Comparison of the Effective Radius of Sterically Stabilized Latex Particles Determined by Small-Angle X-ray Scattering and by Zero Shear Viscosity

Abstract

The influence of an adsorbed layer of a surfactant on the flow behavior of a latex is considered. The system studied consists of a poly(styrene) core latex without chemically bound charges (diameter: 146 nm) and a layer of poly(ethylene oxide) chains (length: 80 ethylene oxide units) affixed to the surface of the particles through adsorption of the surfactant Lutensol AT80 (C16 - 18EO80). Both the core latex as well as the latex covered by surfactant have been studied by small-angle X-ray scattering (SAXS). The hydrodynamic thickness of the layer was determined by rheology to be 11.7 nm whereas SAXS gives an extension of the layer of approximately 12 nm. The result demonstrates that realistic hydrodynamic radii of latex particles result from viscosimetric measurements. Relative viscosities measured at higher volume fractions compare favorable with a recent experimental master curve proposed for suspensions of hard spheres (Meeker, S. P.; Poon, W. C. K.; Pusey, P. N. Phys. Rev. E 1997, 55, 5718).

High-Frequency Viscosity and Shear Modulus of Sterically Stabilized Colloid Particles as Probed by Torsional Resonance Oscillation

“…A recent comparison of ⌬ thus obtained with structural data derived from small-angle X-ray scattering showed that both methods agree in good approximation (16). The value of ⌬ may therefore be used as a quantitative measure of the extension of the steric layer on the surface of the particles (cf.…”

“…The poly(styrene) core latex was prepared and purified as described recently (16). The analysis of the core latex showed that the radius a is 72.5 nm (number-average determined by transmission electron microscopy).…”

“…The latex has been prepared through adsorption of a nonionic surfactant C 18 EO 100 (Brij 700) onto poly(styrene) particles without permanent charges as described elsewhere (16). The core particles exhibit a very narrow size distribution so that polydispersity does not have a major impact on the resulting rheological data.…”

“…The method of preparation leads to particles with well-defined cores having a narrow size distribution coated by a layer of adjustable thickness. Recent experimental studies (11,16) have shown that such latexes present stable model systems for sterically stabilized colloid dispersions. Special attention has been paid to the effect of permanent or adsorbed charges which would lead to an additional electrostatic stabilization.…”

Modeling the Viscosity of Concentrated Nanoemulsions and Nanosuspensions

“…With the decrease in the droplet diameter, the relative viscosity increases sharply at any given volume fraction of oil nanodroplets. Figure 5 shows six sets of data for nanosuspensions [14,18,[53][54][55]. The type and size of nanoparticles vary from one set to another.…”