Silica suspensions

Values of are obtained partly by previous calibration using a series of standard light scatterers whose Rayleigh ratios have been precisely determined. Typical standards used in practice are poly(methyl methacrylate) blocks, colloidal silica suspensions, or tungsto-silicic acid, H4SiW 2O40-... 

The colloidal stability of silica Suspensions in the present work was assessed by sediment volumes and from the optical coagulation rate constant. In the first method, 50 mg of silica was dispersed in 5 cm3 polymer solution (concentration 10-2 g cm 3) in a narrow tube and the sediment height found at equilibrium. Coagulation rates of the same systems were found by plotting reciprocal optical densities (500nm, 1cm cell) against time. When unstable dispersions were handled, the coagulation was followed in... 

For SiC>2, we have only considered sources for silica suspensions which were non-porous, such as Ludox (39), pyrogenic silica (40), heat-treated BDH silica (22), or ground quartz (41). The data from these sources at 0.1M concentration has been collected in Figure 7. The data of the various researchers is quite consistent, in spite of the differences in origin of the suspensions, and the different electrolytes used. The slope of the points above pH 7 shows that the adsorption capacitance for cations is very large for both sodium and potassium ions, around 200 pF/cm2. Such a capacitance corresponds to a distance of 0.25.X, when using the dielectric constant of immobilized water molecules. The equilibrium constant for adsorption is low, however, since both KNa+ and Kk+ lie between 0.1 and 0.01 dms/mol. A possible interpretation of these results is as follows there is little specific attraction between SiC>2 and alkali cations,... 

Colloidal silica films spin-coated onto a glass substrate constitute another method to increase the surface area and therefore number of capture sequences which can be available for hybridization [43]. In this context, 0.3 p,m layers have been deposited from 20 wt % colloidal silica suspensions (particle size 16 to 65 nm). Heating to 350 °C for four hours is required to render the films sfable (fhrough parfial sinfering of fhe film with the underlying substrate). The particles pack randomly with no noticeable short- or long-range order. 

Silica particles synthesized in nonionic w/o microemulsions (e.g., poly-oxythylene alkyl phenyl ether/alkane/water) typically have a narrow size distribution with the average value between 25 and 75 nm [54,55]. Both water and surfactant are necessary components for the formation of stable silica suspensions in microemulsions. The amounts of each phase present in the micro emulsion system has an influence on the resulting size of the silica nanoparticle. The role of residual water (that is the water that is present in the interface between the silica particle and the surfactant) is considered important in providing stability to the silica nanoparticle in the oil... 

Composite samples are sectioned with a diamond saw and mounted in cold curing epoxy resin. Because of their porous nature, the composites are infiltrated under vacuum and subsequently cured under pressure in order to force the mounting resin into the pores. Mounted samples are ground flat on 240 grit silicon carbide paper, finely ground with a 9 pm oil-based diamond slurry and finally polished with a 1 pm diamond slurry and a 50 nm silica suspension. 

To elucidate some of these effects, PCS (photon correlations spectroscopy) measurements of the protein/A-300 systems were performed.4 The Oef(pH) graphs have a maximum close to pH(IEP) of the proteins (Figure 6). However, at pH far from pH(IEP) of the proteins, the PSDs of protein/A-300 are similar to those for pure silica suspensions, but Def is smaller pure silica due to decomposition of silica agglomerates and aggregates from the action of proteins. This effect is independent of protein type, since the interaction of protein molecules with silica particles can be stronger than between silica... 

To find the juroduct I A, we measured the scattering from a concentrated Ludo -- colloidal silica suspension and evaluated the integral Q in the equation—... 

It has been established that the pH needs to be above about 4 for reaction 9.14 to proceed. Thus, in the case of Fe(III), where nucleation already starts at pH around 2, the silica surface is not able to compete, and Fe(OH)3 particles are generated in solution. These particles do not subsequently react with the silica surface upon further increasing the pH, resulting eventually in a separate, rather than supported, iron (hydr)oxide phase. However, iron(III) can be deposited on Si02 by injecting a weakly acidic Fe(III) solution into a silica suspension, whose pH is kept above 5. 

A more common situation is the effect of adsorption on the stability of a suspension. This may be favourable (by modifying, for example, the surface charge of the particles, or by increasing the distance between particles) or unfavourable. Such an example of the latter effect was found with non-ionic surfactant Triton TX-100 and silica suspensions. It was found that the adsorption produced micelle-like aggregates which underwent flocculation by a bridging mechanism (Giordano-Palmino et al.,... 

Figure 4 shows an example of weighted and unweighted (u j = I) methods of cumulants regressions of PCS data for a Stober [68,69] silica suspension. This example employs a quadratic cumulant (QC) expansion given by... 

Figure 5 shows an example of NNLS and CONTIN analyses of PCS data for a Stober 68) silica suspension (Fig. 4). In this example, the NNLS and CONTIN algorithms of Brookhaven s light scattering software (70) were used.

FIGURE 15.3 The relationship between potential (open) and viscosity (filled) for silica suspensions as a function of suspension pH nanosize A90 vs. Geltech microspheres (G). Viscosity was determined at a shear rate of 26.4/sec. Particle volume fraction given in percent. 

Many researchers have assessed the effect of pulsatile flow on different membrane processes with wide range of feeds. One of the first studies was by Kennedy et al. [48] who showed that flux in the RO of sucrose solution could increase by 70% by pulsatile flow at 1 Hz. Gupta et al. [49] reported a 45% enhancement of flux in MF of raw apple juice with a pressure waveform provided by a fast piston return followed by a fast forward stroke at 1 Hz. Jaffrin [50], using hollow fiber filters, demonstrated a 45% enhancement in flux in plasma filtration. Using the collapsible-tube oscillation generator described above, Bertram et al. [47] demonstrated that pulsation resulted in a 60% increase in permeate flux in the filtration of silica suspensions. 

Effect of fihering a Aimed silica suspension through microsieves on the results of laser difhaction (a) and ultrasonic spectrosct y (b). 

Fig. 4. Laser diffraction results of disagglomeration processes after adding compact particles to a stabilized dispersed system (a) and after adding fumed silica suspension (b).

The agglomeration of the primary particles creates a secondary pore system which adds to the pore system of the primary particles. These agglomerated particles could be applied in preparative chromatography. The size of the agglomerates can be adjusted between 2 and 20 nm by changing various parameters such as flow rate of the silica suspension and the diameter of the jet nozzle. 

Silica suspension, prepared as follows to a 2-L measuring cylinder containing 100 mL DEPC-water, add 60 g Si02 and fill up to 500 mL with DEPC-water. Stir on a magnetic stirrer until all the silica is resuspended. Leave suspension overnight at room temperature, to allow the silica to sink to the bottom of the... 

Check silica suspension carefully if the silica is not entirely covered with water, discard tube and use a new one. Vortex silica suspension thoroughly (the suspension must be homogeneous), add 40 pL to each tube, and vortex vigorously. Vortex suspension between every two tubes to assure good homogeneity. 

A. P. Philipse, B.C. Bonekamp and H.J. Veringa, Colloidal filtration and (simultaneous) sedimentation of alumina and silica suspensions Influence of aggregates. /. Am. Ceram. Soc., 73 (1990) 2720-2727. 

T etradecyltrimethyl-ammonium bromide and sodium salicylate with silica suspension... 

Fig. 14 Normalized Dcoii/Bo of PDMS coated silica suspension with = 0.3 in a symmetric mixture of toluene and heptane (solid circles) along with hard sphere suspension (open squares) at similar volume fraction. The hydrodynamic interactions expressed in H(q) for the two systems (solid squares for the hard sphere suspension) are shown in the inset [101]. This system is crystallized by sedimentation as seen in the photograph...

Franks, G.V., Zeta potentials and yield stresses of silica suspensions in concentrated monovalent electrolytes Isoelectric point shift and additional attraction, 7. Colloid Intetf. Sci., 249,44, 2002. 

Duin, N.J., Effect of surface forces on shear thickening in silica suspensions. Diploma Thesis, University of Twente, 1999, cited after [1815]. 

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