Small-angle neutron-scattering studies of silica sols in water at high temperatures

Abstract

The temperature dependence of the interparticle interactions in a silica sol have been investigated in the range 298-533 K by small-angle neutron scattering. By applying the rescaled mean spherical approximation (MSA), due to Hansen and Hayter, closed analytic solutions of the structure factor, S(Q), for a screened coulombic potential have been fitted to experimental scattering data to obtain the effective surface charge and potential of the silica particles. As the temperature is increased, marked reductions in the interaction potential are observed, which are partially restored on cooling. These effects are ascribed to the considerable changes in the dielectric properties and ionic dissociation of water that occur at these elevated temperatures.

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

“…larger than 2 ram. However, using a 0.5 mm thick cell, we reproduced the earlier data (Shuin 1977;Matsuoka et al 1988;Ramsay and Booth 1983;Penfold and Ramsay 1985;Bunce et al 1985) almost completely. Artifacts are possible, but our observations appeared to be real.…”

“…glass capillary suggested an ordered structure from a peak in a SAXS curve for higher SiO2 and lower electrolyte concentrations (Matsuoka et al 1988). SANS studies on Ludox HS using a 1 or 2 mm quartz cell also indicated similar behaviors (Ramsay and Booth 1983;Penfold and Ramsay 1985;Bunce and Ramsay 1985). Table 2 summarizes the loci of peaks of the above scattering data.…”

“…One approach is to regard sol as liquid-like. The structure factor S(K) calculated using a model in which the pair potential is approximated as a hard core with a soft tail was fitted to that observed (Ramsay and Booth 1983;Penfold and Ramsay 1985;Bunce and Ramsay 1985). A soft tail is to model the screened coulombic repulsion between charged particles.…”

“…In earlier studies on Ludox Sit 2 SO1S by SAXS (Shuin 1977;Matsuoka et al 1988) and SANS, (Ramsay and Booth 1983;Penfold and Ramsay 1985;Bunce et al 1985) broad peaks were observed in the scattering data from highly concentrated sols (about 30 to 40 wt%) with the sample cell, the thickness of which varied from 1 mm (Ramsay and Booth 1983;) to 6 mm (Shuin 1977). In contrast in our study, such peaks were not observed when the thickness of the sample cell was t Permanent address: Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, B.C., Canada V6T 1Z1.…”

“…Thus, 1 wt% is not dilute enough for Ludox HS SiO2 sols to be completely free from interparticle correlation. For the cases where I(K) exhibits a peak as our thin sample regime or in previous papers (Shuin 1977;Matsuoka et al 1988;Ramsay and Booth 1983;Penfold and Ramsay 1985;Bunce et al 1985), an approximate form of P(K) is all that is required to extract a reasonable form of S(K) for discussion. However, such structureless SAXS data, as shown in Figure 6, do need a very accurate form of P(K) in order for S(K) to be evaluated accurately, so that slight variations of S(K) from unity can be utilized for discussion.…”