Application of Small‐Angle X‐Ray Scattering as a Tool for the Structural Analysis of Industrial Polymer Dispersions

Abstract

Small‐angle X‐ray scattering (SAXS) was applied for the structural analysis of an industrial polymer dispersion in water (synthetic latex). For the preparation of the spherical latex particles under investigation, butadiene, styrene, and acrylic acid were used as monomers in a seeded emulsion polymerization process. The product is widely being used as a film‐forming agent for coatings in the paper‐making industry. It is demonstrated that by measuring the SAXS curves at different contrasts the overall particle size, mass density, polydispersity, and degree of heterogeneity can be estimated with a good accuracy, even without the necessity of a detailed fitting procedure. In particular, one obtains information about the spatial distribution of the various monomer units within the particles. Five isoscattering points could be observed in the contrast variation measurements and the scattering curves at all contrasts could be modeled with a fully consistent set of fit parameters. It is thus safe to conclude that the contrast agent sucrose does not affect the particle structure. A quantitative fitting of the experimental data set revealed that a significant amount of the poly(acrylic acid) is preferentially located in a thin shell of ca. 2 nm thickness around the core of the particles, that is mainly formed by poly(styrene‐co‐butadiene). The obtained results are fully consistent with additional measurements of the particle mass density, of the hydrodynamic particle radius by dynamic light scattering, and of the particle surface charge by potentiometric titration. It is concluded that SAXS is a highly useful tool for characterizing the structure of industrial latexes.SAXS data of a BAYSTAL® latex measured at various contrasts, the weight fraction of sucrose in the dispersion medium is given in the legend.magnified imageSAXS data of a BAYSTAL® latex measured at various contrasts, the weight fraction of sucrose in the dispersion medium is given in the legend.

The application of distance distribution functions to structural analysis of core–shell particles

“…Two sets of water sucrose solutions have been prepared: one set for dilution of the as-synthesized suspension compensating for the water in the sample following synthesis and another set for background subtraction to remove the solvent background from the experimental SAXS patterns of the colloids. The mass density of the water sucrose solutions agreed with those reported previously (Bolze et al, 2003;Bubnik et al, 1995). The linear relation between the electron density of a sucrose solution ( m , defined in e Å…”

“…) and its mass density ( m , defined in g cm À3 ) (Bolze et al, 2003) has been used in this work to evaluate electron densities of sucrose solutions.…”

“…Amongst these objects a dominating position is occupied by coreshell particles with spherical-like symmetry represented, for example, by vesicles (Discher & Eisenberg, 2002), liposome (Baumgart et al, 2003), micelles (Hamley, 1998), latex particles (Bolze et al, 2003) and viruses (Lin et al, 1999). Two different approaches are usually used in structural characterization of the core-shell particles: microscopy (electron, scanning and atom-force) and scattering (dynamic light, neutron and X-ray).…”

“…Inhomogeneous particles with at least two regions of electron densities differing in their sign, with respect to the scattering medium, show typical features in the distance distribution (Glatter, 1979). In this work, a set of distance distribution functions calculated from the SAXS patterns of latex core-shell particles obtained by the contrast variation method (Bolze et al, 2003;Stuhrmann, 1982) have been analysed to demonstrate the effectiveness of p(r) functions in an interpretation of the inner structure of core-shell particles.…”

Modeling of Intermediate Structures and Chain Conformation in Silica–Latex Nanocomposites Observed by SANS During Annealing

“…A particularly interesting system is based on latex film formation. The process of formation of pure latex films has attracted considerable attention over the past two decades [36][37][38][39][40][41][42][43][44] . Latex beads are brought into contact by evaporation of the aqueous solvent above the minimal film formation temperature.…”