Analysis of Polymer Latexes by Small-Angle X-Ray Scattering

Abstract

Small-angle X-ray scattering (SAXS) is a well-established tool of materials science and colloidal physics. It has been applied to a great number of polymeric and colloidal systems [1-5]. This method, however, has not often been applied to latexes. It is interesting to note on the other hand that the analysis of polystyrene latexes with narrow size distributions [6,7] by SAXS played an important role in the early history of this method. A number of early workers in the field of SAXS [8-13] had shown that the minima and maxima seen in the scattering curve of a polystyrene latex (see e.g. p. 54 of ref. [1]) are related to the form factor of a homogenous sphere. Small-angle neutron scattering (SANS) [14,], on the other hand, has been used quite often to analyze the radial structure [15-27] and the surface [28-30] of latex particles. In the case of SANS a high contrast between the particle and the medium or between the different constituents of the particle may be achieved through appropriate substitution of hydrogen atoms by deuterium atoms [14]. Moreover, a variable contrast between the latex particles and the surrounding medium (water) can be adjusted through mixtures of H₂O and D₂O [14]. This allows the detailed study of the radial structure and surface of the particles through contrast variation which had been earlier established as an investigative tool for polymeric systems [31-37], biological structures (see ref. [38,39] and further citations given there), and in general for colloidal systems [40,41]. In addition, very small scattering angles can be achieved by neutron spectrometer as, for instance, the D11 at the Institut Laue-Langevin [42]. Hence, the magnitude of the scattering vector q (q=(4π/λ)sin(θ/2); λ: wavelength of radiation, θ: scattering angle; [1–5]) can attain values much smaller than 0.lnm^-1 which is necessary for a meaningful analysis of many colloidal svstems.