Polymer layers can exhibit significantly improved performances if they possess a multicomponent phase-separated morphology. We present two approaches to control the dimensions of phase separation in thin polymer-blend layers; both rely on polymer nanospheres prepared by the miniemulsion process. In the first approach, heterophase solid layers are prepared from an aqueous dispersion containing nanoparticles of two polymers, whereas in the second approach, both polymers are already contained in each individual nanoparticle. In both cases, the upper limit for the dimension of phase separation is determined by the size of the individual nanoparticles, which can be adjusted down to a few tens of nanometres. We also show that the efficiencies of solar cells using two-component particles are comparable to those of devices prepared from solution at comparable illumination conditions, and that they are not affected by the choice of solvent used in the miniemulsion process.

A miniemulsion process has been used to create layers of conjugated semiconducting polymers from aqueous suspensions. Layers of particles with sizes ranging between 70 and 250 nm can be formed and annealing results in coalescing of the particles into large homogeneous domains (see Figure for a photoluminescence image of a Me‐LPPP layer).

We report on an experimental study of the self-organization and phase behavior of hairy-rod -conjugated branched side-chain polyfluorene, poly͓9,9-bis͑2-ethylhexyl͒-fluorene-2,7-diyl͔-i.e., poly͓2,7-͑9,9-bis͑2-ethylhexyl͒fluorene͔ ͑PF2/6͒-as a function of molecular weight ͑M n ͒. The results have been compared to those of phenomenological theory. Samples for which M n = 3 -147 kg/ mol were used. First, the stiffness of PF2 / 6, the assumption of the theory, has been probed by small-angle neutron scattering in solution. Thermogravimetry has been used to show that PF2 / 6 is thermally stable over the conditions studied. Second, the existence of nematic and hexagonal phases has been phenomenologically identified for lower and higher M n ͑LMW, M n Ͻ M n * and HMW, M n Ͼ M n * ͒ regimes, respectively, based on free-energy argument of nematic and hexagonal hairy rods and found to correspond to the experimental x-ray diffraction ͑XRD͒ results for PF2 / 6. By using the lattice parameters of PF2 / 6 as an experimental input, the nematic-hexagonal transition has been predicted in the vicinity of glassification temperature ͑T g ͒ of PF2 / 6. Then, by taking the orientation parts of the free energies into account the nematic-hexagonal transition has been calculated as a function of temperature and M n and a phase diagram has been formed. Below T g of 80°C only ͑frozen͒ nematic phase is observed for M n Ͻ M n * =10 4 g / mol and crystalline hexagonal phase for M n Ͼ M n * . The nematic-hexagonal transition upon heating is observed for the HMW regime depending weakly on M n , being at 140-165°C for M n Ͼ M n * . Third, the phase behavior and structure formation as a function of M n have been probed using powder and fiber XRD and differential scanning calorimetry and reasonable semiquantitative agreement with theory has been found for M n ജ 3 kg/ mol. Fourth, structural characteristics are widely discussed. The nematic phase of LMW materials has been observed to be denser than high-temperature nematic phase of HMW compounds. The hexagonal phase has been found to be paracrystalline in the ͑ab0͒ plane but a genuine crystal meridionally. We also find that all these materials including the shortest 10-mer possess the formerly observed rigid five-helix hairy-rod molecular structure.

Poly[9,9-di(ethylhexyl)fluorene] was studied by steady-state and time-resolved fluorescence techniques in solution in cyclohexane, methylcyclohexane, tetrahydrofuran, and decalin over the temperature range from 343 to 77 K. A decrease in temperature leads to a decrease in the inhomogeneous broadening of the emission band. Fluorescence decays were biexponential, consistent with a two-state model involving two different polymer conformers. Global analysis of the time profiles of luminescence collected at different emission wavelengths shows a long decay-time of 371.5±1.5 ps, which is temperature and solvent independent. The second shorter time (29±3 ps at 313 K and 100±3 ps at 233 K in methylcyclohexane) appears as a decay-time at the onset of the emission spectrum and as a risetime at longer wavelengths. Whilst the slow process was independent of temperature, the fast process showed Arrhenius type behavior, with an activation energy value of 0.10 eV found in both methylcyclohexane and decalin solutions. However, the risetime in the more viscous decalin was longer than that in methylcyclohexane. The observed behavior is interpreted in terms of fast conformational relaxation of the initially excited polymer, leading to a more planar conjugation segment.

We report on the influence of the molecular weight (M n) on the alignment and structure of poly(9,9-bis(ethylhexyl)fluorene-2,7-diyl) (PF2/6) in thin films on rubbed polyimide in the equilibrium. The degree of alignment has been studied using optical spectroscopy and compared to theoretical arguments. The structure of PF2/6 has been studied using grazing-incidence X-ray diffraction. PF2/6 realizes a threshold molecular weight M n* ) 10 4 g/mol separating a low Mn (LMW, Mn < Mn*) and a high Mn (HMW, Mn > Mn*) region. LMW materials show only the nematic (Nem) phase while HMW compounds show hexagonal (Hex) and Nem phases at low and high temperatures, respectively. LMW samples align equally well at any temperature above the glass transition, and the dichroic ratio, R, increases with M n. HMW material aligns well in the Nem regime, and R drops exponentially with Mn, which is in agreement with the theory. The orientational order is maximized near Mn*, and the orientational order parameter is >0.9. HMW samples, whether aligned or not, reveal two kinds of coexistent Hex crystallites distributed in the sample plane having one crystal axis a perpendicular or parallel to the surface. Local order within the triaxially aligned Hex phase surpasses that of the in-plane aligned Hex phase.