Organic colloidal materials, particle size ranges

Once these colloidal particles are in hand, the next challenge is to assemble them into larger scale superstructures. A promising class of such materials obtained by self-assembly is the colloidal crystals, ordered arrays of particles in the nanometer- to micrometer-size range. However, because the materials obtained after colloidal crystals are dried are brittle and can be redispersed in water, replication is necessary. In addition, the size and shape of the colloidal crystal needs to be controlled on a macroscopic scale. Several ways have been developed to control the organization of colloidal assembhes by using flow, surface tension forces, or electrical fields. 

All natural waters contain some carbonaceous material. Even rainwater has been shown to include about 1 mg C/L (Thurman, 1985). Some of this organic material is in the form of truly dissolved, soluble compounds, whereas other fractions consist of colloidal or particulate organic matter. The definitions of dissolved and particulate carbon that have been more or less established by convention among aquatic scientists are somewhat elastic and arbitrary one criterion that is widely used sets the boundary between the two at 0.45 /tM (the pore size of some common filter media). These demarcations tend to disguise the fact that there is a continuum of organic particles in water that ranges in relative size from molecules to microorganisms. 

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