Swelling of poly(3-alkylthiophene) films exposed to solvent vapors and humidity: Evaluation of solubility parameters

White light interferometry was used to determine the swelling of poly(3-alkylthiophene)s (P3ATs), with different head-to-tail regioregularity, exposed to different volatile compounds (VCs): humidity, cyclohexanone, tetrahydrofuran and chloroform. Film expansion increases always from regioregular R-P3DDT, R-P3HT to regiorandom P3BT, P3DDT. Regular solution approach was used to determine Flory–Huggins interaction parameter between P3ATs and VCs. Solubility parameters δP ∼ 16.9 ± 0.8, 15.3 ± 0.4, 13.1 ± 0.3, and 12.5 ± 0.2 MPa1/2 evaluated for P3DDT, P3BT, R-P3HT, and R-P3DDT, respectively, were confirmed by the values extrapolated from surface tension data. Evaluated δP values should allow an easier strategy for P3AT solution processing aimed at optimized film structure of P3AT polymers and their blends.