Abhishek Roy

Dow Chemical: Materials Science Contributions to Membrane Production

In this chapter, authors present a review of technical developments in reverse osmosis membranes and module technology and ultrafiltration membranes and module technology. State of the art of these technologies, potential future research opportunities and impact areas are also discussed.

Electron tomography reveals details of the internal microstructure of desalination membranes

Significance The development of membrane materials is limited by our lack of tools to characterize their complex microstructure. We demonstrate how a combination of careful sample preparation, electron tomography, and quantitative analysis of 3D models can provide unique insights into the morphology of polyamide active layers used in reverse osmosis membranes. Extracting the 3D morphology is required to obtain accurate estimates of the top surface area and internal void fraction. Furthermore, mapping the internal heterogeneity shows that polymer density is highest near the top surface and suggests new models of how microstructure and membrane performance is connected. As water availability becomes a growing challenge in various regions throughout the world, desalination and wastewater reclamation through technologies such as reverse osmosis (RO) are becoming more important. Nevertheless, many open questions remain regarding the internal structure of thin-film composite RO membranes. In this work, fully aromatic polyamide films that serve as the active layer of state-of-the-art water filtration membranes were investigated using high-angle annular dark-field scanning transmission electron microscopy tomography. Reconstructions of the 3D morphology reveal intricate aspects of the complex microstructure not visible from 2D projections. We find that internal voids of the active layer of compressed commercial membranes account for less than 0.2% of the total polymer volume, contrary to previously reported values that are two orders of magnitude higher. Measurements of the local variation in polyamide density from electron tomography reveal that the polymer density is highest at the permeable surface for the two membranes tested and establish the significance of surface area on RO membrane transport properties. The same type of analyses could provide explanations for different flux variations with surface area for other types of membranes where the density is distributed differently. Thus, 3D reconstructions and quantitative analyses will be crucial to characterize the complex morphology of polymeric membranes used in next-generation water-purification membranes.