![]() Therefore, the onset of sedimentation indicates the upper size limit for DLS measurements. If there is sedimentation, there is no random movement, which would lead to inaccurate results. A basic requirement for the Stokes-Einstein equation is that the movement of the particles needs to be solely based on Brownian motion. Further, the equation includes the viscosity of the dispersant and the temperature because both parameters directly influence particle movement. The speed of the particles is given by the translational diffusion coefficient D. The relation between the speed of the particles and the particle size is given by the Stokes-Einstein equation (Equation 1). If you know all other parameters which have an influence on particle movement, you can determine the hydrodynamic diameter by measuring the speed of the particles. As a result, smaller particles are moving at higher speeds than larger particles. The energy transfer is more or less constant and therefore has a greater effect on smaller particles. These collisions cause a certain amount of energy to be transferred, which induces particle movement. The principle of Brownian motion is that particles are constantly colliding with solvent molecules. When particles are dispersed in a liquid they move randomly in all directions. Users should refer to the original published version of the material for the full abstract.Dynamic light scattering (DLS) is based on the Brownian motion of dispersed particles. No warranty is given about the accuracy of the copy. However, users may print, download, or email articles for individual use. Copyright of Journal of Nanoparticle Research is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission.These results overall are intended to bring essential improvements and to stimulate reexamination of the metrological capabilities and role of DLS in nanoparticle characterization. We also investigate the extent to which the DLS polydispersity descriptors are representative of the distributional quality and find them to be unreliable and misleading, both for monodisperse reference materials and broad-distribution biomedical nanoparticles. We explicitly identify and validate the harmonic mean as the central value of the intensity-weighted DLS size distribution that expresses the inversion results consistently with the cumulant results. The resulting discrepancies are typically larger than 15% depending on the polydispersity index of the samples. Through the measurement of monomodal nanoparticle samples having an extensive range of sizes (5 to 250 nm) and polydispersity, we similarly demonstrate that the default outputs of a frequently used DLS inversion method are ill chosen, as they are regularizer-dependent and significantly deviate from the cumulant z-average size. Central values obtained incautiously from this representation often lead to significant interpretation errors. We address the misleading way DLS size distributions are often presented, that is, as a logarithmically scaled histogram of measured relative quantities. Here, we critically discuss the application of DLS for nanoparticle characterization and provide much-needed clarification for ambiguities in the mean-value practice of commercial DLS software and documentary standards. Abstract: Dynamic light scattering (DLS) is an essential technique for nanoparticle size analysis and has been employed extensively for decades, but despite its long history and popularity, the choice of weighting and mean of the size distribution often appears to be picked ad hoc to bring the results into agreement with other methods and expectations by any means necessary.
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