Diffusion constants sediments

The presence of particles in the fluid medium complicates diffusion in a sediment due to the effects of porosity, represented by n, and tortuosity. Since tortuosity of natural sediments is seldom known it is more convenient to use the term "formation factor" or "lithological factor," denoted L, which takes into account everything but porosity. Tick s diffusion constant D is replaced by the whole sediment diffusion constant Ds, where < D. 

Table 8-7 Diffusion constants of sediments (Ds) for some common chemical species"...

The mass of the sedimenting particle could be deduced from its rate of sedimentation at high dilution in a given field, i.e., from its sedimentation constant, if the frictional coefficient / could be determined independently. Hates of diffusion may be utilized to secure this necessary supplementary information, since the diffusion constant D depends also on the frictional coefficient. Thus ... 

Experimental results are consistent with this relation, but inaccuracies in sedimentation constants preclude precise evaluation of the empirical exponent. Similarly, the diffusion constant at infinite dilution, given by... 

Sedimentation- diffusion Absolute fairly fast Requires 3 separate determinations (diffusion coefficient, sedimentation constant and partial specific volume) <5... 

Conformation in solution is indicated by the way in which the hydro-dynamic properties of the macromolecules change with change in molecular weight. From trends in the intrinsic viscosity, the sedimentation coefficient, or the diffusion constant with molecular weight we can learn something about the conformation of the molecule in solution (19,20). 

The reason for using the two different molecular weights is that some properties, such as freezing points, vapor pressure, and osmotic pressure of dilute solutions, are related directly to M , whereas other properties, such as lightscattering, sedimentation, and diffusion constants, are related directly to Mu-... 

The value of 483,000 is in the original publication but was misquoted by both Sumner (1) and Varner (3) as 473,000. Moreover, the diffusion constant was determined in the presence of sodium sulfite but the sedimentation constant was not. The main component in phosphate buffer was found to have a sedimentation constant of 18 5 at 20°. 

The diffusion constant D is a function of both molecular weight and shape. It can be measured by observing the spread of an initially sharp boundary between the protein solution and a solvent as the protein diffuses into the solvent layer. Once we know the value of the diffusion constant, we can combine the information with the sedimentation data and calculate the molecular weight of the protein. 

The behavior of filamentous molecules in sedimentation equilibrium measurements is not ideal. Attempts have been made to overcome this by taking into account the dependence of sedimentation and diffusion constants on concentration17 and also the deviations from ideal behavior of each component in the mixture.82... 

The levan from Bacillus vulgatus has been studied in the ultracentrifuge by Ingelman and Seigbahn.62 The values of the sedimentation and the diffusion constants obtained indicated molecular weights of 50-100 million (S20 = (200-300) 10 13 D2o = 0.2(10)-7), these values being unaltered even if the levan was precipitated with alcohol, dried and redissolved. 

The auto-hydrolytic effect of boiling an aqueous solution was also investigated by following changes in the sedimentation and diffusion constants and the intrinsic viscosity. Although the measurements were complicated by the fact that the insoluble portion dissolved as boiling proceeded, the results indicated that the gum molecules were long chains with small adjacent side chains, and that hydrolysis attacked the weaker side chains. 

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