Isothermal Crystallization Kinetics and Time–Temperature–Transformation of the Conjugated Polymer: Poly(3-(2′-ethyl)hexylthiophene)

Abstract

Thermal annealing strongly impacts the nano- and microstructure of conjugated polymers. Despite the fundamental importance for the resulting optoelectronic behavior of this class of materials, the underlying crystallization processes have not received the same attention that is encountered in other disciplines of materials science. The question arises whether classical treatment of nucleation and growth phenomena is truly applicable to conjugated polymers? Here, the isothermal crystallization behavior of the conjugated polymer poly(3-(2′-ethyl)hexylthiophene) (P3EHT) is monitored with differential scanning calorimetry (DSC). Avrami analysis reveals growth- and nucleation-limited temperature regimes that are separated by the maximum rate of crystallization. The molecular weight of the polymer is found to strongly influence the absolute rate of crystallization at the same degree of undercooling relative to the melting temperature. A combination of optical microscopy and grazing-incidence wide-angle X-ray scattering (GIWAXS) confirms that the resulting nano- and microstructure strongly correlate with the selected isothermal annealing temperature. Hence, this work establishes that classical nucleation and growth theory can be applied to describe the solidification behavior of the semicrystalline conjugated polymer P3EHT.

Glass Transition Phenomenon for Conjugated Polymers

“…For example, sidechain branch position could greatly affect the melting point of the polythiophenes. P3EHT showed a melting point of approximately 80 °C, much lower than that of P3OT (190 °C). A related work by the Gomez group also pointed to a similar direction, showing that the dynamics of the sidechain at different distance to the polymer backbone is vastly different .…”

“…The backbone T g of P3ATs depends on the regioregularity, as depicted in Figure . Regioregular P3ATs have higher backbone T g compared to regiorandom P3ATs, due to the greater degree of crystallinity which leads to nanoconfinement of the amorphous domains and hence a reduction in the mobile amorphous fraction; while the sidechain T g is relatively insensitive to the regioregularity as suggested by Pankaj et al Beside the sidechain length, the structure of the sidechain also plays an important role, as listed in Table 2 , P3OT and P3EHT have same number of carbons in the sidechain; however, P3EHT shows a T g of 24 °C, while P3OT has a T g of −13 °C …”

Controlling Polymorphism in Pharmaceutical Compounds Using Solution Shearing

“…Commonly used in metal and polymer melt systems, a TTT diagram is used to describe the solid-state phase transformations that occur by changing the processing temperature. 47 The resulting phase composition and microstructure of materials is often embedded in the diagram, making it useful to for understanding the link between processing conditions and polymorphism or microstructural change. 47 While the mechanisms of transformation are well understood for a TTT (Figure 22), it is unclear what directs the nucleation and growth rates in the solution shearing system.…”

“…47 The resulting phase composition and microstructure of materials is often embedded in the diagram, making it useful to for understanding the link between processing conditions and polymorphism or microstructural change. 47 While the mechanisms of transformation are well understood for a TTT (Figure 22), it is unclear what directs the nucleation and growth rates in the solution shearing system. As a preliminary hypothesis, it is possible that the mechanism of growth is different in the thick films, formed under a slow blade speed, compared to the thinner films formed using a fast blade speed.…”

Conjugated polymer single crystals and nanowires

“…Many groups have used small molecules, carbon nanotubes, and nanowires as nucleating agents to improve the crystallization of conjugated polymers . Heterogeneous nucleation of P3ATs has also been observed during isothermal crystallization …”