Dispersions In Non-aqueous Media Research Articles

Ni–Cu bimetallic colloids prepared in nonaqueous solvents

Colloidal dispersions in nonaqueous media were obtained by simultaneous evaporation of Ni and Cu. The metals were cocondensed at 77 K in an organic matrix of 2-methoxyethanol, 2-propanol or acetone. The metallic dispersions were characterized by transmission electron microscopy, electron diffraction and UV–vis spectroscopy. The stability at room temperature was also measured. The stability of the Ni–Cu bimetallic dispersions is less than that of the Ni and Cu dispersions alone. The presence of more than one phase was observed. It is interesting to note that Ni/Cu ratio does not change the stability of the bimetallic dispersions dramatically. The polarity of the solvent should play a very important role in stabilizing the metal particles by solvatation effects. Transmission electron microscopy studies show the size control effect of Cu with small colloidal size in the bimetal. The electron diffraction studies reveal the presence of amorphous bimetallic particles and particles with crystallinity show typical particles formed for more than one phase (NiO, CuO, Cu, Ni and Cu–Ni). Cu and Ni, for example, are amorphous and crystalline particles, respectively. Differential scanning calorimetry and X-ray spectroscopy characterized the bimetallic solids of Ni–Cu/2-methoxyethanol obtained by evaporation of solvent. The differential scanning calorimetry studies of the solids show transition characteristics of crystalline growth; no glass transitions were observed. The X-ray diffractograms show that the crystallites are too small (less than 100 A), giving rise to low intensity and wide peaks.

Electrostatic stabilization in non-aqueous media

This paper discusses electrostatic stabilization of dispersions in non-aqueous media. It begins with the theory of repulsion, with particular attention to the roles of the dielectric constant and ionic strength of the liquid medium. Results for flat plates and spheres are compared. Methods are reviewed to measure the dielectric and electric parameters in non-aqueous media, in conjunction with procedures to determine the mechanical properties of electrostatically stabilized, concentrated suspensions. From theoretical considerations it appears that the extent of the electrostatic stabilization in non-aqueous media is extremely sensitive to the dielectric constant ϵ of the liquid, affecting stability in particular through the degree of dissociation of the stabilizing electrolyte. It is essential that, besides the presence of charge on the particles, there also are certain levels of ions in the solution to ensure a sufficient force of repulsion. It is expedient to distinguish three regimes of ϵ: (a) ϵ ⩾ 11, the (semi-)polar range, where systems can be charge-stabilized more or less as in aqueous systems, (b) the low-polar regime (5 ⩽ ϵ ⩽ 11), where electrostatic stabilization is possible provided some dissociated electrolyte is present and (c) the apolar range (ϵ⩽ 5), where screening is exclusively determined by the polarization of the solvent, and where electrostatic stabilization may be more problematic. Concentrated dispersions of solids in liquid nonionic carriers with dodecyl-benzene sulphonic acid (HDBS) as the stabilizer arc good models for the ‘low polar’ category, as detailed experimental data illustrate. In such media HDBS creates a ζ-potential, and enhances the dielectric constant and the ionic strength of the continuous phase. Especially when attraction between suspended salt particles in liquid nonionics is weak, electrostatic stabilization is easily achieved. This is particularly noticed in the rheology of the concentrated suspensions of some salts.

A light scattering study of concentrated dispersions in nonaqueous media

Interparticle interactions between colloidal poly(methylmethacrylate) particles stabilised by poly(12-hydroxystearic acid) in non-aqueous media have been investigated using time-average light scattering. The problem of multiple scattering was avoided by using a binary mixture of solvents such that the colloidal particles were optically matched. This enabled the static structure factor to be measured and from the small scattering vector expansion the osmotic pressure to be determined. The softness of the pairwise interaction potential has been exposed using the Chandler-Weeks-Anderson perturbation theory. However, it is concluded that dispersions of the type studied can be reasonably well approximated by a hard sphere fluid model.

Preparation of sterically stabilized silica dispersions in nonaqueous media

Preparation of sterically stabilized silica dispersions in nonaqueous media

Stability of dispersions in non-aqueous media. Part 8.—Theoretical analysis of heterocoagulation

The potential energy of charged colloidal particles in media of low dielectric constant has been derived by application of Maxwell's equations for the potential energy of charged conducting spheres. In this treatment the presence of an electric double layer is ignored. Data computed using the Maxwell expressions are compared with those obtained from the simple Coulombic law for repulsion between point charge. The differences are particularly significant for small particle separations. Serious errors are introduced by the use of Coulomb's law for particles interacting at constant potential, but for the constant charge case are significantly less although usually > 5 %.

Rheological studies on dispersions of uniform colloidal spheres: II. Dispersions in nonaqueous media

The study of aqueous dispersions of uniform colloidal spheres (I in this series) was extended to nonaqueous dispersions. These were prepared from aqueous crosslinked polystyrene latexes by two-stage solvent exchange dialysis, with methanol as intermediate solvent. Non-Newtonian relative viscosities η r were measured in benzyl alcohol and m-cresol at volume fractions φ up to 0.50, for particle diameters from 0.15 to 0.43 μ. A single rheological equation η r = f( φ, τ r ) was found to apply to nonaqueous dispersions in both media, and to aqueous dispersions the interparticle coulombic and van der Waals' forces of which are negligible. Here τ r = τa 3 kT is a reduced shear stress, in which r is the actual shear stress, a the particle radius, k Boltzmann's constant, and T the absolute temperature. The experimentally observed functional form of f was well fitted by Krieger and Dougherty's (1) modification of the Williamson equation, using their expression for the dependence on concentration of the high-and low-shear limiting viscosities.

The stability of colloidal carbon dispersions in nonaqueous media

Suspensions of carbon black in toluene, m-xylene, nitrobenzene, and aniline have been investigated. Rigorous desiccation of materials generally gave unstable suspensions; this was not the case where strong interactions between the particles and dispersion medium were possible. The addition of water to dry systems gave suspensions with varying degrees of stability; oxidation products of the suspension medium also had a marked effect on stability.

Principles of the stability of lyophobic colloidal dispersions in non-aqueous media

Principles of the stability of lyophobic colloidal dispersions in non-aqueous media