This study introduces a general method of asymmetrical flow field-flow fractionation (AF4) for pa...

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Project of Characterization of Nanoparticle Diameter using Asymmetrical Flow Field-Flow Fractionation

This study introduces a general method of asymmetrical flow field-flow fractionation (AF4) for particle size measurement of polystyrene latexes.

AF4 is an analytical-scale elution technique where particles are separated in a thin ribbon-like channel on basis of diffusion coefficient (or particle size). The separation takes place under the influence of flow field generated by a cross flow where 0.1% SDS and 0.02% NaN3 aqueous solution act as carrier phase. Due to laminar parabolic flow in the channel with flow velocity increasing from near zero at the channel walls to a maximum at the centre of the channel, the samples latex particles suspended at the same carrier liquid with different difusion coefiicient pass through the channel chamber with different retention time. Besides, the particle diameter can be directly determined from the measured retention time. Several AF4 experimental parameters are optimized including focusing time, cross flow rate, injection mass and channel flow rate, which are important to quantify the actual values. Meanwhile, the scanning electron microscope (SEM) technique is also utilized for particle characterization in which the particle sizes are calculated based on ratio of their diameters to the SEM magnification scale from its SEM image.

The results are compared with characterization through the AF4. It is found that AF4 is particularly useful and simple for the determination of particle size, because elution profile could be converted to particle size on the basis of an equation directly. Each sample is injected ten times and the relative standard deviation in the measured mean diameters is less than 1%. SEM yielded a mean diameter that is lower than those obtained from AF4 or provided by manufacturers, probably due to shrinkage of particles during sample drying and high-vacuum measurements. Therefore AF4 is more accurate and precise than SEM, which can be developed as an accurate method for size characterization.