Small‐angle X‐ray scattering on latexes

Abstract

Small-angle X-ray scattering (SAXS) is a tool which allows the study of the structure and the interaction of polymer latexes with great accuracy. The low electron density of the polymers used for the synthesis of latex particles as e.g. polystyrene allows the matching of the contrast by adding sucrose to the serum. Thus, scattering intensities measured at different contrast, i.e., at different excess electron densities can be evaluated (contrast variation). This yields precise information on the radial electron density of the particles. In this article recent SAXS-investigations on latex particles are reviewed. It is demonstrated that core-shell latexes can be analyzed precisely by contrast variation. The same method can be applied to swollen latex particles to examine the polymer concentration near the boundary to the water phase. Here it is shown that the depletion of the polymer molecules near this boundary is very small which points to a minute wall-repulsion effect. Since the excess electron density of polystyrene latex particles in water is very small, the scattering from adsorbed layers of surfactants dominates the measured intensity in this particular system. Therefore the adsorption equilibrium of a given surfactant as well as the competitive adsorption of two different surfactants on a polystyrene latex can be assessed by SAXS.

Adsorption of Anions on the Surface of Charge-Free Latex Particles as Revealed by Turbidimetric Measurements

“…The synthetic procedure (24) leads to a thin surface layer of polyethylene oxide chains which provide the steric stabilization of the particles. Small-angle X-ray scattering is highly suitable to elucidate this point in detail (25,26): The excess electron density of the PS cores of the latex particles dispersed in water is quite small whereas the excess electron density of the groups constituting the surface of the particle is high. Therefore the SAXS intensity of the latex is mainly determined by the surface, the spatial extension of which can be in turn investigated by SAXS in great detail.…”

“…Figure 1 gives the resulting scattering intensity of the latex employed for the present study. The details of the measurements, the treatment of data, and the fit procedure have been described in detail recently (25,26,24). The inset displays the resulting radial electron density deriving from a fit of the SAXS intensities.…”

“…Conductometric titrations were performed using a conductivity meter LF537 (WTW). The radial structure of the selected latex was analyzed by SAXS using a SAXS-camera described elsewhere (25).…”

“…Therefore a careful study of the radial structure of the particles has been performed using small-angle X-ray scattering (SAXS). As shown in a number of previous publication (25,26), SAXS is highly suitable to study surface layers of latex particles. Together with a study of particle interaction by turbidimetry these data furnish a comprehensive set of data to elucidate ion enrichment on defined particles.…”

In-Situ Structural Characterization of Single-Walled Carbon Nanotubes in Dispersion

“…For a dispersion system of monodispersed particles with random orientation, the generalized differential scattering cross section given by Eq. (5a) can be simplified to (Ballauff et al, 1996;Pedersen, 1997;Peterlik & Fratzl, 2006):…”