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| - Analysis of Surfactants Adsorbed onto the Surface of LatexParticles by Small-Angle X-ray Scattering
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| Abstract
| - A comprehensive study of the process of adsorption of a nonionic surfactant C18E112 onto poly(styrene)(PS) latex particles by small-angle X-ray scattering (SAXS) is presented. The PS latexes (particle radii 35and 71 nm) employed in this investigation bear no chemically bound surface charges. The analysis of theprocess of adsorption by SAXS demonstrates that the point of saturation of the surface may be determineddirectly from the scattering curves. Free micelles are formed beyond saturation, and no second layer ofthe surfactant is built up at higher concentrations of the surfactant. Any association of the micelles withthe covered latex particle can be ruled out as well. Moreover, an analysis of the radial structure of thesurface layer in terms the zeroth and the second moment of the electron density of the layers along theradial direction is given. Both moments can directly be obtained from the SAXS data. The zeroth momentof the excess electron density corroborates the finding that the surfactant is firmly adsorbed onto thesurface of the particles. The average extension of the adsorbed layer (2−4 nm) as express through thesecond moment increases with the amount of adsorbed surfactant. This points to a stretching of the chainsdue to their mutual interaction when the point of saturation of the surfaced is approached.
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