses: The role of free surfaces, solid interfaces and their competition

Anisotropic material depletion in epitaxial polymer crystallization

“…We utilize an epitaxial polymer–substrate relationship to enforce edge-on crystallization in films which would otherwise adopt the flat-on orientation. 10–12 Our experiments, together with phase-field simulations, reveal that amorphous material depletion during edge-on epitaxial crystallization is highly anisotropic, in contrast to material depletion for flat-on crystal growth. We additionally demonstrate that epitaxial alignment is gradually lost as polymer crystallization occurs at higher crystallization temperatures.…”

Relaxations of Entropically Stressed Polymer Glasses

“…In this regard, it is noteworthy mentioning that spin-coated polymer films also show a trend of negative thermal expansion. ,− ,, We remark, however, that at present it is not clear whether films obtained via spin-coating shrink upon heating because of entropic or enthalpic effects or a combination of both. The reason behind the lack of consensus might be that the degree of nonequilibrium and energetic state of thin polymer layers prepared by spin-coating depend on a complex set of processing parameters (solvent quality, spinning rate, degree of adsorption, , substrate roughness, etc . ), often ignored while assessing the material behavior.…”

Length Scale of Molecular Motions Governing Glass Equilibration in Hyperquenched and Slow-Cooled Polystyrene

“…Local motions can considerably excite dense packing in a larger scale with the excess mobility transferred via the chain connectivity, 31,32 behaving as hierarchical facilitated dynamics. 11,12,33,34 The complex molecular dynamics of polymer glasses hint at complicated aging behaviors. Cangialosi et al 13−16 reported that the aging of polystyrene (PS) and polycarbonate (PC) below the T g − 10 °C were well-separated into two steps with decoupled time scales; 14 Androsch et al revealed the existence of a fast equilibration process of polyamide 11 at lowtemperature near T g − 80 °C.…”

“…Long-chain polymer glasses are characterized by multiple modes of localized molecular relaxation, including vibrational motions, − flipping, ,, rotation of side and end groups, ,, the rearrangement of side groups coupled with localized backbone motion, , etc. Local motions can considerably excite dense packing in a larger scale with the excess mobility transferred via the chain connectivity, , behaving as hierarchical facilitated dynamics. ,,, The complex molecular dynamics of polymer glasses hint at complicated aging behaviors. Cangialosi et al − reported that the aging of polystyrene (PS) and polycarbonate (PC) below the T g – 10 °C were well-separated into two steps with decoupled time scales; Androsch et al revealed the existence of a fast equilibration process of polyamide 11 at low-temperature near T g – 80 °C .…”

“…These aspects are captured by models as those based on Narayanaswamy’s material time concept, , specifically approaches based on the Tool–Narayanaswamy–Moynihan (TNM) and the Kovacs–Aklonis–Hutchinson–Ramos (KAHR) models. Approaches based on the free volume holes diffusion model , are also able to provide a description of physical aging, above all its acceleration in geometrically confined glasses. − Common features of the models aiming to describe physical aging is that they rely on the exclusive role of the main α-relaxation, and as a result, they are able to catch the time evolution in proximity of the glass transition temperature ( T g ) but fail to describe aging significantly below T g . − While these works indicate the presence of molecular processes associated with aging beyond the α-relaxation, the underlying mechanisms and the associated length scales for glasses equilibration are yet to be completely explored.…”