Microfiltration of Submicron-Sized and Nano-Sized Suspensions for Particle Size Determination by Dynamic Light...

Area of Science:

• Materials Science
• Analytical Chemistry
• Nanotechnology

Background:

• Dynamic Light Scattering (DLS) is a widely used technique for determining particle size and suspension stability in academic and industrial settings.
• DLS accuracy is compromised by the presence of larger particles in nano- and submicrometre suspensions, leading to unreliable results.
• Microfiltration presents a potential method for removing these unwanted larger particles to improve DLS reliability.

Purpose of the Study:

• To investigate the impact of microfiltration on particle diameter distributions measured by DLS.
• To evaluate the effectiveness of microfiltration in removing larger particles from suspensions.
• To determine optimal filtration parameters for enhancing DLS analysis.

Main Methods:

• Filtration of polystyrene standards (40-900 nm) and monomodal silica suspensions using polytetrafluoroethylene (PTFE) membranes with pore sizes ranging from 0.1 to 1.0 µm.
• Analysis of retention properties and grade efficiency of the filtration process.
• Validation of results using non-ideal materials.

Main Results:

• Microfiltration successfully removed larger particles, enabling mono-exponential decay in DLS measurements.
• A minimum size safety factor of three (between membrane pore size and average particle diameter) was identified to minimize separation.
• Filtration proved suitable for improving DLS analysis of narrowly distributed coated titania and kaolin powder.

Conclusions:

• Microfiltration is a viable technique to enhance the reliability of DLS for analyzing submicrometre particulate materials.
• The findings have implications for regulatory assessments, particularly concerning the European Commission's definition of nanomaterials.
• Optimized microfiltration can prevent misclassification of substances as false positives or false negatives in nanomaterial assessments.