Viscous Fingering

Based on previous discussion at section 2.2.3.2, the widely phenomenon known as viscous fingering phenomenon which proposed by previous studies [8, 9] have been used in the explanation of ceramic membrane fabricated via phase inversion technique. So far, there are two types of structure could be obtained from this technique: finger-like and sponge-like structure. In order to characterize this unique features of viscous fingering mechanism, a futher study have been investigated by Wang and Lai with applying different types of non-solvent coagulant bath during immersion precipitation [10]. In this study, the same experimental test was applied by using distilled water, ethanol and mixture of 70% NMP and 30% water. Interestingly, by adapting previous

Interestingly, by controlling these parameters, the membrane structure could also be controlled. Many studies have been conducted in investigating the effect of different non-solvent coagulant bath in membrane fabrication via phase inversion system. Wang and Lai demonstrated that viscous fingering is responsible for the formation of finger-like voids in the phase inversion of ceramic membrane fabrication [10]. In the study, flat-sheet alumina membranes was used as a benchmark to verify the unique features of this viscous fingering phenomenon by using three different types of coagulant bath; distilled water, ethanol and mixture of NMP and water. Among these different cogulants, water is the strongest while mixture of NMP and water is the weakest. Commonly, NMP was added into water as the coagulant bath is to slow down the precipitation rate during phase inversion (consolidation process). The order of coagulant in the study from strong to weak is water > ethanol > mixture of 70% NMP and 30% water. In addition, the study revealed the finger-like structure could be obtained by membrane immersed into distilled water. Figure 2.14 shows cross sectional SEM images of PVDF of hollow fibre membrane fabricated at different concentration of ethanol added into water bath. The decreased finger-like voids structure obtained are effect from the increased of ethanol content. This is in correlation of precipitation rate decreased due to the addition of