(752d) Use of Asymmetric Flow-Field Flow Fractionation to Characterize Aggregating Colloidal Dispersions
The estimation of the size distribution of complex colloidal dispersions, such as dispersions of clusters of nanoparticles is a notoriously challenging task. Common characterization techniques include electron microscopy, light scattering, centrifugation, ultrasound spectroscopy etc.. Most of the above mentioned techniques, as for light scattering, provide some average size of the dispersion, but the reconstruction of the entire size distribution is often an ill-posed problem. Other techniques, like electron microscopy, are capable of analyzing individual particles and clusters, and can provide detailed information about the distribution, but require long times and require to dry the sample, a harsh process which can alter the structure of delicate clusters. Flow Field Flow Fractionation, on the other hand, is a well established chromatographic technique able to fractionate mixtures of colloidal nanoparticles having different sizes under gentle conditions. Usually, the extraction of a size distribution is carried out by analyzing the elution times of the samples and by estimating their hydrodynamic radii using a calibration curve. In this work, we make use of Asymmetric Flow Field Flow Fractionation coupled to a two angle static light scattering detector (SLS) to characterize suspensions of different polymeric colloidal nanoparticles undergoing stagnant aggregation under both diffusion and reaction-limited conditions. Two types of particles have been used: rubbery fluorinated colloids undergoing coalescence and hard polystyrene latexes forming fractal clusters. The cluster size distribution is quantitatively reconstructed not from the elution times, but from the analysis of the SLS data, which requires the knowledge of the scattering properties of both clusters and particles. The estimated cluster size distributions favorably compare with the calculated ones from Population-Balance-Equations. These results prove the effectiveness of AF4 in combination with multi-angle light scattering as a tool to quantitatively characterize the size distribution of complex colloidal dispersions.