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Guinier Plot

The Guinier Plot allows the determination of the Radius of Gyration R_g from the measured scattered intensity I_s(q) as a function of the scattering vector q. It is used in X-Ray, neutron, and static light scattering (SLS). By applying a simple linear fit to the Guinier equation

\ln{I_s(q)} = \ln{I_i} - \frac{q^2 R^2_g}{3}

one obtains R_g. This is however only true for small scattering angles and within RGD limits:

  • Either scattering angle should be sufficiently small or the wavelength of the scattered wave (q R_g \ll 1)
  • The difference in refractive index of solvent and scattering unit should not be very large (m -1 < 0.3).
  • As is the case for all SLS measurements multiple scattering must be suppressed or the sample must be sufficiently dilute.

So for colloidal science, the RDG limits should be considered more carefully than for polymer science because the difference in relative refractive index is typically small between a polymer chain and the surrounding solvent.


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