In this study, the phase behavior, structure and properties of systems composed of the cationic, cellulose-based polycation JR 400 and the anionic surfactants sodium dodecylbenzenesulfonate (SDBS) or sodium dodecylethoxysulfate (SDES), mainly in the semidilute regime, were examined. This system shows the interesting feature of a very large viscosity increase by nearly 4 orders of magnitude as compared to the pure polymer solution already at very low concentrations of 1 wt%. By using rheology, dynamic light scattering (DLS), and small-angle neutron scattering (SANS), we are able to deduce systematic correlations between the molecular composition of the systems (characterized by the charge ratio Z=[+(polymer)]/[−(surfactant)]), their structural organization and the resulting macroscopic flow behavior. Mixtures in the semidilute regime with an excess of polycation charge form highly viscous network structures containing rodlike aggregates composed of surfactant and polyelectrolyte that are interconnected by the long JR 400 chains. Viscosity and storage modulus follow scaling laws as a function of surfactant concentration (η~c(s)(4); G(0)~c(s)(1.5)) and the very pronounced viscosity increase mainly arises from the strongly enhanced structural relaxation time of the systems. In contrast, mixtures with excess surfactant charges form solutions with viscosities even below those of the pure polymer solution. The combination of SANS, DLS, and rheology shows that the structural, dynamical, and rheological properties of these oppositely charged polyelectrolyte/surfactant systems can be controlled in a systematic fashion by appropriately choosing the systems composition.

While nanoemulsions (10-200 nm) are not thermodynamically stable systems they can exhibit quite long term stability. In this paper oil/surfactant mixtures, containing diethylhexyl carbonate/ phenoxyethanol/parabens as oil and polyglyceryl-4 laurate/dilauryl citrate as surfactant, form nanoemulsions simply by dilution with water, i.e. by means of the phase inversion concentration (PIC) method. In order to study this highly interesting phenomenon an investigation at constant oil-tosurfactant (O/S) ratio was done by means of viscosity, conductivity, and UV/Vis-transmittance measurements. This phase study as a function of the dilution by water shows that at an intermediate water content a two-phase system of bicontinuous structure is formed, which exhibits a very pronounced viscosity and conductivity maximum shortly before the homogeneous nanoemulsion phase is reached. In the same region SANS shows a high degree of ordering of this bicontinuous structure. SANS and cryo-TEM investigations of the nanoemulsion regime show an increasing average size with dilution and, more interestingly, the presence of two populations with different average particle sizes around 10-15 nm and 25-40 nm. The relative proportion of each population depends on the amount of added water, leading to an average growth of the particle size with increasing dilution.

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