Anisotropic suspension

There are no equivalent studies of concentrated anisotropic suspensions. This is because of the tendency of anisotropic particles to form oriented ordered structures such as micro-bundles of fibers. Batchelor [45] has modeled the flow of concentrated suspensions of large parallel fibers. Very large elongational viscosities are predicted. This was extended to suspensions in non-Newtonian fluids by Goddard [46]. 

Quite specific effects in the flow of dispersions of long fibers are connected with particles orientation in the flow. Indeed, the state of fibers during the flow changes greatly as compared the initial state, so that the material in a steady-state flow is an anisotropic medium. Therefore the viscosity of such a suspension may become independent of a fiber s length [30], The most strong effects caused by a deformation of anisotropic particles should be expected in transient flows, in particular if the particles themselves are flexible and deformed in the flow. 

This is obvious for the simplest case of nondeformable anisotropic particles. Even if such particles do not change the form, i.e. they are rigid, a new in principle effect in comparison to spherical particles, is their turn upon the flow of dispersion. For suspensions of anisodiametrical particles we can introduce a new characteristic time parameter Dr-1, equal to an inverse value of the coefficient of rotational diffusion and, correspondingly, a dimensionless parameter C = yDr 1. The value of Dr is expressed via the ratio of semiaxes of ellipsoid to the viscosity of a dispersion medium. 

Today, lipophilicity can be determined in many systems that are classified by the characteristics of the nonaqueous phase. When the second phase is an organic solvent (e.g. n-octanol), the system is isotropic, when the second phase is a suspension (e.g. liposomes), it is anisotropic, and when the second phase is a stationary phase in liquid chromatography, it is an anisotropic chromatographic system [6]. Here, we discuss the main aspects of isotropic and anisotropic lipophilicity and their biological relevance the chromatographic approaches are investigated in the following chapter by Martel et al. 

Most of the results presented in this section, including Eqs. (4.15)—(4.17), are not valid when the equilibrium state of the fluid exhibits global orientational order, for example, a global director. However, they do apply to an isotropic suspension of locally anisotropic objects, such as vesicles or liposomes, which may exhibit a local director, provided that long-range orientational correlations do not extend over a significant fraction of the volume sampled in the experiment. 

The effect of surfactant on the dispersibility of Au nanoparticles depends on the sort of ionic type. When AOT was used instead of DOAC, the color of sols changed blue indicating the process of coagulation and the suspension was not stable. Within a few hours, the colloids fully precipitated. Figure 9-4.33 shows a TEM picture of this system sampled just after ultrasonic treatment to promote dispersion of sols. The particles in this picture are anisotropic and irregular in shape, and the size is larger than for the case of DOAC, as seen in the histogram. However, it is... 

The tris and bis complexes of acetylacetone (2,4-pentanedione) (167) with chromium(III) have been known for many years (168,169).739 The tris compound is generally prepared by the reaction of an aqueous suspension of anhydrous chromium(III) chloride with acetylacetone, in the presence of urea.740 Recently a novel, efficient synthesis of tris(acetylacetonato)chromium-(III) from Cr03 in acetylacetone has been reported.741 The crystal structure of the tris complex has been determined.744 A large anisotropic motion was observed for one of the chelate rings, attributed to thermal motion, rather than a slight disorder in the molecular packing. 

NUMERICAL AND EXPERIMENTAL STUDIES OF THE WATER AND IONIC MOBILITIES WITHIN SUSPENSIONS OF CHARGED ANISOTROPIC COLLOIDS... 

Mourchid, A., Delville, A., Lambard, J., Lecolier, E. and Levitz, P. (1995) Phase Diagram of Colloidal Dispersions of Anisotropic Charged Particles Equilibrium Properties, Structure, and Rheology of Laponite Suspensions. Langmuir 11, 1942-1950... 

Porion, P., Al-Mukhtar, M., Meyer, S., Faugere, A.M., van der Maarel, J.R.C. and Delville, A. (2001) Nematic Ordering of Suspensions of Charged Anisotropic Colloids Detected by 23Na Nuclear Magnetic Resonance. The Journal of Physical Chemistry B... 

Aqueous suspensions of cellulose microcrystalhtes obtained by acid hydrolysis of native cellulose fibers can also produce a cholesteric mesophase [ 194]. Sulfuric acid, usually employed for the hydrolysis, sulfates the surface of the micro crystallites and therefore they are actually negatively charged. Dong et al. performed some basic studies on the ordered-phase formation in colloidal suspensions of such charged rod-like cellulose crystallites (from cotton filter paper) to evaluate the effects of addition of electrolytes [195,196]. One of their findings was a decrease in the chiral nematic pitch P of the anisotropic phase, with an increase in concentration of the trace electrolyte (KC1, NaCl, or HC1 of < 2.5 mM) added. They assumed that the electric double layer on... 

Example. A tailings stream from the hot-water flotation process (oil sands) contains 27 % (mass) solids. Estimate the suspension viscosity. Light-scattering analysis indicates that the particles are finely divided and anisotropic with a 10 Tm major dimension and a 0.5 pm minor dimension. Using Eq. 

In addition, a tactoid containing n sheets in such a disordered state is separated from an adjacent tactoid containing n sheets by inter-tactoid pores. If two adjacent tactoids are tilted with respect to one another, very complicated architecture may exist within the suspension. The description of such architectures should be performed in terms of correlation functions relating the spaces occupied by solids or by voids. Such an analysis is difficult for anisotropic objects. 

In colloidal suspensions of anisotropic particles, the static structure factor plays a prominent role in particle size analysis. We have used transient electric birefringence (TEB) and electron microscopy, in addition to laser light scattering, to correlate our analysis of particle size distributions of bentonite suspensions. The complementary nature of TEB and photon correlation spectroscopy (PCS) in particle size analysis will be discussed. 

Figure 1. Schematic diagrams of TEB and LLS instrumentation. P, pinholes L, lenses B, polarizers C, cell Q, quarter wave plate PMT, photomultiplier tube HVG, high voltage generator MP, microprocessor TR, transient recorder CL, correlator CT, counter 6, scattering angle. For the TEB setup polarizers B-, B2 have polarization axis oriented at tt/4 with respect to the x-axis, as shown in (a). After the light beam passed through the cell with electric field in the x-direction containing a suspension of anisotropic particles and the quarter waveplate with its fast axis oriented at tt/4 with respect to the x-axis, the transmitted light beam is polarized in the direction of 71/4 + 6/2, as shown in (b). Analyzer B has polarization axis oriented at 3t/4 + a as shown in (c).

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