Z-average translational diffusion

The z-averag translational diffusion coefficient aj infinite dilution, D, could be determined by extrapolating r/K to zero scattering angle and zero concentration as shown typically in Figs. 4 and 5. D is related to the effective hydrodynamic radius, by the Stokes-Einstein relation ... 

This generates the first moment T, of the correlation function c(t) from which the z-averaged translational diffusion coefficient Dt,z computed... 

The infinite dilution z average translational diffusion coefficient may be used in equation (15) to calculate an effective coil diameter. This diameter which represents the effective spherical dimension of the polymer molecules undergoing translation has been used to calibrate SEC systems. ... 

QLS has been used routinely to determine the Z-average translational diffusion coefficient and the corresponding hydrodynamic radius of macromolecules in solutions and of colloidal suspensions (11,12) and also to characterize the polydispersity effects the method of cumulants (13). 

In dynamic light scattering (DLS), or photon correlation spectroscopy, temporal fluctuations of the intensity of scattered light are measured and this is related to the dynamics of the solution. In dilute micellar solutions, DLS provides the z-average of the translational diffusion coefficient. The hydrodynamic radius, Rh, of the scattering particles can then be obtained from the Stokes-Einstein equation (eqn 1.2).The intensity fraction as a function of apparent hydrodynamic radius is shown for a triblock solution in Fig. 3.4. The peak with the smaller value of apparent hydrodynamic radius, RH.aPP corresponds to molecules and that at large / Hs,Pp to micelles. 

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