Enthalpy of fusion of poly(3-hexylthiophene) by differential scanning calorimetry

Abstract

The enthalpy of fusion for a perfect, infinite poly(3-hexylthiophene) (P3HT) crystal (DH 1 m ) must be known to evaluate the absolute crystallinity of P3HT. This value, however, is still ambiguous as different values have been reported using various experimental techniques. Here, we extrapolate the enthalpy of fusion for extended chain crystals of oligomeric P3HT to infinite molecular weight and obtain a value of DH 1 m 42.9 6 2 J/g employing differential scanning calorimetry with a correction based on grazing incidence small angle X-ray scattering data. Also, we define the onset of chain folding within P3HT crystallites at a chain length of 5 Kuhn segments. Knowledge of DH 1 m allows calculation of P3HT percent crystallinity in thin films for applications such as organic field effect transistors and solar cells. V C 2014 Wiley Periodicals, Inc. J. Polym.

Understanding the phase behavior from multiple-step isothermally crystallized poly(3-hexylthiophene)s

“…Multiple endothermic transitions in P3HT were observed by Remy et al [15] using specially prepared and almost monodispersed P3HT, such as T m ¼ 225 and 245 C was obtained during repeated DSC cycles using a specimen (DP66, M ¼ 1.1 Â 10 4 , PDI ¼ 1.11 and regioregularity > 98.9%). This confirmed that the multiple transition phenomenon is a universal characteristic related to P3HT structure and phase transition rather than difference in molecular weights.…”

“…They found that low molecular weight fraction consist of well-defined crystalline domains embedded in a disordered matrix [22]. Remy et al in 2014 reported the enthalpy of fusion from a perfect P3HT crystal with defined regioregularity may reach 42.9 ± 2 J/g [15]. These were substantially different from those reported by Zhao et al, in 1995 [14].…”

“…Phase behavior is commonly regarded as the key to control morphologies and relevant physical properties of the polymer. Phase transitions and structural features of P3HT have been investigated by means of differential scanning calorimetry [14,15]. Two crystal formation processes had been revealed, a fast process and a slow process [14].…”

Thermodynamic features of perfectly crystalline poly(3‐hexylthiophene) based on Flory's relation

“…Therefore, the absence of an accurate value for constrains the use of this common analytical technique to estimate the crystallinity. We had already a comprehensive review of the researches done for clarifying the heat of fusion of a perfect P3HT crystal and categorized the approaches used in the literature for obtaining the values of for P3HT in two classes: (a) The measurement of the melting temperature in diluent mixtures using the Flory equation and (b) investigating the dependence of the heat of fusion on crystallinity and crystal thickness . Applying the first method led to = 99 J/g, while the second approach yielded far lower values of ranging from 33 to 50 J/g for 100% crystalline, defect‐free P3HT.…”

Collapse Transition‐Assisted Crystallization in P3HT Solution

“…Recently, a renascent investigation into conjugated polymer solutions is underway with special interests on issues of order–disorder transitions, aggregations, gelations, and supramolecular self‐assemblies, which directly affect the microstructural morphologies of a condensed film through the so‐called “memory effect.” In the context of “nonclassical” crystallization theory, the crystallization involves multiple intermediate metastable amorphous phases . Understandings of the structures of these interphases and the transient disorder–order transitions are critically important for achieving satisfying microstructures and morphologies in the cast films, which is a long‐standing pursuit in solution processing of conjugated polymer films.…”