Impact of Varying Binary Solvent Gradients on the Solubility Parameters of Poly(3‐hexylthiophene)

Abstract

Current methods for estimating the solubility parameters (SPs) of a solute, particularly conjugated polymers and organic semiconductor moieties, suffer from theoretical and computational deficiencies that have led to many questions and investigations that seek improvement in solubility parameter theory. This investigation focuses on the variation of SPs of a protype conjugated polymer, poly(3‐hexylthiophene), using (1) different set of solvents and binary solvent mixtures having a broad range of chemical characteristics, and (2) multiple computational methodologies, for example, functional solubility parameter and Hansen solubility parameter approaches. The results reveal that the choice of solvents and the fitting methodology impact the empirical SPs when using the binary gradient method. The validity of the observed SPs and the relative contributions of the dispersion, polar, and hydrogen‐bonding interactions are further rationalized using linear solvation energy relationship modeling of the solubility data.

Impact of regioregularity on the solubility parameters of poly(3‐hexylthiophene)

“…Referring to Table 1, the experimental polar (δ P ) and hydrogen-bonding (δ H ) HSP and FSP parameters are all markedly larger than the theoretical SPs calculated using the additive functional group contribution methods (GCMs) developed by van Krevelen and Hoyftzer, 20,38 wherein the GCM parameters, δ P ≈ δ H ≈ 0 are consistent with a non-polar molecule. 19 These GCM results are actually in agreement with more advanced computational methods. For example, in an earlier investigation of P3HT-solvent affinities we used density functional theory (DFT/B3LYP/TZVPD) to optimize the geometry of a model regioregular P3HT trimer, and subsequent statistical thermodynamics calculations with the COSMOtherm program revealed a σ-potential consistent with non-polar P3HT.…”

“…The observed relationships between δ P and δ H and regioregularity is particularly interesting because it is well‐established that the polar and hydrogen‐bonding SPs of P3HT are uncharacteristically large given the structural and chemical functionality of the polymer. Referring to Table 1, the experimental polar ( δ P ) and hydrogen‐bonding ( δ H ) HSP and FSP parameters are all markedly larger than the theoretical SPs calculated using the additive functional group contribution methods (GCMs) developed by van Krevelen and Hoyftzer, 20,38 wherein the GCM parameters, δ P ≈ δ H ≈ 0 are consistent with a non‐polar molecule 19 . These GCM results are actually in agreement with more advanced computational methods.…”

“…Table 1 shows the Hansen and FSPs, HSP and FSP, respectively, of P3HT available in the literature. [14][15][16][17][18][19][20][21] Clearly there are disparities in the SPs based on the computational method (FSP, HSP), and the number (N) and types of solvent systems, that is, pure solvents and binary solvent (gradient) mixtures, used to determine the SPs. In addition, Table 1 emphasizes the disparate molecular weight properties, M n and PDI, of the P3HT samples used in these studies.…”

“…In addition, Table 1 emphasizes the disparate molecular weight properties, M n and PDI, of the P3HT samples used in these studies. With respect to solvents, it is wellestablished that the SPs of P3HT solute can vary depending on (1) the set of solvents used for the solubility study, 19,22,23 and (2) the molecular mass of the P3HT. 23 Thus, variations in the experimental constraints, for example, different solvents, and differences in the physical properties of the P3HT samples preclude us from using this data to obtain a comprehensive picture of how the solubility behavior and SPs of P3HT are impacted by molecular weight and regioregularity.…”

“…Table 1 shows the Hansen and FSPs, HSP and FSP, respectively, of P3HT available in the literature 14–21 . Clearly there are disparities in the SPs based on the computational method (FSP, HSP), and the number ( N ) and types of solvent systems, that is, pure solvents and binary solvent (gradient) mixtures, used to determine the SPs.…”