By this time the Rayleigh–Gans–Debye (RGD) theory was established that included scattering from large particles however, Zimm’s ( 1945 1948) modifications to RGD equations led the foundation of modern light-scattering approaches that are being utilized to determine size, shape, and molecular weight of macromolecules in solution. Cabannes and Rocard ( 1929) and Gans ( 1921 1923) addressed the theory of optically anisotropic scatters as well as their influence on polarisation of scattered light. However, until this point the role of optical anisotropy on angular dependence, intensity, and polarization of scattered light had not been studied.
At the same time, William Sutherland also presented a very similar derivation of the Stokes–Einstein equation independently (Sutherland 1905). Later, Einstein also established a relationship between the diffusion coefficient of particles to their translational friction by including the discovery from Sir George Stokes ( 1845) that suggested that the friction exerted by a moving particle is proportional to its radius and to the viscosity of the solvent surrounding particles (Einstein 1906). He established that particles were subjected to random forces due to constant collision with solvent molecules resulting in random walk of particles, and that the mean squared displacement of particles due to Brownian motion is proportional to time. Einstein ( 1905) also established Brownian motion theory (named after Robert Brown) explaining molecular motion of particles. Einstein and Smoluchowski proposed that liquid should be considered as a continuous medium where thermal fluctuations create inhomogeneities, which result in density and concentration fluctuations (Fluctuation theory of light scattering, Einstein ( 1910) v.
#THEORY OF DYNAMIC LIGHT SCATTERING SERIES#
The usefulness of light scattering as a method to characterize the diffusion behaviour of particles in solution resulted from a series of seminal discoveries.
Peter Debye suggested that scattering for particles can be studied independently of assumptions on mass, size, or shape as a function of angle (Debye 1915), which is often referred as Rayleigh–Debye scattering. In contrast to Rayleigh theory, Gustav Mie ( 1908) described a theory (Mie theory) to study the scattering of light from absorbing and non-absorbing particles that are large compared to the wavelength of light by taking into account particle shape and the difference in refractive index between particles and the medium the particles are present in. Soon after, Lord Rayleigh described light scattering from particles that are smaller than the wavelength of light (Rayleigh scattering), which explained both that the sky’s blue colour is a result of scattering of light due to atmospheric particles and that the refractive index of the scattering medium plays a crucial role in light scattering (Strutt 1871a, b). One of the earliest light-scattering experiments was described by John Tyndall, which characterized light scattering from colloidal suspensions (Tyndall effect), where particles are larger than the wavelength of the incident light (Tyndall 1868).
In a typical light-scattering experiment, sample is exposed to a monochromatic wave of light and an appropriate detector detects the signal. Detection of light scattering from matter is a useful technique with applications in numerous scientific disciplines where, depending on the light source and detector, specific properties of molecules can be studied.
0 kommentar(er)
