Thin semiflexible polymer films are of great interest to organic electronics and other technologies. Theory and simulations predict that the alignment layer in semiflexible polymers scales with chain stiffness. However, the thickness of this aligned layer at the buried interface is challenging to characterize directly. Using Mueller matrix variable angle spectroscopic ellipsometry, we have modeled the optical response of regiorandom poly(3-hexylthiophene) P3HT in order to extract the aligned layer thickness. We find that by approximating the optical properties of the aligned layer as regioregular P3HT, the data can be effectively modeled. An aligned layer with thickness on the order of predictions in previous work is detected in regiorandom P3HT films greater than 150 nm while thinner films exhibit greater birefringence. The regiorandom P3HT films were all found to exhibit a degree of optical uniaxial anisotropy.
