Abstract
Dynamic light scattering (DLS) is commonly used for the determination of average particle diameters and suspension stability and popular in academics and industry. However, DLS is not considered suitable for polydisperse samples. The presence of little quantities of micrometre particles in nano and submicrometre suspensions especially affect the reliability of DLS results. Microfiltration might be a suitable method for the removal of unwanted large particles. This study investigates the effect of microfiltration on the diameter distributions as measured by DLS. Polystyrene standards (40–900 nm diameter), and monomodal silica suspensions were filtered with polytetrafluoroethylene (PTFE) membranes (0.1–1.0 µm pore size) to investigate retention properties and grade efficiency. Non-ideal materials were used to prove the results. Experiments showed that a mono-exponential decay can be achieved by filtration. A size safety factor of at least three between labeled pore size and average diameter was found to keep separation as low as possible. Filtration in order to enhance DLS for particulate submicrometre materials was considered suitable for narrowly distributed coated titania and kaolin powder. In a regulatory context, this might have an impact on considering a substance false positive or false negative according to the European Commission (EC) recommendation of a definition of the term nanomaterial.
Highlights
Dynamic light scattering techniques (DLS) have been used for many years in nanoparticle research
The determination of particle diameters and particle size distributions (PSD) by DLS is quite fast, and this technique is applicable to most colloidal dispersions [1]
This study investigates the performance of preparative filtration of nano- and submicrometre suspensions for the purpose of PSD analysis by means of DLS
Summary
Dynamic light scattering techniques (DLS) have been used for many years in nanoparticle research. The determination of particle diameters and particle size distributions (PSD) by DLS is quite fast, and this technique is applicable to most colloidal dispersions [1]. DLS measures the intensity fluctuation of light scattered from a sample of diffusing particles. Particle diameters determined by DLS refer to the hydrodynamic equivalent diameter, and PSDs are intrinsically intensity-weighted, even though a conversion to number- or volume-weighted distributions can be carried out. The simple application of Mie’s scattering theory is associated with assumptions. Algorithms to overcome these issues have been published—algorithms for figuring out how to calculate the hydrodynamic diameters of highly aggregated materials and how to determine the size distribution of microgel suspensions, for example [11,12,13]
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