Suspension properties

Applications. The high heat tolerance and good salt compatibiUty of welan gum indicate its potential for use as an additive in several aspects of oil and natural gas recovery. Welan also has suspension properties superior to xanthan gum, which is desirable in oil-field drilling operations and hydraulic fracturing projects. It is compatible with ethylene glycol, and a welan—ethylene glycol composition that forms a viscous material useful in the formulation of insulating materials has been described (244). 

Because the core of an aqueous micelle is extremely hydrophobic, it has the abiHty to solubiHze oil within it, as weU as to stabilize a dispersion. These solubilization and suspension properties of surfactants are the basis for the cleansing abiHty of soaps and other surfactants. Furthermore, the abiHty of surfactants to stabilize interfacial regions, particularly the air—water interface, is the basis for lathering, foaming, and sudsing. 

A more flexible option from an operational viewpoint is the implementation of process-oriented enhancements that intensify particle separation. This can be achieved by two different methods. In the first method, the suspension to be separated is pretreated to obtain a cake with minimal resistance. This involves the addition of filter aids, flocculants or electrolytes to the suspension. In the second method, the period during which suspensions are formed provides the opportunity to alter suspension properties or conditions that are more favorable to... 

Due to the wide variety of filter media, filter designs, suspension properties, conditions for separation and cost, selection of the optimum filter medium is complex. Filter media selection should be guided by the following rule a filter medium must incorporate a maximum size of pores while at the same time providing a sufficiently pure filtrate. Fulfilment of this rule invokes difficulties because the increase or decrease in pore size acts in opposite ways on the filtration rate and solids retention capacity. 

The physical characteristics should be considered (in combination as appropriate) in relation to the proposed dosage form and route of administration. Factors to be considered extend to solubility characteristics, crystal form and properties, moisture or solvent content, particle size and size distribution (which may affect bioavailability, content uniformity, suspension properties, stability, and preclinical or clinical acceptability), polymorphism, etc. 

Carico, R.D. "Suspension Properties of Polymer Fluids Used in Drilling, Workover, and Completion Operations," SPE paper 5870, 1976 SPE of AIME Annual California Regional Meeting, Long Beach, April 8-9. 

Aspnes DE, Heller A (1983) Photoelectrochemical hydrogen evolution and water- photolyzing semiconductor suspensions Properties of platinum group metal catalyst emiconductor contacts in air and in hydrogen. J Phys Chem 87 4919-4929... 

Aspnes, D.E. and Heller, A. 1982. Photoelectrochemical Hydrogen Evolution and Water-Photolyzing Semiconductor Suspensions Properties of Platinum Group Metal Catalyst-Semiconductor Contacts in Air and in Hydrogen. J. Phy s. Chem., 87, 4919-1929. 

Because of low solubility of the compound in pure water, for the oral administration a suspension in an aqueous solution of hydroxyethylcellulose (0.5 %) was used. The solid state physical parameters (particle size, surface area, amorphicity and crystal modification) and the suspension properties (agglomeration tendency, homogenicity and dissolved part of the drug) had to be investigated. For the intravenous administration, an aqueous solution containing saline, DMSO and PEG 400 was used as formulation. 

Monte Carlo techniques were first applied to colloidal dispersions by van Megen and Snook (1975). Included in their analysis was Brownian motion as well as van der Waals and double-layer forces, although hydrodynamic interactions were not incorporated in this first study. Order-disorder transitions, arising from the existence of these forces, were calculated. Approximate methods, such as first-order perturbation theory for the disordered state and the so-called cell model for the ordered state, were used to calculate the latter transition, exhibiting relatively good agreement with the exact Monte Carlo computations. Other quantities of interest, such as the radial distribution function and the excess pressure, were also calculated. This type of approach appears attractive for future studies of suspension properties. 

This generic formula permits averages to be calculated for any pertinent suspension property /. When time-independent external forces F(e) and torques N(e) act on each of the suspended particles, Eq. (7.14), together with the net force- and torque-free conditions characterizing the neutrally buoyant... 

Kaolin or china clay (RI 1.56) is hydrated aluminum silicates of very fine colloidal dimensions in the natural state. Clays are used in the paints because of their extremely good dispersibility in water-based systems, good suspension properties, and good brushability and opacity. However, they have poor weather resistance. 

Criteria considered so far in the selection of a suitable clrng form for MDI development include drug solubility and excipient and component compatibility. In addition to these parameters, suspension properties need to be carefully considered in the selection process. These are discussed in more detail later in this chapter in the section on the development of MDIs. 

A homogeneous particle packing can be obtained when the suspension flow units do not change on a time scale of that of the coating process. In industrial practice it is often also desirable that the suspension properties are stable on a longer time scale (shelf life) for economic reasons. This means that sedimentation and ageing cannot be permitted amd must accordingly be prevented. 

The dry thickness is directly related to the wet thickness and always depends on suspension properties such as volume fraction solids and colloidal stability. In this respect self-metered and pre-metered coating flows do not differ. The self-metered process is much more complex, because the wet thickness also depends on the suspension properties. 

In assessing commercially available alumina powders we find Alox F as a promising candidate for the preparation of a coating suspension. Properties of this powder as provided by the manufacturer are mean particle size 4 pm... 

Water-soluble cellulose derivatives themselves adsorb onto solid particles and may for instance affect the suspension properties of these insolubles. The mechanisms involved are quite complex and depend on the polymer concentration. At low concentrations macromolecules influence the electrophoretic mobility and the flocculation of the particles. At higher concentrations, surface coverage by the adsorbed polymer is sufficient to prevent particle-particle interaction and thus to stabilize the suspension sterically. As an example, the effect of NaCMC (among other polymers) on the zeta potential, flocculation and sedimentation properties of sulfadimidine has been investigated by Kellaway and Najib [115,116],... 

Fracture geometry and extension during treatment depend largely on the rheological characteristics of the clean viscous fluid and suspensions or slurries prepared with viscous carrier fluids. Particle settling and distribution in the fracture also are affected significantly by suspension properties. 

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