1. Light Scattering (pp. 53-63 in Shaw and pp. 193- 244 in Hiemenz and Rajagopalan) Introduction Rayleigh Scattering Debye Scattering, Zimm Plots Dynamic Light Scattering

2. Introduction Absorbed Transmitted Scattered Turbidity Information Obtained Particle mass non-perturbed absolute determination instantaneous Particle size and shape Dynamic information (diffusion constants) When there is no absorption

3. Rayleigh Scattering particles small (< /20, about 20-25 nm) refractive index similar to medium Debye Scattering particles relatively large refractive index similar to medium Mie Scattering few constraints on size or refractive index easily applied only to spherical particles, or particles where geometry is known (NOT discussed here)

4. Experimental Apparatus

5. Rayleigh Scattering Rayleigh found the following relationship for point scatterers (i.e. particle size < /20): Why is the sky blue? ( red =700 nm, blue =400 nm) Vertically vs. horizontally polarised light Insert Shaw Fig. 3.6

6. Assumptions scatterers are isotropic,dielectric, non-absorbing n is not too large size of scatterers is small cf. light wavelength Find an expression for  and replace in the Rayleigh equation...

7. Comparison to osmotic pressure measurements: Instantaneous, kinetics possible covers a different particle size range Debye Scattering If particle size> /20 we get interference effects... Use a correction factor P(  )

8. Correction term derived from X-ray scattering theory... Physical meaning of radius of gyration... average radius swept out by a chain of n particles (e.g. polymer, protein…) centre of mass n1n1 n3n3 n2n2 r1r1 r3r3 r2r2

9. Zimm Plots No interference effect, just like Rayleigh eqn. slope gives i.e. particle size info. particle MW info--Zimm plot 2B c=0  =0 (+ Overheads)

10. Dynamic effects