5.7 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Dynamic light scattering | 4/4 | https://en.wikipedia.org/wiki/Dynamic_light_scattering | reference | science, encyclopedia | 2026-05-05T10:04:18.544311+00:00 | kb-cron |
=== CONTIN algorithm === An alternative method for analyzing the autocorrelation function can be achieved through an inverse Laplace transform known as CONTIN developed by Steven Provencher. The CONTIN analysis is ideal for heterodisperse, polydisperse, and multimodal systems that cannot be resolved with the cumulant method. The resolution for separating two different particle populations is approximately a factor of five or higher and the difference in relative intensities between two different populations should be less than 1:10−5.
=== Maximum entropy method === The Maximum entropy method is an analysis method that has great developmental potential. The method is also used for the quantification of sedimentation velocity data from analytical ultracentrifugation. The maximum entropy method involves several iterative steps to minimize the deviation of the fitted data from the experimental data and subsequently reduce the χ2 of the fitted data.
== Scattering of non-spherical particles == If the particle in question is not spherical, the rotational motion must be considered as well because the scattering of the light will be different depending on orientation. According to Pecora, rotational Brownian motion will affect the scattering when a particle fulfills two conditions; they must be both optically and geometrically anisotropic. Rod-shaped molecules fulfill these requirements, so a rotational diffusion coefficient must be considered in addition to a translational diffusion coefficient. In its most succinct form, the equation appears as
A
B
=
5
4
4
M
p
+
2
N
M
l
M
p
+
M
l
M
p
−
N
+
M
l
{\displaystyle {\frac {A}{B}}={\frac {5}{4}}{\frac {4\mathrm {M} _{p}+2\mathrm {N} \mathrm {M} _{l}\mathrm {M} _{p}+\mathrm {M} _{l}}{\mathrm {M} _{p}-\mathrm {N} +\mathrm {M} _{l}}}}
Where A/B is the ratio of the two relaxation modes (translational and rotational), Mp contains information about the axis perpendicular to the central axis of the particle, and Ml contains information about the axis parallel to the central axis. In 2007, Peter R. Lang and his team decided to use dynamic light scattering to determine the particle length and aspect ratio of short gold nanorods. They chose this method since it does not destroy the sample and it has a relatively easy setup. Both relaxation states were observed in VV geometry and the diffusion coefficients of both motions were used to calculate the aspect ratios of the gold nanoparticles.
== Applications == DLS is used to characterize the size of various particles including proteins, polymers, micelles, Protein cages and virus-like particles, vesicles, carbohydrates, nanoparticles, biological cells, and gels. If the system is not disperse in size, the mean effective diameter of the particles can be determined. This measurement depends on the size of the particle core, the size of surface structures, particle concentration, and the type of ions in the medium. Since DLS essentially measures fluctuations in scattered light intensity due to diffusing particles, the diffusion coefficient of the particles can be determined. DLS software of commercial instruments typically displays the particle population at different diameters. If the system is monodisperse, there should only be one population, whereas a polydisperse system would show multiple particle populations. If there is more than one size population present in a sample then either the CONTIN analysis should be applied for photon correlation spectroscopy instruments, or the power spectrum method should be applied for Doppler shift instruments. Stability studies can be done conveniently using DLS. Periodical DLS measurements of a sample can show whether the particles aggregate over time by seeing whether the hydrodynamic radius of the particle increases. If particles aggregate, there will be a larger population of particles with a larger radius. In some DLS machines, stability depending on temperature can be analyzed by controlling the temperature in situ.
== See also ==
== References ==
== External links == DLS to determine the radius of small beads in Brownian motion in a solution Particle sizing using DLS Dynamic Light Scattering for particle size characterization of proteins, polymers and colloidal dispersions Understanding Dynamic Light Scattering, Wyatt Technology