MOLECULAR-OPTICAL AND STRUCTURAL ANISOTROPY OF UNIAXIAL SINGLE-DOMAIN/POLYDOMAIN FILMS OF CONJUGATED POLYMER F8BT WITH AXIAL/PLANAR ORIENTATION OF MACROMOLECULES

Two types of uniaxial polymer films are used in practice. The first type is singledomain film on orienting substrate with axial orientation of macromolecules with
respect to the optical axis of the film n which is parallel to the substrate plane (type
ОА). The second type is polydomain film on isotropic substrate with in-plane orientation of macromolecules and the optical axis of the film n which is perpendicular to
the substrate plane (type ОP). The molecular-optical anisotropy of a film is defined
by the ensemble-averaged anisotropy δγ = γ|| – γ⊥ of the components γj of the polarizability of the monomer units of a polymer for the light-wave polarizations along
(j = ||) and across (j = ⊥) the optical axis n. The structural anisotropy of the film is
described by the orientation order parameters U of the dipole moments m of the
electronic (oscillatory) transitions in monomer units of macromolecule with respect
to axis n. For films of the same polymer, the values of Rδ(λ) = δγА/δγP and RU =
UA/UP characterize the closeness degree of the polydomain film to the ideal twodimensional polycrystal. In this work, the dependence Rδ(λ) on the light-wavelength
λ in the visible range and the order parameters UA(P) for the dipole moment of the
long-wavelength electronic transition in single-domain and polydomain films of the
conjugated polymer F8BT were studied. The values Rδ(λ) were determined from the
refractive indices nj(λ) of the films with the local-field tensor components fj(λ) = 1 +
Lj[nj
2
(λ) – 1]. The Lorentz-tensor components Lj were obtained using the dependences nj(λ). The values Rδ(λ) are in agreement with Rδ = –2 for two-dimensional
polycrystal consisted of the uniaxial crystallites. The parameters UA(P) were determined with the use of the background values nbj and maximal values kj
max of the
components of the complex refractive indices Nj(λ) = nj(λ) + ikj(λ) of the films in
the region of their long-wavelength electronic absorption band, taking into account
the background values fbj = 1 + Lj(nbj2 – 1). The experimental value RU differs from
RU = –2 for two-dimensional polycrystal. This difference reveals the sensitivity of
the parameter UP to the orientation disorder of the monomer units of macromolecules in interdomain regions of polydomain film