Static Light Scattering

In Static Light Scattering a beam of polarized light is focused onto a polymer/particle and the scattered light is detected with a photodiode detector. In Static Light Scattering the intensity of this scattered light is measured, which is proportional to the molar mass and the concentration of the particles or polymers in solution. In Static Light Scattering the accessible molar mass range is ca. 10³ Da to 10⁹ Da and the particles size range covered is ca. 10 nm to 500 nm. Because in Static Light Scattering the intensity of the scattered light is directly proportional to the product of molar mass (Mw) and sample concentration (c) the following formula can be used to describe the phenomena:

I_LS ~ M_w * c

I_LS = Light scattering intensity; M_w = Molar mass weight-average; c = Sample concentration

In more detail Static Light Scattering in dilute polymer solutions can be expressed by the following equation:

[(K’ * c) / R(θ)] = [1 /(M_w * P(θ)] + [2 * A₂ * c]

R(θ) = Excess intensity of scattered light at a given angle (θ);
c = Sample concentration
M_w = Molar mass weight-average
A₂ = Second viral coefficient
K’ = Optical constant equal to 4π²n² (dn/dc)² / (λ_o⁴N_A)
P(θ) = Function describing the angular dependence of the scattered light

If one incorporates some defined assumptions and approximations, e.g. dilute solutions, single angle detection, molecules small compared to wavelength of light, then the equation above can be simplified to the following formula:

[(K’ * c) / R(θ)] = [1 / M_w]

This means that by using Static Light Scattering the molar mass of a macromolecule can be calculated when the detector constant K’ has been determined and the sample concentration and the intensity of the scattered light is measured.

For more information about Static Light Scattering contact Postnova Analytics via telephone, fax, email or visit our homepage www.postnova.com !

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