Layer shrinkage membranes

A last complication results from the measurement of the thickness of supported layers. This can easily be done with SEM for calcined layers. Wet lyogel, or even dry xerogel, layers cannot be measured in this way. Reproducible thickness measurements on wet lyogel films could not be obtained with other easy-to-perform methods. Consequently layer thicknesses were measured after calcination. Estimates of the shrinkage in the thickness direction were made for supported alumina (boehmite) membranes dried at 40°C and 60% RH made with a standard precursor solution of 1 mol AlOOH/1 stabilised at pH = 4 by... 

One of the main instabihties of multiple emulsions is the osmotic flow of water from the internal to the external phase, or vice versa, which leads to shrinkage or sweUing of the internal water droplets, respectively. This process assumes the oil layer to act as a semi-permeable membrane (permeable to water, but not to solute). 

Fig. 6.7 Linear shrinkages of the dense layer and the porous support (lefi) and photograph of the resulting co-smtered asymmetric membrane (right)...

Visualization with invasive methods in membrane apphcation requires removing the membrane from its module. Losses, shrinkages and disturbances of the sample materials are likely to occur during the sample preparations and pose particular challenges for MBR applications. Each technique is discussed here for its potential to visualize and characterize the fouling layer in MBR applications. 

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