Settling radius diameter

The diameter of a sedimenting species determined from Stokes law assuming a spherical shape. Also referred to as the Stokes diameter or (divided by a factor of 2) the settling radius . 

Lest I leave the erroneous impression here that colloid science, in spite of the impossibility of defining it, is not a vigorous branch of research, I shall conclude by explaining that in the last few years, an entire subspeciality has sprung up around the topic of colloidal (pseudo-) crystals. These are regular arrays that are formed when a suspension (sol) of polymeric (e.g., latex) spheres around half a micrometre in diameter is allowed to settle out under gravity. The suspension can include spheres of one size only, or there may be two populations of different sizes, and the radius ratio as well as the quantity proportions of the two sizes are both controllable variables. Crystals such as AB2, AB4 and AB13 can form (Bartlett et al. 1992, Bartlett and van... 

In treating some closed interiors with aerosols, it may be necessary to limit the time of application. In this case the particle size must be large enough to settle out in the time available. A 10- to 15-minute exposure time is the minimum for satisfactory results. An aerosol spray having a mass median diameter of 15 to 30 microns is sufficient for the short-exposure applications, but will not penetrate so completely as the smaller particle size. Furthermore, aerosols of this size must be released from more than one point if the radius of the area is more than 15 feet. When heat from thermal generators causes excess breakdown of the insecticide, equipment that produces larger particle sizes must be used. 

A quantitative comparison of particle expansion determined by the three methods is given in Table I. The particle diamete of the standard acrylic latex was determined by PCS to be 1120 A. This value was used in the calculation of the increase in particle radius at maximum expansion in each case. The sedimentation method yielded the largest increase in radius, 302 A, followed by the viscometric value of 240 K. Possibly the shear involved in the latter method resulted in a partial collapse of the surface layer. The value determined by PCS was found to be approximately half that determined by sedimentation. Since the PCS determination is presumed to be free of particle interactions at a concentration of 5 X 10 4%, we must conclude that the other two methods (at 1% solids) exhibit such interactions. As a result, the charged particles settle slower (19) and yield a higher viscosity than in the absence of these (repulsive) interactions. 

A polystyrene particle settles, moving from a starting radius of 70 ntm to an analytical radius of 80 mm in 2.9 s in a centrifugal field of 9000 G. If the particle is in an aqueous solution at 20 what is the Stokes diameter ... 

The microscopic analysis of the synthesised suspensions showed that the BaS04 particles are anisometric (rods with a ratio of length to diameter of 4 1, which explains the sigmoidal appearance of the sedimentation inflection curves). At the initial phase of sedimentation, the rod-like particles may rotate, which provides additional resistance to their movement (similar to an increase in viscosity), and decelerates the sediment accumulation rate. Moreover, during free sedimentation, the aspherically formed particles provide maximum resistance to their own motion. This also decreases the sedimentation rate of the solid particles and complicates the definition of their true size. Therefore, the equivalent radius r (radius of spherical particle, settling at the same rate) was defined according to the results of sedimentation analysis. 

Once the functional relationship between the hydrodynamic diameters and the aggregate mass is known, one can establish simple models for the average dynamic properties (e.g. for the settling velocity) of suspensions containing aggregates. However, while the aggregate mass is well defined for numeric aggregates, it is difficult to measure in real-life experiments. It is more likely that the radius of... 

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