Colloids organic aerosols

Hygroscopic, Surface, and Colloidal Properties of Organic Aerosols 474... 

So far, we have prepared and tested many kinds of colloids, mainly in nonaqueous suspensions with combinations of metals or alloys as a dispersed phase and organic liquids as the dispersion media, without the use of any dispersing agents these are listed in Table 9.4.1. We next give some examples of transmission electron micrographs of nanoparticles produced by an aerosol method. A sample for TEM measurement was obtained by dropping colloidal suspension onto a Cu mesh coated with an evaporated carbon film of 10 nm thickness. Many colloids were so unstable... 

Tpo understand the physical and colloidal chemical aspects of pesticidal formulations research, one must first understand the objectives of the formulations chemist in his work. Simply speaking, the formulations chemist must take the pure organic chemical pesticide and put it in a usable form for field use. These forms include wettable powders, emulsifiable concentrates, dusts, granules, water-soluble concentrates, flowables, and an aerosol, to name a few types of concentrates. The formulations chemist desires to put together a formulation that (1) is easy and eco-... 

The concept of air as a colloid and the term aerosol for air containing an assembly of suspended particles were originally introduced by Schmauss and Wigand (1929). Colloids are inherently stable because fine particles are subject to Brownian motion and resist settling by sedimentation. The individual aerosol particles may be solid, liquid, or of a mixed variety, and all types are found in the atmosphere. Solid particles in the air are called dust. They are primarily formed by the erosion of minerals at the earth surface and enter the atmosphere by wind force. Sea spray from the ocean surface provides a prolific source of liquid droplets, which upon evaporation produce sea-salt crystals or a concentrated aqueous solution thereof. Solid and liquid particles also arise from the condensation of vapors when the vapor pressure exceeds the saturation point. For example, smoke from the open and often incomplete combustion of wood or agricultural refuse arises at least in part from the condensation of organic vapors. 

Fatty acid film formation and the associated surface tension depression has been studied extensively for idealized systems (i.e., pure water subphases) by the colloid science community, starting with the work of Langmuir nearly a century ago [211, 212]. Since it is known that fatty acid phase behavior depends strongly on factors such as pH, the presence of salts, and mixed organic content [6, 213, 214], it is not possible to extrapolate measurements performed in pure water or very dilute systems to the relevant aerosol conditions. Here we focus on studies which move towards more atmospherically relevant systems. The results of several studies are summarized in Table 4. 

A dispersion is instead a mixture in which the less abundant compound is dispersed, but not molecularly dissolved, in the other component. Examples are a dispersion of a solid phase (powder, nanoparticles, nanocrystals, nanotubes, etc) in a solvent, which is called a suspension, or a dispersion of an immiscible liquid phase in a second liquid, which is called an emulsion. Milk and mayonnaise are familiar examples of emulsions. Aerosols are dispersions of tiny liquid droplets or solid particles in a continuous gaseous phase. The science of aerosols is particularly relevant in order to design filter elements able to remove droplets and particles from air, which can be performed with very high efficiency by polymer nanofibers (Section 4.3.1). Finally, another way to indicate homogeneously mixed dispersions, emulsions or aerosols of nano- or microparticles is colloids. Colloidal dispersions of inorganic nanocrystals or organic nanofibers are familiar examples for nanotechnologists. 

The first important condition for efficient aerosol processing is to use stable colloidal dispersions or solutions, the so-called sok, as initial hquid phases to be sprayed. These suspensions/solutions must be sufficiently kinetically stable to allow processing of the full batch, which takes from few minutes to 1 h depending on the equipment. The sol precursor can be composed of dispersed dense or porous nanoparticles mixed with soluble sol-gel precursors, organic or hybrid... 

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