Field of Expertise: Advanced Material Science
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Field of Expertise: Advanced Material Science | |
In-Situ Wetting Investigations of Microfiltration Membranes in the ESEM Polymeric microfiltration membranes are used in various fields of applications. They got installed for the separation of colloids and particles e.g. in medicine, science and water treatment. For future membrane developments and improvements, a better understanding of the inner microstructure and the interaction between the membrane walls and the applied fluid is necessary. Many of the common techniques for characterization of the membrane construction and its behavior are based on either the measurement of macroscopic parameters or on statistical methods, like simulations and measurements established on 3D-reconstructed models. The latter often do not provide fundamental insight in the interaction between the hydrophilic or hydrophobic membrane and the fluid. Therefore a new method was invented to investigate a representative volume, measure both microscopic and macroscopic parameters and to correlate them. A special experimental setup, which fits into the specimen chamber on an environmental scanning electron microscope (ESEM) and enables the investigation of wetting and drying of membranes was designed and manufactured. The possibility to also record images of wet specimens makes the ESEM perfect for study of physical/chemical processes on the microscale. Even the wetting and drying of just one specific pore can be observed. Moreover a polymeric membrane consists often of several different asymmetric arranged layers: the mostly thin separation layer and the supporting or backup layers. For the macroscopic scale investigation the temperatures at the two membrane surfaces were recorded during the wetting- and drying process. Because of the variation of the layer setup (thickness and position) in different membrane types, each type has its own kind of temperature profile. This profile discloses us more details about the inner structure and its behavior in real conditions. Fouling of a layer should cause change in the temperature profile. Additional procedures like sealing of one membrane side or modifying the wetting and drying parameters, also helps to improve the structure determination. For future research this new method gives us the possibility to also investigate used membranes to get additional information on the ageing process. E.g. most probably it will be possible to find out in what layer the biggest damage happened during usage and of which kind this damage is. |