A Small-Angle X-ray Scattering Study of the Interactions in Concentrated Silica Colloidal Dispersions (original) (raw)
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Hard-sphere colloidal silica dispersions. The structure factor determined with SANS
Langmuir, 1988
Small-angle neutron-scattering experiments were performed on the D11 instrument at Grenoble. The colloidal dispersions in cyclohexane studied contained silica particles sterically stabilized by odadecyl chains terminally g-rafted to the surface. From dilute dispersions the mean particle radius and the radius distribution were obtained. With these single-particle parameters the scattering behavior can be modeled with a hard-sphere interaction potential at all volume fractions up to 4 = 0.4-0.5. Polydispersity effects on the representation of the structure factor were explicitly taken into account. These results confrm and amplify previous results on the modeling of a silica dispersion as a hard-sphere supramolecular fluid.
Structural study of silica particle dispersions by ultra-small-angle x-ray scattering
Physical Review B, 1995
An ultra-small-angle x-ray-scattering study showed several orders of Bragg diffraction for an aqueous colloidal silica dispersion in a vertically held glass capillary, the first peak being at 150". The same profile was observed when the capillary was rotated around its axis by (60X m)' (where m is an integer). A different profile was found at (30+60X m)' with the first peak at 85". This showed that a bcc lattice 0 was maintained with the (110) plane parallel to the capillary wall and with a lattice constant =3000 A, dllo =2100 A, and dppo = 1500 A. The closest interParticle distance (2D, "p) was 2600 A while the aver-0 age distance from the overall concentration (2Do) was 2900 A, indicating the non-space-filling nature of the crystal.
Partial structure factors in colloidal silica mixtures determined with SANS contrast variation
Small-angle neutron scattering experiments at various contrasts were performed on concentrated mixtures of colloidal spheres differing in size. Both colloidal components consisted of fairly monodisperse silica cores coated with a layer of octadecyl chains. Cyclohexane was used as dispersing medium; variation of the contrast was achieved by using mixtures of 'H-cyclohexane and *H-cyclohexane. Scattered intensities were measured at three volume fractions up to 0.4, at equal partial volume fractions. The different contrast dependence of the scattering amplitudes of both colloids allowed us to calculate partial structure factors. This was done using a method which has not been reported previously. Describing the intraparticle structures with layered-sphere models, and using a decoupling approximation, three partials were obtained from a system of linear equations. The scattering curves at the various contrasts constitute a consistent data set, at all volume fractions. Although the separate components interact like hard spheres, the partial structure factors in the mixture reflect marked deviations from hard-sphere behavior. Their nature can be qualitatively explained with an attractive interaction between unequal particles. This is confirmed with simple model calculations.
Soft Matter, 2011
Using atomic force microscopy (AFM) and small angle X-ray scattering (SAXS), we show a full comparison between structuring of nanoparticles in confinement and in bulk in order to explain the effect of confinement on characteristic lengths and the scaling law of the characteristic lengths. Three different-sized particle suspensions are used to check the generalization and the correlation between the characteristic lengths and the system parameters, like particle diameter and Debye length. The two characteristic lengths obtained from AFM force curves, the oscillatory wavelength l, which is related to the average particle distance, and the decay length x, which measures how far particle correlates to obtain periodic oscillations, are in good agreement with the mean particle distance 2p/q max and the correlation length 2/Dq in bulk, respectively, obtained from the structure peaks of SAXS diagrams. Although confinement causes layering of nanoparticles parallel to the confining surfaces, the characteristic lengths in the direction perpendicular to the confining surfaces follow the bulk behavior. The wavelength scales as r À1/3 with the particle number density r irrespective of the particle size and the ionic strength and shows a pure volume effect. Upon comparing with literature results, the l ¼ r À1/3 scaling law can be applied more generally for charged particles, as long as the repulsive interaction is sufficiently long-ranged, than the previous expression of l ¼ 2(R + k À1 ), which only approaches the value of average particle distance under specific conditions. The decay length x is controlled both by the particle size and the ionic strength of the suspensions, and x ¼ R + k À1 is proposed in the paper. In addition, the interaction strength, the force amplitude and maximum scattering intensity, increases linearly with particle concentration. On the other hand, the Monte Carlo (MC) simulations and approximate hypernetted chain (HNC) closure calculation based on Derjaguin-Landau-Verwey-Overbeek (DLVO) potential are employed to study the characteristic lengths from the theoretical point of view. The experimental wavelengths are in good agreement with the theoretical counterparts and the experimental decay lengths show the same qualitative behavior as theoretical ones on the particle size and ionic strength.
Langmuir, 2005
Small-angle neutron scattering (SANS) was used to investigate the interparticle interactions in concentrated dispersions of colloidal silica stabilized either by steric or by electrostatic repulsive interactions. In 10 mM NaCl, an adsorbed PEO layer is required to prevent flocculation, and particles are stabilized by steric repulsions. The adsorbed layer was made invisible to neutrons by contrast matching with the aqueous continuous phase. Dispersions of the same particles at the same concentrations but in the absence of added salt and adsorbed PEO were also studied. In both cases, the SANS spectra of concentrated dispersions show a peak at low Q, which is due to interparticle interactions: a structure factor. The SANS data can be described rather well by a homogeneous spherical form factor and a structure factor based on the Hayter-Penfold/Yukawa potential model. The steric potential was compared to the electrostatic potential obtained by fitting the SANS data of the bare silica dispersions. The steric potential shows a greater dependence on the particle volume fraction, which we ascribe to the penetration and compression of the adsorbed PEO layer as the particles approach.
In Situ Characterization of Colloidal Spheres by Synchrotron Small-Angle X-ray Scattering
Langmuir, 1997
We have performed small-angle X-ray scattering with a synchrotron source on dilute suspensions of colloidal spheres of polystyrene latex, Stöber silica, and microemulsion-grown silica. Many interference fringes are observed of the monodisperse particles over a large range of scattering vectors and more than 5 orders of magnitude in intensity. We present a straightforward method to deduce the radii, the size polydispersity, and the interface thickness of the particles from a Porod plot of one and the same in situ measurement. The radii agree very well with static light-scattering data. The radii are larger than the electron microscopy data of dry spheres and smaller than the hydrodynamic radii from dynamic lightscattering data. The size polydispersities are smaller than those obtained by electron microscopy, which is well explained by the intrinsic random errors of electron microscopy. We find that nearly all the particles have a homogeneous internal density and a sharp interface with the suspending medium of less than 1 nm wide. In one case of a stepwise synthesized particle, we have discerned a dense core and a less-dense shell, without contrast matching with the suspending liquid. It is concluded that synchrotron small-angle X-ray scattering is a very powerful technique for the in situ study of colloidal systems.
The Journal of Chemical Physics, 1991
Small-angle neutron scattering experiments at various contrasts were performed on concentrated mixtures of colloidal spheres differing in size. Both colloidal components consisted of fairly monodisperse silica cores coated with a layer of octadecyl chains. Cyclohexane was used as dispersing medium; variation of the contrast was achieved by using mixtures of 'H-cyclohexane and *H-cyclohexane. Scattered intensities were measured at three volume fractions up to 0.4, at equal partial volume fractions. The different contrast dependence of the scattering amplitudes of both colloids allowed us to calculate partial structure factors. This was done using a method which has not been reported previously. Describing the intraparticle structures with layered-sphere models, and using a decoupling approximation, three partials were obtained from a system of linear equations. The scattering curves at the various contrasts constitute a consistent data set, at all volume fractions. Although the separate components interact like hard spheres, the partial structure factors in the mixture reflect marked deviations from hard-sphere behavior. Their nature can be qualitatively explained with an attractive interaction between unequal particles. This is confirmed with simple model calculations.
Ultra-Small-Angle X-ray Scattering Profile of Colloidal Silica Crystal of 4-fold Symmetry
J Am Chem Soc, 1995
Several orders of Bragg diffraction were observed by ultra-small-angle X-ray scattering (USAXS) for colloidal silica particles with the average radius being 560 8, and with narrow size distribution (standard deviation being 8%) in a salt-free aqueous dispersion in a capillary. Diffraction peaks were displayed at such small angles as 149 x n" with n being an integer. The same profile was observed when the capillary was rotated around its axis by (90 x m)" (m: integer). Furthermore, a different profile was found at (45 + 90 x m)" with the first peak at 109".
The internal structure of layered colloidal particles determined with SANS
Journal of Applied Crystallography, 1990
Small-angle neutron scattenng measurements at various contrasts were performed on dilute colloidal silica dispersions in order to resolve the internal structure of the particles The particles were prepared by outgrowth of a commercially available silica core, followed by an estenfication of the surface silanol groups with stearyl alcohol Vanation of the scattering contrast was achieved by using mixtures of 'H, 2 -and 2 H, 2 -cyclohexane as dispersmg medium The scattering data were interpreted as onginating from a polydisperse system of spherical three-layer particles Model parameters were optimized sequentially, applying an increasing number of constramts Good agreement between experimental and calculated scattenng curves is obtained, even at higher K values and low contrasts In comparison with other particles in the same size range, these sihca particles represent a very suitable model system for smallangle scattenng experiments at higher volume fractions