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HYFLON AD membranes are very interesting devices in water treatment and for their impermeability to water and gases and vapour transpirability [1]. In these kinds of processes, such in many large-scale processes, some membrane parameters are particularly important, among them: pore distribution, membrane morphology and their fouling tendency. The aim of the present work is to describe an AFM study of three different composite HYFLON AD 60X membranes characterising three key properties affecting performance: pore size distribution, surface morphology and particle adhesion. The membranes have been imaged at high resolution in NaCl solution, allowing quantification of surface roughness and pore size distribution. Further, the adhesion of polystyrene and silica particles to the membranes was measured in NaCl solution at three different concentrations to quantify their likely fouling tendencies.

This work has shown how AFM may be used to quantify the surface morphology of three composite membranes. High-resolution scanning allowed visualisation of pores and determination of pore size distributions. It was found that the mean pore diameters were between 18 and 40 nm. Care must be taken in the quantitative use of such results, but it is very satisfying that the relative pore sizes correspond to experimentally measured ones. Use of the colloid probe technique allowed quantification of the adhesion of polystyrene and silica particles to the membrane surfaces. Adhesion for polystyrene particles was greater than that on UF polysulphone membranes. Adhesion of silica particles was lower than that for polystyrene, due partly to electrostatic interactions and partly to short-range interactions. The direct AFM measurement of adhesion is especially valuable as at the present there is no adequate quantitative theoretical description of adhesion in solution taking into account shortrange interactions and surface roughness. AFM is a valuable technique for quantifying key properties of such membranes, both their fundamental form and their likely fouling properties.