Structure-property relationships in three-phase relaxor-ferroelectric terpolymers

Tuning the Relaxor–Ferroelectric Properties of Poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) Terpolymer Films by Means of Thermally Induced Micro- and Nanostructures

“…The shape of DHLs in terpolymers depends on several factors such as the maximum applied field, the measuring temperature, and the fractions of the ferroelectric and relaxor–ferroelectric phases in the respective sample, as seen in the difference between the DHLs measured at different temperatures on differently processed samples by Yang et al It should also be taken into account that the material undergoes significant changes during poling. Previously, it has been reported that the poling process can result in changes of the crystallinity and of the fractions of polar phases. − The nature of the termonomer has also been found to influence the hysteresis loops observed on the terpolymer. ,, It is obvious that the pinning effect of CFE is weaker when compared to that of CTFE due to its smaller size and higher dipole moment.…”

“…Strong effects of the proposed thermal treatments are also seen in the midtemperature transition ( T mid ). This transition usually shows up in the temperature range between 35 and 80 °C in DSC measurements on all VDF-based polymers; its origins were not clear until recently. ,, In the past, different explanations have been proposed to describe the T mid transition including (1) a second glass transition that takes place at a higher temperature than the conventional glass transition, (2) melting of secondary crystals formed as a result of aging, and (3) a conformational disorder (condis) relaxation process that is assumed to lead to flipping of the fluorine atoms in the TG + TG – chains from up to down or vice versa ( TG + TG – → G + TG – T ) . It is to be noted that the observation of a midtemperature process and the corresponding debate on its possible origin can be extended to several semicrystalline polymers including polyethylene, poly­( l -lactic acid), etc. − …”

“…As discussed in our recent publications, ,,, on the basis of the existing literature and additional experiments, a new hypothesis has been proposed in which multiple origins behind T mid are considered (only briefly explained here): When samples are heated from lower temperatures through their glass-transition temperature, the molecular chains in the amorphous regions (i.e., those found inside a more or less continuous amorphous phase) become flexible and can thus undergo molecular motions. However, amorphous chains at the amorphous–crystalline (a–c) interphase (such as tie, cilia molecules, and loops) that are constrained between crystallites remain frozen at this temperature. , As the sample temperature further increases, the molecules at the interface gain enough energy to unfreeze at their respective characteristic transition temperature which is commonly referred to as the second or upper glass-transition temperature ( T g,u ) .…”

“…20−22 The nature of the termonomer has also been found to influence the hysteresis loops observed on the terpolymer. 11, 18,23 It is obvious that the pinning effect of CFE is weaker when compared to that of CTFE due to its smaller size and higher dipole moment.…”

“…34 It is to be noted that the observation of a midtemperature process and the corresponding debate on its possible origin can be extended to several semicrystalline polymers 35 including polyethylene, poly(L-lactic acid), etc. 35−37 As discussed in our recent publications, 20,23,30,31 on the basis of the existing literature and additional experiments, a new hypothesis has been proposed in which multiple origins behind T mid are considered (only briefly explained here): When samples are heated from lower temperatures through their glasstransition temperature, the molecular chains in the amorphous regions (i.e., those found inside a more or less continuous amorphous phase) become flexible and can thus undergo molecular motions. However, amorphous chains at the amorphous−crystalline (a−c) interphase (such as tie, cilia molecules, and loops) that are constrained between crystallites remain frozen at this temperature.…”