A new in situ method for the characterization of membranes in a wet state in the environmental scanning electron microscope

This work presents a new microscopic method for the characterization of microfiltration membranes. It allows the direct observation of the behavior of water at the membrane surface during wetting and drying. For this purpose, an environmental scanning electron microscope (ESEM) was equipped with a special cooling stage, enabling the investigation of wet samples inside the microscope chamber. The images recorded from the membrane surfaces provide information about the number and size distribution of dry and wet pores during the drying process. Additional information about the wetting and drying of the membrane interior was gained by simultaneously measuring the temperature of both membrane surfaces as a function of time. The basic mechanism is the strong influence of the evaporation of cooled water from the membrane interior on the membrane surface temperature. These temperature characteristics reflect the interior membrane structure. The correlation between the microscopic parameters, obtained from the observation of the wetting and drying of the surface pores and the temperature characteristic, a macroscopic parameter, enables a qualitative description of the membrane structure. This information also allows the liquid and gas transport inside the complex membrane structure to be studied. In the present work two different types of flat microfiltration membranes were investigated.

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► Visualization of the wetting and drying process of the membrane surfaces.
► Accurate measuring of the membrane surface temperature changes during the processes.
► The surface temperature characteristic reflects the interior membrane structure.
► We were gaining the size distribution of the dry pores during the drying process.
► Correlation of the membrane mean pore size and the drying behavior.