Colloidal dispersions of octadecyl grafted silica spheres in toluene: A global analysis of small angle neutron scattering contrast variation and concentration dependence measurements

Abstract

In this paper we report measurements of the form factor and the structure factor of a sterically stabilized colloidal dispersion consisting of silica spheres coated with octadecane in toluene by small angle neutron scattering ͑SANS͒. The phase diagram of this system shows the liquid-liquid coexistence line and also a jamming transition at higher concentrations, where the jamming line intersects the coexistence line roughly at the critical point. We have performed SANS experiments at a temperature well above the transition temperature and at various volume fractions , spanning from the very dilute regime ͑ = 0.2% ͒ to the critical concentration ͑ =16%͒ and the highly viscous regime ͑ = 39.2% ͒. Except for the very dilute regime, we observe a structure factor S͑q͒ in all other cases. We fitted our data over the whole concentration regime using a global fitting routine with a core-shell model for the form factor P͑q͒, taking into account the structure factor, which we describe with the Robertus model for an adhesive polydisperse core-shell particle. At a volume fraction of = 5% a SANS contrast variation experiment has been performed. From that the product of the volume of the shell and the amount of solvent within the corona of our core-shell particle could be determined. At the most probable shell thickness of 2.3 nm a solvent content of about 50% within the corona was found. Moreover we could conclude that the core is not interpenetrated by solvent molecules. From the contrast variation experiment followed that the structure factor at zero average contrast exhibits a strong q dependence, which is an effect of an inhomogeneous particle in combination with a size distribution.

Anisotropic Pair Correlations and Structure Factors of Confined Hard-Sphere Fluids: An Experimental and Theoretical Study

“…At the temperature of the present study, the colloidal suspension acts like a hardsphere fluid, as has been shown in Ref. [24] for the present batch of the suspension. This also provides support for using hard-sphere interactions in the theoretical calculations.…”

“…and q k denoting the out-of-plane and in-plane components of the scattering vector, respectively. In order to facilitate the comparison between experiment and theory, we have determined the experimental SðqÞ within the monodisperse approximation, which is a reasonable approximation for the present colloidal suspension [24]. The agreement between experimental and theoretical data is striking.…”

“…The bulk density was n b ¼ 0:75 À3 , corresponding to a bulk particle volume fraction b ¼ 0:39. Details on the synthesis and characterization of the colloidal suspension can be found elsewhere [24].…”

Reduced colloidal repulsion imparted by adsorbed polymer of particle dimensions

“…We first consider the case with a structure factor S(q) = 1, namely, dilute solutions. The total scattering intensity of a monodisperse system I(q) is given by [30][31][32]49] …”

“…Using the EHS or HPY potential, particle interactions of bare or polymer-coated colloids have been systematically explored for a variety of colloidal dispersions [5,32,[39][40][41][42][43][44]. Another semi-empirical potential often employed for analyzing the structure factor of adhesive colloidal particles is the square-well (SW) potential [8,45,46] or the stickyhard-sphere (SHS) potential [47][48][49], which has stemmed from the Baxter's sticky potential [50] describing the van der Waals (vdW) attractions between spherical particles. The structure factor for the SW potential has also been derived using the Percus-Yevick closure [51].…”