Dispersions, coarse

The butter fat is a coarse dispersion readily removable on standing or by a centrifuging operation. The casein will be present in the skimmed milk as colloidally dispersed micelles of diameter of the order of 10 cm, and is associated with calcium and phosphate ions. 

Sec. VI.) Dispersions containing larger dispersed phases, usually 10-50 pm in size, are referred to as coarse dispersions, which include most pharmaceutical suspensions and emulsions. 

The defined size ranges and limits are somewhat arbitrary since there are no specific boundaries between the categories. The transition of size ranges, either from molecular dispersions to colloids or from colloids to coarse dispersions, is very gradual. For example, an emulsion may exhibit colloidal properties, and yet the average droplet size may be larger than 1 pm. This is due to the fact that most disperse systems are heterogeneous with respect to their particle size [1-2]. 

Coarse dispersion >1.0 pm Particles visible by ordinary microscopy do not pass through normal filter paper or semipermeable membranes Pharmaceutical emulsions and suspensions... 

J Swarbrick. Coarse dispersions. In AR Gennaro, ed. Remington The Science and Practice of Pharmacy, 19th ed. Easton, Pennsylvania Mack Publishing Co., 1995, pp 278-291. 

As is known, if one blows air bubbles in pure water, no foam is formed. On the other hand, if a detergent or protein (amphiphile) is present in the system, adsorbed surfactant molecules at the interface produce foam or soap bubble. Foam can be characterized as a coarse dispersion of a gas in a liquid, where the gas is the major phase volume. The foam, or the lamina of liquid, will tend to contract due to its surface tension, and a low surface tension would thus be expected to be a necessary requirement for good foam-forming property. Furthermore, in order to be able to stabilize the lamina, it should be able to maintain slight differences of tension in its different regions. Therefore, it is also clear that a pure liquid, which has constant surface tension, cannot meet this requirement. The stability of such foams or bubbles has been related to monomolecular film structures and stability. For instance, foam stability has been shown to be related to surface elasticity or surface viscosity, qs, besides other interfacial forces. 

A turbine with a preferred gas setting in the range 0.5-1.15 mm is used to produce the emulsions. The mixture may be recycled a number of times through the turbine or a series of turbines. Alternatively, a coarse dispersion may be produced and subsequently homogenized in the turbine. Although the patents cover emulsion compositions of 13-50% sulfur, 16.5-39% is the preferred range. 

P-A. Paramonov et al, Ibid 1967(63/20), 156—65 CA 69, 4085d( 1968) (Since it was found that mixts of coarsely dispersed AN and TNT of high-d were not suitable when, charged mechanically in borehole because they could not ensure complete detonation,... 

P.A. Paramonov, Ibid 1967 (63/20), 213-17 CA 69, 4083b (1968) [Safety props of coarsely dispersed AN expis contg TNT NaCl were studied with.identical compn, but at different degrees of dispersion. They were tested in a methane-air medium (9.5% methane) by expln of freely suspended ehges of different wts. The relative increase of the coarser particles of the active component in the Ammonite mixt lead to increased resistance to firedamp. An increase in the NaCI content of the coarsely dispersed expl also increased resistance to firedamp]... 

The rubber particle size in the final product increases several fold if the prepolymerization is carried out in the presence of a dilute aqueous solution of an alkane sulfonate or polyvinyl alcohol in place of pure water. The addition of a surface-active agent converts the coarsely dispersed oil-water mixture—obtained as above in the presence of pure water—into an oil-in-water emulsion. In this case even prolonged stirring during prepolymerization does not decrease the rubber particle size appreciably in the final product. The stabilization of the droplets of the organic phase in water by the emulsifier obviously impedes or prevents agitation within the polymeric phase. Figure 1 shows the influence of these three prepolymerization methods (under otherwise equal reaction conditions) on the dispersion of rubber particles in polystyrene. 

A foam is a coarse dispersion of gas in liquid, and two extreme structural situations can be recognised. The first type (dilute foams) consist of nearly spherical bubbles separated by rather thick films of somewhat viscous liquid. The other type (concentrated foams) are mostly gas phase, and consist of polyhedral gas cells separated by thin liquid films (which may develop from more dilute foams as a result of... 

Gas-liquid reactions form an integral part of the production of many bulk and specialty chemicals, such as the dissolution of gases for oxidations, chlorin-ations, sulfonations, nitrations, and hydrogenations. When the gaseous reactant must be transferred to the liquid phase, mass transfer can become the rate-limiting step. In this case, the use of high-intensity mixers (motionless mixers or ejectors) can increase the reaction rate. Conversely, for slow reactions a coarse dispersion of gas, as produced by a bubble column, will suffice. Because a large variety of equipment is available (bubble columns, sieve trays, stirred tanks, motionless mixers, ejectors, loop reactors, etc.), a criterion for equipment selection can be established and is dictated by the required rate of mass transfer between the phases. 

Suspension (lat. to float) are coarsely dispersed system with particle sizes bigger than I (T m. 

A blend between two highly immiscible polymers, 20% PDMS in Nylon 6 (PA6) has a very thin interphase thickness of 2A, as shown on Table 11.1, and, as a result a coarse dispersed morphology of about 10pm. Similarly coarse morphology in obtained when PDMS is blended with PA 6 amine-functionalized at each chain end to form PA 6/diamine. 

Suspensions are coarse dispersions of finely divided solids in a liquid. The solid particles have a mean particle size greater than 0.1 pm in diameter. Pharmaceutical suspensions are administered orally, topically, and parenterally and should avoid the following problems sedimentation, caking, flocculation, and particle growth. Physicochemical principles in the solid/liquid interface will be discussed in this section as they pertain to the preparation of good pharmaceutical suspensions. 

Fig. 10. Dependence of the packing factor of highly-loaded coarse-dispersion composites on vibration time. Numbers on the curves correspond to numbers of composites in Table 2...

Particle Size in Emulsions When a solid drug is suspended in an emulsion, the liquid dosage form is known as a coarse dispersion. In addition, a colloidal dispersion has solid particles as small as 10nm-5pm and is considered a liquid between a true solution and a coarse dispersion [44],... 

Visual observations of film thinning in a coarsely dispersed foam from 2% Nekal solution have shown [78] that at first colourless thick films are formed. After 20 s the vertical films reach thickness of about 0.1 mm (in the thicker part about 0.8 mm) and after 5 min become black (thickness less than 15 nm). Horizontal films, however, thin much slower. 

A significant effect of pressure on the rate of foam destruction was not established for coarsely dispersed foams with NBF, formed by blowing air through a single capillary in a NaDoS solution (10 3 mol dm 3 containing 0.4 mol dm 3 NaCl). In these experiments the pressure drop in the Plateau borders changed from 103 to 4.5-104 Pa and the maximum... 

These expressions give only qualitative indication for the possible direction in which the structural parameters can be regulated. For example, it follows from them that the same expansion ratio can be achieved in a foam with fine bubbles and, respectively, thin borders and films as well as in a coarsely disperse foam with thick borders and films. 

In classical colloidal chemistry, solid foams were traditionally ass ed to low or coarse dispersion systems, i.e. to systems with minimal pore (cell) sizes of about 1 im or more and with a degree of dispersion (specific surface) of 10 - 10 cm". ... 

In colloid chemistry all kinds of foams, both liquid and solid, are classified as lower coarse-disperse systems, i.e. such in which the minimum pore diameter is not less than 1 mm. The grouping of plastic foams into coarse disperse systems has until recently, been justified, since the minimum size of the cells that could be observed did not exceed this value. However, microcells have been discovered in polymer foam structures, this requires a revision of the old concepts regarding the dispersity. The real minimum size of microcells is a few hundredth of a micron and their number is well above that of macrocells. These results support the conclusion that plastic foams belong to the group of finely dispersed or colloid systems... 

Coarse dispersions (sizes >0.1 p.m) represent the macroscopic haze and is formed out of coagulated proteins, yeasts, and bacteria. 

Suspensions Heterogeneous systems containing coarsely dispersed material that settles. A wide variety of pharmaceutical preparations have been used as suspensions, for example. White Lotion, Magma of Bismuth, and Compound Mixture of Opium and Glycyrrhiza (Brown Mixture). In addition, several official ointments are suspensions of solids in a semisolid base. A large number of suspensions are categorized as mixtures in the United States Pharmacopeia and the National Formulary ... 

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. 

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