Random and alternating fluorene/carbazole (F/Cz) copolymers with various carbazole contents (20−50 mol %) have been designed and synthesized for use as the hole-transporting as well as light-emitting layer in blue light-emitting diodes (LEDs). DSC analysis has indicated the complete suppression of the crystallizability of these polymers by the introduction of 3,6-carbazole linkages into the polymer backbone, which also results in changes in their optical properties. The absorption maximum has been blue-shifted with an increase in the carbazole content due to the interruption in the main chain conjugation. Meanwhile, the photoluminescent properties have been influenced by the sequence distribution of the fluorene segments as well as the carbazole content. The emission maxima and vibronic features of the alternating copolymers have changed with carbazole content, reflecting the differences in the electronic structures of the repeat units. However, in the case of the random copolymers, the emission spectra remain almost unchanged and are similar to poly(9,9-dioctylfluorene) (PF), despite the fact that the carbazole content increases up to 33 mol %. This feature has been attributed to the existence of longer fluorene segments in the random copolymers, which would be expected to have lower energy gaps, and thus effectively collect excitons from other parts of the polymer backbone. Consequently, the light emitted from these energy traps is similar to that from PF. Electrochemical studies indicate that the introduction of carbazole units effectively raises the HOMO energy levels, thereby facilitating hole injection. Controlling the carbazole content between 20 and 33 mol % results in copolymers with stable and reversible p-doping and n-doping processes. A test for a LED device from P(F3- alt -Cz) indicates that the F/Cz copolymers could be a good candidate for blue light-emitting and hole-transporting materials.

The surface excess of sodium dodecyl sulfate (SDS) in aqueous solutions of SDS and the polymer poly(vinylpyrrolidone) (PVP) has been measured as a function of SDS and PVP concentrations using neutron reflection. Below the critical aggregation concentration (CAC) the adsorption of SDS is increased by the presence of PVP, indicating that the two components interact cooperatively at the surface. Between the CAC and the critical micelle concentration (CMC) of the surfactant there is a slight depletion of SDS from the surface. Comparison of coverages determined by neutron reflection with those from earlier radiotracer work indicates that, in the higher concentration range, PVP is bound to the surfactant layer, creating a region from which surfactant is depleted, which is further evidence for a strong polymer/surfactant interaction at the surface. Comparison of the effect of added PVP on the surface tension with the neutron reflection measurements indicates that, even below the CAC, the surfactant complexes to the polymer to some extent in the bulk solution. There are no measurable effects of the polymer on the thickness of the surfactant layer at any concentration. There is an indication that at the surface the surfactant is slightly displaced outward from water on addition of polymer, but accurate structural determination of the mixed layer proved too difficult to be certain of this result.

Neutron reflection and surface tension measurements have been used to show that the surface properties of sodium bis(2-ethylhexyl)sulfosuccinate (Aerosol-OT or AOT) at concentrations below the critical micelle concentration (cmc) are dominated by divalent ion impurities. Previous determinations of the area per molecule at the cmc using surface tension measurements and the Gibbs equation have given values of about 100 Å2 or higher. Neutron reflection gives a lower value of 78 ± 3 Å2. A similar value can be obtained from surface tension measurements only in the presence of species which remove divalent ions from the solution. This suggests that the lower value is much closer to the correct value and that surface tension measurements on AOT will usually give misleading values of the coverage.

Small-angle neutron scattering has been used to study the structure and composition of mixed ionic-nonionic surfactant micelles. A comparison between two different mixed surfactant systems, sodium dodecyl sulfate (SDS) and hexaethylene glycol monododecyl ether (C 12 EO 6 ) and hexadecyltrimethylammonium bromide (C 16 TAB) and C 12 EO 6 , both in 0.1 M NaCl, has been made. In the latter system, ideal mixing is observed, and in the former, departure from ideality, broadly consistent with regular solution theory, RST, is observed. The deviations from the predictions of RST are attributed to subtle changes in the packing of the two surfactants in the mixed micelles. For the SDS/C 12 EO 6 mixture, the micellar aggregation number is essentially constant with composition and concentration, whereas for the C 16 TAB/C 12 EO 6 mixture there is a marked micellar growth with increasing concentration and mole fraction of C 12 EO 6 in solution. The SANS results on structure and composition are compared with the results reported for other mixed surfactant systems and are discussed in the context of recent theoretical developments.