Effects of dissolved polymer on the transport of colloidal particles in a microcapillary

Effects of dissolved polymer on the transport of latex particles through a microcapillary were investigated. The capillary hydrodynamic fractionation (CHDF) experiments carried out using poly(ethylene oxide) (PEO) solutions as the eluant showed an increase in the particle separation factor as well as a decrease in the degree of axial dispersion when the molecular weight of the PEO was increased. To some extent, this separation factor enhancement effect resulted from the enlargement of the effective particle diameter due to the adsorption of PEO on particles.; The occurrence of polymer adsorption was confirmed by performing dynamic light scattering on the polystyrene (PS) latex particles dispersed in the PEO solutions. The results showed the expected increase of the particle size depending on the molecular weight of the PEO.; PEO-adsorbed particle was modeled as a composite sphere with a solid core surrounded by a permeable porous shell. The drag force was computed and related to the diffusivity of the composite particle. The CHDF dynamic simulation performed using the composite particle predicted a lower degree of axial dispersion compared to a hard sphere of the same size.; Migration of particles in PEO solutions was also investigated using CHDF. Experiments performed with PEO solutions using the latex particles pre-adsorbed with Brij35SP surfactant to prevent the change of particle size because of PEO adsorption. The results suggested that the significant increase of the separation factor arose from the viscoelastic effect of the PEO solution. The particle migration velocity due to this effect was incorporated into the CHDF model and it was found to agree well with the experimental results.