Chapter 4 - Investigating Membranes and Membrane Processes with Atomic Force Microscopy

Abstract

This chapter concerns pressure-driven membrane processes—microfiltration, ultra filtration, nanofiltration, and reverse osmosis. Membrane processes are one of the most significant developments in process engineering in recent times. Membranes find widespread application in fields as diverse as water treatment, pharmaceutical processing, food processing, biotechnology, sensors, and batteries. Membranes are most usually thin polymeric sheets, having pores in the range from the micrometer to subnanometer, which act as advanced filtration materials. Atomic force microscopy (AFM) is one means of imaging objects of dimensions from about the wavelength of light to those below a nanometer. Thus, in the case of membranes, it is possible to visualize the membrane surface properties, such as pores and morphology, using AFM. The chapter reviews the potential of AFM for the investigation of membranes and membrane processes using illustrative examples that outline the range of possibilities of AFM studies for membrane technology. Some more advanced topics are considered, such as the correspondence between surface pore dimensions from AFM and MWCO (molecular weight cut-off); imaging in liquid and the determination of surface electrical properties; effects of surface roughness on interactions with particles; ‘visualization’ of the rejection of a colloid by a membrane pore, and the use of AFM measurements in membrane development.