Porous polymer nanoparticle layers

Abstract

Multilayers of colloidal polymer particles provide micro- or mesopores and can be used as a separation media similar to micro- and ultrafiltration membranes. Materials derived from polymer particles are of interest for making novel functional membranes, because they combine mesoporosity, high specific surface area and the possibility to apply functional groups on the outer and inner surface of the separation layer. The aim of the current work was to build up mesoporous multilayers of polymeric nanoparticles for testing its structural properties and certain separation performances. For these purposes different latices with average particle sizes between 20 and 80 nm were synthesised by emulsion polymerisation and the latices were further cleaned by dialysis and ion-exchange to remove surfactants. Some latices were further surface modified with a sulphonated reagent to produce highly charged particles. The latex particles were deposited on micro- and ultrafiltration membranes by a dead-end filtration process and the hydraulic cake resistances of the very thin nanoparticle layers (filter cake) were determined in filtration experiments. The Carman–Kozeny equation was used to derive the porosity of the layers. It was shown that the rejection of dextrane increased with decreasing average diameter of applied particles and the particle layers had molecular weight cut offs in the range of ultrafiltration membranes. The calculations using the data from filtration experiments show that the porosity of a layer obtained by the filtration process increases when smaller particles are applied and these calculations were confirmed by rejection experiments. The results on the cake resistances for different latices indicate that the surface properties of the nanoparticles applied strongly affect the cake properties and the mechanical stability of such a layer formed by filtration.