ABSTRACT
Disorder in conjugated polymers is a general drawback that limits their use in organic electronics. We show that an archetypical conjugated polymer, MEH-PPV, enhances its local structural and electronic order upon addition of an electronic acceptor, trinitrofluorenone (TNF). First, acceptor addition in MEH-PPV results in a highly structured XRD pattern characteristic for semicrystalline conjugated polymers. Second, the surface roughness of the MEH-PPV films increases upon small acceptor addition, implying formation of crystalline nanodomains. Third, the low-frequency Raman features of the polymer are narrowed upon TNF addition and indicate decreased inhomogeneous broadening. Finally, the photoinduced absorption and surface photovoltage spectroscopy data show that photoexcited and dark polymer intragap electronic states assigned to deep defects disappear in the blend. We relate the enhanced order to formation of a charge-transfer complex between MEH-PPV and TNF in the electronic ground state. These findings may be of high importance to control structural properties as they demonstrate an approach to increasing the order of a conjugated polymer by using an acceptor additive.
ABSTRACT
The effects of sodium chloride on the composition and structure of polyelectrolyte gel-surfactant complexes (PSCs) formed by the sodium salt of acrylamide-2-methyl-1-propane-sulfonic acid-co-acrylamide gels and cetylpyridinium chloride have been studied. At a low ionic strength of the solution, the composition of all the complexes is close to stoichiometric by charge. In the presence of 0.3 M sodium chloride, the composition of the complexes formed by the gel with 99 mol % charged groups is close to stoichiometric, while for the gel with 33 mol % charged monomer units, a nonstoichiometric complex with a high excess of the surfactant is formed. Further decrease of the charge density up to 10 mol % leads to partial or complete dissociation of the PSCs. The study of PSCs by the method of small-angle X-ray scattering (SAXS) shows that the complexes formed by the gels with high and intermediate charge densities are highly ordered. The decrease of the charge density of the swollen networks at first leads to a change in symmetry of the ordered domains in the PSCs and then to their disordering. The formation of nonstoichiometric PSCs at a high enough concentration of salt is explained by the effect of fitting, when the packing of the surfactant and polymer components in the PSCs is improved due to the inclusion of extra surfactant molecules together with their counterions in the ordered domains.
