Random movement, aggregation from

Reactivity in aggregates may be used to get useful infonnation on mobility in these systems. Vesicles are particularly amenable to these studies because, as mentioned earlier, mobihty in these aggregates is lower than in micelles. For instance, it is estimated that above T, lateral diffusion of the lipids within the plane of the vesicle bilayer is very fast (diffusion coefficient of 10 cm s , in the fluid phase), though three orders of magnitude slower than in an aqueous medium. Accordingly, randomization of a hpid in a leaflet of the bilayer of a 500 A vesicle will occur in milliseconds, whereas the slow transverse (flip-flop) movement from one leaflet to another may take up to several days [1, 7, 60]. 

A colloidal system is characterized by particles ranging in size from 1 mp to 0.1 p in diameter. They can be formed either by aggregation of small molecules like sodium chloride or by disintegration of large polymers. The particles are non-fllterable and can be observed under the ultramicroscope as Illuminated discs engaged in a kind of random zig-zag motion. This type of movement is called Brownian movement after the name of its discoverer Robert Brown. The smaller the particles, the more rapid is their movement. This unpredictable chaotic movement... 

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