Silica spheres viscosity

Fig. 38. Apparent viscosity of various dispersions of silica spheres (2a = 20 nm) in solutions of 1 wt% polyacrylamide (Mw = 2 x 103 kg/mol) in glycerin (Otsubo and Umeya, 1984).

Particulates of fly ash are very fine. Some of the silica in the ash is found in the form of small silica spheres, called cenospheres or extendospheres, which make ash a very flowable material. This property not only makes ash miscible in a CBPC slurry, but it reduces the viscosity of the slurry and makes the slurry smooth, easily pumpable, and pourable. This property is a great advantage with CBPC-based drilling cements (Chapter 15). 

FIGURE 12.32 Shear moduli and dynamic viscosities measured for silica spheres at = 0.46, a = 28 2nm, O + a = 76 2nm(Mellemaetal. [68]). The broken lines correspond to the infinite shear viscosities (de Kruif et al. [43]) and the solid curves to the frequency dependence predicted by the visco-elastic fluid model of Table 12.4 with the measured values of 170,171 , and Gi. Redrawn from Russel et al. [31]. Reprinted with the permission of Cambridge University Press. 

Figure 13.13. Comparison of the behavior predicted from Equation 13.35 with the data tabulated by de Kruif et al [43] for the viscosity of dispersions of sterically stabilized hard silica spheres in cyclohexane. There are no adjustable parameters in Equation 13.35. Relative viscosity denotes r (dispersion)/r (cyclohexane). Relative volume fraction denotes 0/0. Couette and parallel refer to measurements with a Couette rheometer and a parallel plate rheometer, respectively. Zero and infinite refer to the limits y —>0 and y- < >, respectively.

Another very typical surfactant for the formation of W/O microemulsions is AOT [sodium bis(2-ethylhexyl) sulfosuccinate], and such systems have been intensively studied. For instance, viscosity of the hard-sphere type has recently been reported for a W/O microemulsion made up from water, AOTand hydrocarbon, and the relative viscosity equals those of latex or silica spheres of corresponding volume fraction [59]. However, here the situation is somewhat more complicated, since at higher concentrations and higher temperatures attractive interactions lead to a reversible aggregation of the droplets that has to be taken into account [60]. This clustering process (which has also been evidenced via other methods such as dielectric permittivity measurements [61] and dynamic Kerr effect experiments [62] leads to an increase in the relative viscosity with rising temperature. 

Surprisingly, nitrate melts (at 333 K) penetrate into silica spheres (2.7 mm diameter, 210 m2g-l) more slowly than nitrate solutions of similar viscosity and surface tension at room... 

Figure 4.38 Relative viscosity versus volume fraction of particles for sterically stabilized suspensions of silica spheres (radius =110 nm) in cyclohexane. The data are for low and high strain rates, y. (From Ref. 61.)...

Winslow (1949) reported that silica gel in a low-viscosity oil showed this effect under an electric field of 3 kV/mm. The fluid can be sheared with a force proportional to the square of the electrical field. For example, a 25% by volume of hydrophobic colloidal silica spheres of 0.75 pm diameter in 4-methylcyclohexanol showed ER responses at 40-4,000 Hz, although dc fields are also viable. Dispersants are often added to the suspension in order to prevent the settling of the solids. 

Figure 17.19. Variation of the normalized low shear viscosity, with the hard-sphere volume fraction, 0hs- Samples from the microemulsion (data taken from ref. (22)) were measured in a capillary ( ) or in a cone and plate rheometer (A). Open symbols show the data obtained for different radii of coated silica spheres in oil, taken from ref. (23), reproduced by permission of society of Rheology. The continuous line shows the prediction of equation (17.17)...

Figure 10.5 Low shear viscosity of (a) (O) 56 and (o) 94 and (b) (o) 153 and (O) 230 nm diameter silica spheres in cyclohexane, with rj from tables in van der Werff and de Kruif(52), (c) 78 nm radius silica spheres in cyclohexane, r]r as tabulated by de Kruif, et al. 53), and (d) polymethylmethacrylate spheres in decalin, based on findings of Poon, etal. 54). Lines represent Eqs. 10.9 and 10.10. In (a) and (b), solid and dashed lines refer to the smaller and larger spheres.

Jones, et al. examined 50 nm silica spheres coated with covalently-bound stearyl alcohol dissolved in Shellsol T(55). Viscosities were determined with Ubbelohde viscometers and with three different cone and plate instruments. Sphere volume fractions were taken as high as 0.635, corresponding to T]r as large as 9.2 10 . Shear thinning was apparent at concentrations above 0.4. Systems with (p > 0.64 could not be taken into the low-shear limit in which 17 (/c) becomes independent from /c, so the low-shear rj remains indeterminate at these very large concentrations. 

Figure 10.7 Low-shear viscosity of 50 nm silica spheres in Shellsol T, as fitted to a stretched exponential and a power law, with rj taken from Jones, el al. 55).

Figure 10.8 Low-shear viscosity of weakly charged 288 nm silica spheres in decalin, with fits to stretched-exponential and power-law forms, using measurements reported by Marshall and Zukowski(56).

Lee, et al. measured viscosity as affected by shear rate for silica sphere suspensions, finding shear thinning at lower shear rates(57). In some but not all systems and volume fractions above 0.5, a reproducible abrupt transition to shear tbickening was found at elevated shear rates. The transition shear rate depended on concentration and temperature. In contrast, Jones, et al plot only a shear thinning region. A possible explanation for this difference is provided by the Peclet number Pe,... 

A. Imhof, A. van Blaaderen, G. Maret, J. Mellema, and J. K. G Dhont. A comparison between the long-time self-diffusion and low shear viscosity of concentrated dispersions of charged colloidal silica spheres. / Chem. Phys., 100(1994),2170-2181. 

A third system that is claimed to behave as a model hard sphere fluid is a dispersion of colloidal silica spheres sterically stabilized by stearyl chains g ted onto the surface and dispersed in cyclohexane ". Experimental studies of both the equilibrium thermodynamic and structural properties (osmotic compressibility and structure factor) as well as the dynamic properties (sedimentation, diffusion and viscosity) established that this system can indeed be described in very good approximation as a hard sphere colloidal dispersion (for a review of these experiments and their interpretation in terms of a hard sphere model see Ref. 4). De Kruif et al. 5 observed that in these lyophilic silica dispersions at volume fractions above 0.5 a transition to an ordered structure occurs. The transition from an initially glass like sediment to the iridescent (ordered) state appears only after weeks or months. 

Van der Werff and de Kruif (1989) examined the scaling of rheological properties of a hard-sphere silica dispersion (sterically stable monodisperse silica in cyclohexane) with particle size, volume fraction and shear rate. The shear-thinning behaviour was found to scale with the Peclet number Pe = 6nt]sa yl k-QT), or the ratio of shear time to structure-build-up time, where a is the particle radius, is the viscosity of the solution, y is the shear... 

Other studies of the viscosity of spheres in suspension have been made by Manley and Mason (215) and Happel (216,), and the rheology of silica suspensions (noncolloidal) has been described by Pivinskii (217). 

Figure 5.13 Relative viscosity of hard sphere silica particle suspensions (black...

Figure 5.15 Relative viscosity ( s/ i) at low shear rate of hard sphere silica suspensions (circles). Quemada s model (solid line) with = 0.631 Batchelor s model (dashed line) and Einstein s model (dotted line). (Data from Jones et al, 1991)...

Small amounts of inorganic fillers such as fumed silica, high surface area alumina, bentonites, glass spheres and ceramics are mixed with polyols such as propylene glycol to increase viscosity for printed electrodes. Proposed printed electrodes are carbon black, graphite, metallic or plated metaUic particles. 

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