Determination of Solvent–Polymer and Polymer–Polymer
Flory–Huggins Interaction Parameters for Poly(3-hexylthiophene)
via Solvent Vapor Swelling
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Abstract
We
report the use of solvent vapor swelling of ultrathin polymer
films to determine Flory–Huggins solvent–polymer and
polymer–polymer interaction parameters (χ<sub><i>i–j</i></sub>) for poly(3-hexylthiophene) (P3HT) and
polystyrene (PS) over a wide solvent composition range. From the calculated
interaction parameters, we constructed a polymer/polymer/solvent phase
diagram that was validated experimentally. χ<sub>tetrahydrofuran–P3HT</sub> (1.04 ± 0.04) and χ<sub>CHCl<sub>3</sub>–P3HT</sub> (0.99 ± 0.01) were determined through swelling of ultrathin
P3HT films. Similar experiments using PS films gave χ<sub>tetrahydrofuran–PS</sub> = 0.41 ± 0.02 and χ<sub>CHCl<sub>3</sub>–PS</sub> = 0.39 ± 0.01, consistent with literature values. As expected,
these χ<sub><i>i–j</i></sub> parameters indicated
that P3HT is less compatible than PS with either solvent. From δ<sub>PS</sub> (17.9 ± 0.2 MPa<sup>1/2</sup>) and δ<sub>P3HT</sub> (14.8 ± 0.2 MPa<sup>1/2</sup>), determined through regular
solution theory, we calculated χ<sub>PS–P3HT</sub> =
0.48 ± 0.06 at 23 °C. The resulting phase diagram was validated
by solution-based transmission measurements of PS/P3HT blends in <i>o</i>-xylene. Although we focused on PS/P3HT blends in this
work, this approach is easily adaptable to other polymer/polymer combinations
of interest
