Search

We investigate the structure and the osmotic pressure versus concentration of a colloidal crystal of charged bromopolystyrene particles of diameter 100 nm. In a concentration range between 2 and 12% volume fraction and in the presence of ion exchange resin which fixes a very low (micromolar) salt concentration, a colloidal crystal is obtained. The packing structure evidenced via Ultra-Small-Angel X-ray scattering (USAXS) are either fcc or fcc in equilibrium with bcc. A strong diffuse band before the first Bragg peak is observed. The Q-values ratio of this diffuse pre-peak to the first Bragg peak is 1.44. Osmotic pressures of these colloidal crystals are measured with different salt contents. Particle structural charge and diameter are known. Assuming screened electrostatic potential is the main repulsive interaction stabilising the system, all measurements can be rationalized using a simple electrostatic model. The melting of the fcc structure occurs with an average displacement from equilibrium position, deduced from the screened electrostatic potential, which is 10% larger than for molecular solids. This type of study of the colloidal crystal osmotic pressure versus distance (in the range 300 nm) is equivalent to an ultraprecise atomic force measurement, since it allows measurements of forces smaller than 10−12 N. [ABSTRACT FROM AUTHOR]

Current models of microemulsion microstructure are reviewed and their predictive power tested by comparison between their predictions and scattering from some typical concentrated ternary microemulsions. [ABSTRACT FROM AUTHOR]

Anomalous flow birefringent phases, sometimes designated as L3, have been identified in both the water-rich and the oil-rich parts of the phase diagram of the water(-NaCl)-dodecane-pentanol-SDS system. The presence of these phases appear to be associated with that of swollen lamellar phases. Conductivity and neutron-scattering results provide evidence that the structure of these phases consists of a highly connected, sponge-like, random bilayer-continuous surface. The surfactant surface separates, depending upon the system, into either two water-continuous domains or two oil-continuous domains. The data are consistent with a recent theoretical model. [ABSTRACT FROM AUTHOR]

We present further evidence in support of our Disordered Open Connected (DOC) model for microemulsion structure: small-angle X-ray scattering (SAXS) data for the systems didodecyl dimethyl ammonium bromide (DDAB)-octane-water and DDAB-dodecane-water. The models is a simple geometrical approximation to a random interface of constant mean curvature. Using only the composition of the sample and the desired curvature of the oil-water interface, we predict the SAXS spectrum, the position in the phase diagram of the conductivity anti-percolation, and the approximate boundary of the single-phase region. [ABSTRACT FROM AUTHOR]

The ternary phase diagram of the water/2-O LauroylSaccharose (LS)/didodecyl dimethyl ammonium bromide (DDAB) is determined versus temperature using an extension of the gradient method. Three phase equilibria regions are localized. The existence of these phase equilibria is due to a combination of electrostatic effects and steric effects. The high surface charge density of the double chain surfactant (DDAB) and the large polar volume of the single chain added surfactant (LS) induce coexisting repulsive mechanisms of steric and electrostatic origin which are directly measured using vapor pressure experiments. Critical demixtion of two lamellar phases formerly observed by temperature variation, can also be induced by adding LS. [ABSTRACT FROM AUTHOR]

The structure of aqueous solutions of the non-ionic amphiphile C12E8 is studied by small-angle x-ray and neutron scattering along the isothermal path across the single-phase region from 0% to 100% amphiphile volume fraction. Solution structuring is present even in the pure amphiphile, as shown by x-ray data. [ABSTRACT FROM AUTHOR]