Accumulation of counterions and coions evaluated by cryogenic XPS as a new tool for describing the structure of electric double layer at the silica/water interface.

We introduce a new method of evaluating the structure of electric double layer (EDL) at the native solid/liquid interface using cryogenic X-ray photoelectron spectroscopy technique. This method is based on evaluating the atomic concentration ratio of counterions and co-ions of supporting electrolyte at the close-to-in situ state surface of colloid particles by the cryo-XPS and comparing it with analogous ratio predicted by EDL models. For silica colloids in aqueous KCl solutions at pH 6 to 8 it has been found that the latter ratio is higher than unity, as expected for the negatively charged surface of silica, but does not correspond with the prediction of the basic Gouy-Chapman EDL model for the ideal interface.

An identification of the soft polyelectrolyte gel-like layer on silica colloids using atomic force and electron microscopy.

A procedure is introduced for measuring the radius of spherical colloid particles from the curvature of upper parts of their central cross-sectional profiles obtained by atomic force microscopy (AFM). To minimize the possible compression and displacement of the spheres, AFM is operated in a mode rendering a constant ultralow pN force on the tip. The procedure allows us to evaluate the mean radius of nearly monodisperse submicrometer spheres of silica in their natively hydrated state in aqueous electrolyte solutions, irrespective of whether they are coagulated or not.

Influence of Corona Structure on Binding of an Ionic Surfactant in Oppositely Charged Amphiphilic Polyelectrolyte Micelles.

Interaction of polystyrene-block-poly(methacrylic acid) micelles (PS-PMAA) with cationic surfactant N-dodecylpyridinium chloride (DPCl) in alkaline aqueous solutions was studied by static and dynamic light scattering, SAXS, cryogenic transmission electron microscopy (cryo-TEM), isothermal titration calorimetry (ITC), and time-resolved fluorescence spectroscopy. ITC and fluorescence measurements show that there are two distinct regimes of surfactant binding in the micellar corona (depending on the DPCl content) caused by different interactions of DPCl with PMAA in the inner and outer parts of the corona. The compensation of the negative charge of the micellar corona by DPCl leads to the aggregation of PS-PMAA micelles, and the micelles form colloidal aggregates at a certain critical surfactant concentration.