Sub-micron particle analysis by thermal field-flow fractionation and multi-angle light scattering detection

Thermal field-flow fractionation (ThFFF) coupled to multi-angle light scatt ering (MALS) detection has been used to analyse sub-micron particles. Polys tyrene and styrene-butylmethacrylate latices of various composition were st udied as well as different swellable core-shell particles. Using ThFFF-MALS , thermal diffusion coefficients (D-T) of particles could be calculated dir ectly without need for additional dynamic light scattering (DLS) measuremen ts. The Soret coefficient was determined from ThFFF data while MALS provide d the particle radius of gyration allowing calculation of the particle diff usion coefficient. Combining both data gave the thermal diffusion coefficie nt It was demonstrated that differences in the particle chemical compositio n can lead to differences in thermal diffusion. However, no clear trend was observed, and as thermal diffusion is still poorly understood, it is diffi cult to correlate chemical composition with D-T. Apart from the influence o f the chemical composition of the particles, it was found that the pH of th e carrier solution also had a strong effect on thermal diffusion. Although thermal diffusion will be mainly determined by the particle surfac e composition, study of core-shells showed that swelling of the outer layer of the particle does not significantly influence thermal diffusion. To calculate diffusion coefficients for complex core shells, DLS measuremen ts were still required. Combination of DLS and ThFFF-MALS data gave insight into the swelling behaviour of core-shells and their internal structure.