Atomic force microscopy studies of membrane–solute interactions (fouling)

AFM has been proved to be a rapid method of assessing membrane–solute interactions (fouling) of membranes under process conditions. The interactions of developmental membranes (SPEEK/PSU and PSU) with different solutes have been directly measured and linked to process performance. Correlation of the performance of two commercial PCI membranes (ES404 and EM006) with AFM measurements has been carried out for two types of separation of industrial importance: ultrafiltration in the pulp and paper industry and protein concentration/ fractionation. AFM expertise has been further exploited in a study of the efficiency of membrane cleaning after a process of whey concentration.

AFM has proved to be one of the key techniques for membrane characterisation. AFM imaging in conjunction with force measurements can give very detailed information on the nature of membrane/solute interactions that is useful in the prediction of the process performance of membranes for relevant separations. The change in surface roughness and adhesion properties of membranes may be used as an indicator of the propensity of a membrane to foul during cross flow filtration at given conditions. The AFM results correlate well with industrial operating performance of the membranes. In the future, it should be possible to use the techniques developed to allow prior assessment of the fouling propensity of process streams with different types of membranes. This should allow optimum selection of a membrane without the need for pilot plant tests. In addition, the expertise developed has application across a wide range of technologies.