Small Angle X-Ray Scattering studies in polymer colloids

PERUZZO, P.J.; ANBINDER, P.S.; PLIVELIC, T.S.; AMALVY, J.I.

Campinas

Congreso; 19ª. RAU Reunión Anual de Usuarios LNLS; 2009

Laboratorio Nacional de Luz Sincrotrón

A synthetic polymer colloid (latex) is de¯ned as a dispersion of polymer particles in a °uid medium (like water). The particles are generally spherical, monodisperse with a size range of about 50 nm to 500 nm in diameter. Small-angle X-rayscattering is a tool which allows the study of the structure and the interaction of these polymer colloids. Previously, we have discussed SAXS results performed on latex in the dried state, as ¯lm or powder. In this work SAXS-investigations on two series of latex dispersions are discussed. The first series is composed of polystyrene latexes where the colloidal stability is enhanced via a steric stabilization mechanism by chemically grafting of reactive diblock copolymers, forming a core-shell morphology. The second series of latexes is composed of nanocomposite particles dispersed in aqueous medium and prepared from the in situ polymerization of methyl methacrylate in the presence of preformed nanosilica particles. SAXS measurements on samples were performed at the SAXS2 beam line at the LNLS (Campinas, Brazil) using a monochromatic beam of wavelength 1.608ºA and exposure time of 300 sec, and a sample detector distance of 728.32 mm. In the firt case, since the excess electron density of polystyrene latex particles in water is very small, the scattering from the layer of the polymeric stabilizers dominates the measured intensity. In the silica/poly(methyl methacrylate) latexes dispersions, the curves are compared with those obtained with the same particles but in the dried state after water evaporation. As expected the curves obtained in the dispersion state exhibit more oscillations allowing a more detailed analysis of the morphology. Porod`s plots have an asymptotic linear regime for all the samples indicating the presence of abrupt and well-de¯ned interface. The results in all case are discussed using information from dynamic light scattering and transmission electron microscopy.