Coarse suspensions, stability

Flocculation comes from the Latin word flocculate meaning loose and woolly. Flocculated systems result in rapid rate of settling because each individual unit is composed of many particles and is therefore larger. However, due to the loose packing of floes they are easily dispersible on shaking. Deflocculated systems on the other hand are made up of smaller particles whose settling rate is slower, but the settled particles tend to form an irreversible compact and are difficult to redisperse. This phenomenon is called caking. For coarse suspensions, a deflocculated suspension will have better uniformity of dose but poorer stability... 

Now as far as experimental evidence goes, the limit of stability of coarse suspensions is not very different from that of fine sols i.e. about 20—100 milHmol of a monovalent electrolyte and not a much lower value.as would be suggested by the above considerations. It is true that the retardation effects on the London force (c.f. p. 104) make th secondary minimum less pronounced, but it will not disappear completely and the effect of retardation will be only to shift the limit of the radius of the particles for which the secondary minimum determines the stability to higher values. 

But in the case of such coarse suspensions the difference h ctwecn stability and flocculation is unfortunately much less pronounced ti ian for smaller parddes. as rhe large particles sediment rather quickly on their own account, are easily redispersed by shaking, and, owing to the small number of particles per mi i of voiurtic, sh. /w a very long time of coagulation. 

In the food industry it has often been difficult to obtain true viscosity measurements (unithj.j) of complex fluid foods such as coarse fruit suspensions. These are usually non-Newtonian suspensions. Fruit concentrates are dispersions of solid particles (pulp) in aqueous media (serum). Their rheological properties are of interest in practical applications related to processing, storage stability, and sensory properties. Expensive rheometers are often not available in quality control and product development laboratories. However, viscosity is nonetheless an important quality factor of these products. 

Nitrocellulose, pulped and given a preliminary or sour boiling, may be used directly without poaching. Deteriorated smokeless powder, containing nitro derivatives of diphenylamine and acidic decomposition products, may be reduced to a coarse powder under water in a hammer mill, and may then be used. Whichever is used, the first necessity is to stabilize it by complete removal of the acid. For this purpose, the material in the presence of water (which may contain a little chalk in suspension or urea in solution) is introduced into a still where it is dissolved with agitation in ethyl acetate to form a heavy syrup or lacquer, and is treated with some substance which is adsorbed by nitrocellulose more readily than acid is adsorbed. It is a curious fact that nitrocellulose is dissolved or dispersed by ethyl acetate much more readily... 

Emulsions and suspensions are disperse systems that is, a liquid or solid phase is dispersed in an external liquid phase. While emulsions are sometimes formulated from oily drugs or nutrient oils their main function is to provide vehicles for drug delivery in which the drug is dissolved in the oil or water phase. Suspensions, on the other hand, are usually prepared from water-insoluble drugs for delivery orally or by injection, usually intramuscular injection. An increasing number of modern delivery systems are suspensions - of liposomes or of polymer or protein microspheres, nanospheres or dendrimers, hence the need to understand the formulation and stabilization of these systems. Pharmaceutical emulsions and suspensions are in the colloidal state, that is where the particles range from the nanometre size to visible (or coarse) dispersions of several micrometres. 

Suspension systems of sticky slurry and paste-like liquid explosives with solid particles, based on the dispersion of suspended solid particles, should belong to suspension or coarse multiphase systems in colloid chemistry. In these suspension systems, the main issue is its dynamic instability, because the density of the dispersed particles and the density of the dispersion medium are different (generally, the density particle is greater than that of the medium), settlement or floating can occur with the role of gravitational field to separate the system, resulting in unevenness in composition and density of liquid explosive. Stability is the ability to overcome the so-called sink-and-float separation of two-phase components, therefore, within a certain period of use, the composition and density of explosive and other physical parameters remained unchanged and its properties are stable and reliable. 

Thus, in order to render the stability theory completely determinate, we need to specify in an unequivocal form both the conservation equations governing macroscopic suspension flow and all the rheological equations of state. This is easily seen to be possible for coarse dispersions of small particles. For such dispersions, normal stresses in the dispersed phase may be approximately described in terms of the particulate pressure as explained in Section 4, and this pressure can be evaluated for uniform dispersion states with the help of Sections 7 and 8. As a result, particulate pressure appears to be a single-valued function of mean variables characterizing the uniform dispersion state under study and of the physical properties of its phases. This single-valued function involves neither unknown quantities nor arbitrary parameters. On the other hand, if the particle Reynolds number is small, all interphase interaction force constituents also can be expressed in an explicit consummate form with help from the theory in reference [24]. This expression for the fluid-particle interaction force recently has been employed as well in stability studies for flows of collisionless finely dispersed suspensions [15,60]. 

Uses Thickener, gellant, solubilizer for pharmaceutical oral and topical sol ns., toothpaste, gargles, mouthwash coemulsifier, consistency agent in creams, liq. emulsions stabilizer in pharmaceutical oral and topical suspensions solubilizer for actives and essential oils in pharmaceuticals and cosmetics Properties Wh. coarse waxy mictobeads sol. in water, ethanol (95%), IPA insol. in ether, paraffin, fatty oils m.w. 9840-14,600 pH 5.0-7.5 (2.5% aq ) 100% cone. Storage 2 yrs. shelf life when stored In unopened original containers R.T. Lutrol F micro 127 [BASF AG]... 

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