Scattering intensity particle diameter

Additional evidence for silica nucleation on biopolymer macromolecules was furnished by experiments in which solutions of proteins were studied by dynamic light scattering. As an illustration, Figure 3.6 shows the relative intensity of light scattering versus the diameter of the scattering particles in solution with 1 wt.% of bovine serum albumin. Curve 1 presents the initial state where the protein was not yet treated with silica precursor. The measured... 

Fig. 3.6 The relative intensity of dynamic light scattering vs. the diameter of scattering particles for a solution with 1 wt.% bovine serum albumin (1) and the same solution after addition of 3 wt.% of THEOS (2). Before the measurements, the solutions were left at ambient temperature for a week. The drawings are a schematic representation of a protein macromolecule before and after the treatment by silica precursor.

The vesicle size is an important parameter not only for in-process control but particularly in quality assurance, because the physical stability of the vesicle dispersion depends on particle size and particle size distribution. An appropriate and particularly quick method is laser light scattering or diffraction. Laser light diffraction can be applied to particles > 1 pm and refers to the proportionality between the intensity of diffraction and the square of the particle diameter according to the diffraction theory of Fraunhofer. 

For particles below 200 nm, Rayleigh s theory holds, which considers the scattering intensity to be proportional to the 6th potency of the particle diameter. Both Fraunhofer s and Rayleigh s theories are only approximations of Mie s theory which claims that the scattering intensity depends on the scattering angle, the absorption, the size of the particles as well as on the refractive indices of both the particles and the dispersion medium. 

Figure 3. The scattering intensity, Cj, per particle as a function of particle diameter according to the exact Mie theory (solid line) and the Rayleigh Debye approximation (dotted line).

Figure 5. Scattering intensity per unit mass of particles as a function of particle diameter for a system in which the wavelength of the incident light is 632.8 nm, the scattering angle is 90°, the particle refractive index is 1.59, and the medium refractive index is 1.33 (for example polystyrene spheres in water).

Figure 2. Predictions of intensity per unit particle volume as a function of particle diameter for three scattering angles given Incident wavelength 514.5 nm and refractive index ratio polystyrene/water of 1.2.

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