Energy dissipation during stationary flow of suspensions of hydrophilic and hydrophobic glass spheres in organic liquids

Abstract

Suspensions of both hydrophilic and hydrophobic glass spheres in dioctylphthalate behave similarly to suspensions of hydrophilic glass spheres in glycerol + water mixtures: Newtonian behavior is shown up to a solid volume fraction (Cv) of 0.4; at larger Cv values, Bingham behavior is observed with a yield value steeply increasing at cv > 0.45. Suspensions of hydrophobic glass spheres in glycerol + water mixtures, on the other hand, already show deviations from Newtonian behavior at Cv < 0.1. The phenomena indicate absence of coagulation in dioctylphthalate. The number of collisions between the glass spheres in noncoagulating suspensions with 0.45 < Cv < 0.58 is calculated. That part of the energy dissipated per collision, which is independent of the mutual velocity of the colliding particles, cannot be accounted for by the attractive potential energy between the spheres as calculated by the Hamaker equation; in this respect the situation is analogous to that observed on floc formation in coagulating suspensions. It is suggested that the energy dissipation concerned is caused by the motion of spheres in the vicinity of a colliding pair, with the number of spheres entrained decreasing with increasing mutual velocity of the colliding spheres.

Viscoelastic properties of concentrated suspensions

“…In dioctylphthalate (DOP) as a medium (apolar), no difference in steady flow rheological behavior could be observed between suspensions of unsilanized glass beads (hydrophilic) on the one hand, and suspensions of silanized glass beads (hydrophobic) on the other (6). The relative viscosities are identical for suspensions ofhydrophilic and hydrophobic glass beads in DOP, and for suspensions of hydrophilic glass beads in glycerol, a polar system.…”

“…Two of the present authors, in a previous paper (6), suggested that sheet formation by particles during shear (1 1-13) is held responsible for the shear-thinning character. On calculating the energy dissipation per unit of volume and time in simple shear by means of = T*'~, [21 one arrives at the conclusion that it is composed of two parts, ~1 = /JPL*+ 2 [3] ~2 = z0*+.…”

“…Silanization of the surface of an inorganic solid appears to change profoundly the rheological properties of its dispersions in organic liquids (1)(2)(3)(4)(5)(6)(7)(8). The effect is related to the tendency of the solid particles to coagulate and thus depends on the polarity of the medium (2).…”

The rheological behaviour of Ca(OH)2 suspensions

“…Rheological measurements were performed in an Epprecht 15T-FC rotation viscometer (Contraves AG, Ztirich) with rotating inner cylinder (~: 1.50 cm) and stationary outer cylinder (inner ~: 1.90 cm); effective length 5.98 cm [8]. Rheological measurements were generally performed in suspensions with c~ = 0.25.…”

“…T h u s , f = 7 can be obtained, at q = 2, by f ' = 4, which can be obtained from (8) throug h 6 / a = 0.1 and ro/a = 2.02. These values appear to be reasonable.…”