Dispersants, in aerosols

Rudinger, G. and Chang, A. (1964). Analysis of Nonsteady Two-Phase Flow. Phys. Fluids, 7,1747. Soo, S. L. (1960). Effect of Transport Process on Attenuation and Dispersion in Aerosols. J. Acoustical Society of America, 32,943. 

Any material that will burn in air in solid form may explode if it is dispersed in aerosol form. Explosions of foods, metals, pharmaceuticals, grain products, polymers, and other organic materials all have occurred in the past. Since oxidation is an exothermic reaction, the heat released in burning will rapidly raise the temperature of small particles nearby, and the large surface area presented by these particles encourages more reaction to take place and hence more heat to be produced. A runaway reaction can be the result. 

The trace elements present in the atmosphere which are dispersed in aerosols or associated with particulate matter are eventually removed by precipitation in rainfall or by gravitational fallout. There is, therefore, a continual transfer of trace-element contaminants from the atmosphere into the hydrosphere or into the soil, so that the air tends to be restored to an unpolluted state by natural processes. Air, therefore,provides a route for the contamination of the rest of the biosphere by trace elements discharged in smoke and fumes. 

Aerosols using an insoluble gas are not intended to be shaken before use. Shaking causes some of the propellant to be dispersed in the Hquid concentrate. Although the product may then be dispersed to a greater extent, greater loss of propellant also results. If enough propellant is lost, the product win become inoperative. 

If the dmg is not soluble in the propellant, it is dissolved or dispersed in a Hquid vehicle. The propellant then constitutes the third phase of the system, and the container must be shaken before valve actuation. Emulsified aerosol products like lotions and creams are examples of such systems. 

Because of their hydrophobic nature, siUcones entering the aquatic environment should be significantly absorbed by sediment or migrate to the air—water interface. SiUcones have been measured in the aqueous surface microlayer at two estuarian locations and found to be comparable to levels measured in bulk (505). Volatile surface siloxanes become airborne by evaporation, and higher molecular weight species are dispersed as aerosols. 

AEROSOL A colloidal suspension of liquid or solid particles dispersed in gas. 

Scheuch, G., and Stahlhofen, W. (1992). Deposition and dispersion of aerosols in the airways of the human respiratory tract the effect of particle size. Exper. Lung Res. 18, 343-358. 

Aerosols are small particles dispersed in gas. In aerosols, the particles are relatively large compared with the gaseous particles. 

Disperse systems can be classified in various ways. Classification based on the physical state of the two constituent phases is presented in Table 1. The dispersed phase and the dispersion medium can be either solids, liquids, or gases. Pharmaceutically most important are suspensions, emulsions, and aerosols. (Suspensions and emulsions are described in detail in Secs. IV and V pharmaceutical aerosols are treated in Chapter 14.) A suspension is a solid/liquid dispersion, e.g., a solid drug that is dispersed within a liquid that is a poor solvent for the drug. An emulsion is a li-quid/liquid dispersion in which the two phases are either completely immiscible or saturated with each other. In the case of aerosols, either a liquid (e.g., drug solution) or a solid (e.g., fine drug particles) is dispersed within a gaseous phase. There is no disperse system in which both phases are gases. 

Dry powder aerosols are more complicated to sample as the commercially available devices disperse the aerosol on the patient s inspiratory flow. In order to challenge the efficiency of these devices, it is important to sample at multiple flow rates. The standard flow rate has become 60 L/min. Additional flow rates of 30 (28.3) and 90 L/min have also been employed. Each impactor must be calibrated at the different flow rates employed. In recent compendial specifications the duration of sampling (4 s) and pressure drop across the device (4 kPa) has also been suggested. This corrects for the effort on the part of a patient in a single breath. 

Due to the volatile nature of most pulmonary agents, there is minimal extended risk except in an enclosed or confined space. Vapors have a density greater than air and tend to collect in low places. Solids that are dispersed as aerosols have little or no vapor pressure. Once the aerosols settle, there is minimal extended hazard from the agents unless the dust is resuspended. 

A colloid is a broad category of mixtures, and is defined as one phase suspended in another. A perfume spray is made up of a liquid (the perfume) dispersed in a gas (the air). The principle underlying the perfume atomizer is the same as the nozzle on a can of polish, and the jets within the carburettor in the internal combustion engine. In each case, the colloid formed is an aerosol. 

Whipple, R. T., W. R. Chen, and C. S. Wang. The Dispersion of Aerosol Boluses in a System of Repeatedly Branching Tubes. Paper No. 19-D Presented at the 75th Meeting of the AIChE (American Institute of Chemical Engineers), Detroit, Mich., June 3-6, 1973. 21 pp. 

Drugs can be sprayed in aerosol form onto mucosal surfaces of body cavities accessible from the outside (e.g., the respiratory tract [p. 14]). An aerosol is a dispersion of liquid or solid particles in a gas, such as air. An aerosol results when a drug solution or micronized powder is reduced to a spray on being driven through the nozzle of a pressurized container. 

An interesting application of small water drops is in the binding of dust in coal mines. It is, however, necessary to prevent the evaporation of the aerosol of water by previously dispersing in the water a little cetyl alcohol. The spray of water drops, each about 12 microns in radius, is then relatively stable, though without the cetyl alcohol complete evaporation occurs in a few seconds (d). A fuller account of evaporation may be found in Chapter 7 of reference 1. 

Colloid chemistry investigates substance mixtures. These substance mixtures can be heterogenous, such as emulsions (in which tiny droplets of one liquid are dispersed in another), suspensions (consisting of a fine dispersion of solid particles in a liquid volume phase), and aerosols (in which liquid droplets are dispersed in the gas phase). However, there are also homogenous mixtures in which the solute is present in larger, supermolecular aggregates. These homogenous mixtures include micellar solutions and liquid crystalline... 

There are other aerosol methods which can yield uniform powders, such as by dispersing aqueous dispersions of particles (e.g. of latex) and evaporating the water (12). In this case each droplet should contain only one particle, a task not easily accomplished. Alternatively, it is possible to nebulize solutions of electrolytes or other substances, which on removal of the liquid result in solid particles, dispersed in the carrier gas (13,14). This process has been expanded to include sintering of resulting solid aerosols in a continuous process to produce powders for various applications (15-18). 

Small particles (10 6 to 10 8 m range) dispersed in a liquid (hydrosols in water, organosols in an organic solvent) or gaseous (aerosol) medium. 

Darquenne, C., Brand, P, Heyder, J., and Paiva, M. (1997). Aerosol dispersion in human lung comparison between numerical simulations and experiments for bolus tests. J. Allied Physiol., 83, 966-974. 

Louey MD, Stewart PJ. Particle interactions involved in aerosol dispersion of ternary interactive mixtures. Pharma Res 2002 19(10) 1524—1531. 

---