Study of a Commercial SiO₂ Sol and Gel By Small Angle X-Ray Scattering: Effect of Sample Thickness and Interpretation by Means of Smoluchowski Scheme

Abstract

Abstract--Ludox HS Sit 2 sols at high concentrations show a peak in small angle x-ray scattering (SAXS) reminiscent to a "structure." The appearance of such a peak was found to depend crucially on the thickness of the sample cell used for SAXS measurements. The thinner the cell used, the more prominent the peak. When the thickness was larger than 2 rnm, it was no longer observable. When sols were treated with activated charcoal powders (in order to remove a surfactant) the peak became less prominent.For the cases where clear features for structure were absent (thick sample regime), the Smoluchowski scheme was utilized to study the nature of sols. Namely, the distribution of the Smoluchowski species were estimated by numerically calculating the size distribution of particles directly from SAXS data. The distribution was found basically bimodal, and the main distribution peak, particularly for dilute sols (less than 5 wt%), was consistent with primary particles of Sit2. The second distribution peak was strongly dependent on the concentration of Sit2 particles. The observed trend was that the higher the concentration of Sit 2 particles, the more prominent the second distribution peak and the locus of the maximum tended to move toward a smaller value in diameter. This behavior of the second distribution peak of the Smoluchowski species is no doubt a manifestation of the interparticle correlation. The observation of such behavior may provide a convenient means to characterize sols with interparticle correlation. This method was also applied for characterizing gels formed when the pH values were altered.

Nanoparticle metrology standards based on the time-resolved fluorescence anisotropy of silica colloids

“…Nevertheless, notwithstanding these constraints, the interpretation of fluorescence anisotropy we have proposed for probes bound to nanoparticles has been validated for the initial stages of silica gelation. In this case it has been shown to be consistent with what is known about the growth of silica nanoparticles from a variety of other techniques [4][5][6][7][8][9] and indeed is already finding broader application such as in studying the surface modification of silica [20,21].…”

“…Methods used for nanoparticle metrology include small angle x-ray scattering (SAXS) [4,5], small angle neutron scattering (SANS) [6], transmission electron microscopy (TEM) [7], light scattering [8], spectroturbidimetric methods [9] and electrospray [10]. However, all of these have drawbacks including SAXS and SANS being expensive and complex, TEM not being in situ and light scattering being increasingly difficult below 10 nm radius, which is a size that includes many of the new nanoparticles such as quantum dots, fullerenes and carbon nanotubes.…”

Small-Angle X-ray Scattering Studies of Fe-Montmorillonite Deposits during Ultrafiltration in a Magnetic Field

“…Small-Angle and Ultra-Small-Angle X-ray Scattering. Scattering techniques can be used to probe the different length scales involved in these charged platelike particles and their structural arrangements. − SAXS and ultra-SAXS (USAXS) measurements were carried out at the High-Brilliance Beamline (ID2) at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France . SAXS measurements were performed using a pinhole camera with a two-dimensional (2-d) detector, and USAXS profiles were obtained by a Bonse-Hart camera with two crossed-analyzers.…”

Light Scattering Study on Sol-Gel Transformation of SiO2 Colloid at Extremely High Concentrations

“…Figure 2 (Xu et al 1996) shows the sol-gel diagram in the pH-SiO2 concentration field, valid from 2 weeks to at least 6 mo. On changing the pH value, the sample remained as a stable sol at first, and after some induction period of hours to days, depending on the conditions, the sample lost fluidity and turned into gel rather suddenly.…”