Structure of polydispersed colloids characterised by light scattering and electron microscopy.

The dynamics of growth and aggregation of colloidal silver iodide particles was followed by the static light scattering method. The particles were treated as spheres and they were stable in size in the defined time interval. This approach enabled the use of the Zimm plots in order to determine the radii of gyration and the radii of spherical particles. Stable AgI colloids, either positively or negatively charged, showed the usual Zimm diagrams, while the diagrams were untypical when the stability of the colloids decreased. The untypical Zimm diagrams showed 'curves' with envelopes and 'curves' with minima in the unstable domain and in the domain where the most rapid nucleation occurs, respectively. Satisfactory agreement of particle sizes within the limits of accuracy, determined using static--and dynamic light scattering data and of the values obtained from the electron microscopic images was shown. Fitting the theoretical and experimental data, P(theta) functions showed that the particle shapes approach the theoretical model for spheres and thin discs. The colloid stability of polydispersed aggregates was also explained using the second virial coefficient, its negative sign implying interaction of particles in the solution, its positive value indicating formation of new particles from the supernatant solution. In addition, the colloid stability can be characterised by the mass fractal dimension. For positive stable colloids, Dm = 2.70 +/- 0.26, it can be related to the reaction controlled processes, whereas for negative stable colloids, Dm = 1.97 +/- 0.19, it was attributed to the diffusion controlled processes.

Formation of vesicles in diluted aqueous solutions of surfactant investigated by direct analysis of light scattering.

Formation of aggregates in the binary systems of double-tailed surfactant, sodium 4-(1-pentylheptyl)benzenesulfonate, and water in the dilute regime was supposed to occur within 5.0-8.5% of surfactant concentration. The size of particles was determined by light scattering. In addition, the samples were observed at room temperature using an Axiovert 35 Zeiss polarized light microscope operated with differential interference contrast optics. The observed aggregates could, in theory, belong a vesicle phase. All the histograms obtained by light scattering showed a bimodal distribution of particles. Weight factors including intensity, volume and number distribution indicate 97-100% of small aggregate sizes, since the peaks for the big sizes indicate only a small number of the aggregate population. Small aggregates have shown monodispersity with diameters of the aqueous core amounting to 38.94 and 54.94 nm relating to the surfactant concentration of 6.0 and 8.0%, respectively. Hydrodynamic radii determined by the Cumulant method, by the inverse Laplace transformation, and using a plot 1/tau vs. q2, showed values within the usual precision limits.

Lyotropic Liquid Crystalline Phases from Symmetric Double-Tailed Surfactants: Sodium 1'-(6)-Undecylbenzenesulfonate, 1'-(7)-Tridecylbenzenesulfonate, and 1'-(8)- Pentadecylbenzenesulfonate in Water.

Phase diagrams of binary symmetric double-tailed alkylbenzenesulfonate surfactant/water systems, as well as the structure of the phases, were determined using crossed polars, polarized light microscopy, 2H NMR spectroscopy, Nomarski differential interference contrast optics, and cryo-transmission electron microscopy. The isotropic phase, the lamellar phase, and a high-viscosity solution representing an intermediate between the isotropic phase and the mesophase, which refers to the beginning of the formation of vesicles, were found. As may be expected, the isotropic phases at higher concentrations are formed mostly at higher temperatures. Isotropic regions are followed by regions characterized as the isotropic solutions containing vesicles; the optically isotropic phase contains a lamellar dispersion of vesicles in solution. The viscosity of these phases is found to be high near the borderline of the two-phase regions. At the same concentrations two-phase regions were found to contain the isotropic + lamellar phases at the higher temperature and the isotropic + crystalline phase at the lower temperature. Molecular-mechanical and semiempirical quantum-mechanical calculation searches for the global minimum in the conformational space of alkylbenzenesulfonate ions were conducted to examine the influence of monomer molecular structure on the micellar shape. Copyright 1998 Academic Press.