Asymmetric membranes characterization methods

Three new methods to characterize the pore structure and pore size distribution in the top layer of asymmetric membranes have been developed or refined in our laboratory during the past few years a) the gas ad-sorption/desorption method, b) thermoporometry and o) selective permeation (fractional rejection). 

The method of thermoporometry, developed by Brun, Lallemand, Quinson and Eyraud( ), represents another method applicable, at least in principle, to characterization of pore volume in ultrafiltration membranes (, ). However, for asymmetric membranes, pore volumes explored by thermoporometry may not be the volumes associated with membrane skins and "functional" pores. 

Smolders CA, Vugteveen E (1985) New characterization methods for asymmetric ultrafiltration membranes. In Lloyd DR (ed) Materials science of synthetic membranes. ACS Symposium Series 269. American Chemical Society, Washington, DC, p 327... 

We will start our discussion with the grafting to approach, which may be characterized as the simplest. Depending on the nature of the surface of the porous membrane that we want to decorate with a brush, we must choose an end-functionalized polymer chain (or a highly asymmetric block copolymer of an amphipathic nature) that may strongly adsorb from its functionalized part on the inner surface. Then in principle we may use the same method as for the case of a flat surface, i.e., dip the membrane in a solution that contains these polymers and then wait for the full formation of the brush. However, it has been shown [21] that self-assembly inside the pores is prohibited when the ratio of pore diameter to chain radius of gyration... 

Kong, J., and Li, K. (2001). An improved gas permeation method for characterizing and predicting the performance of microporous asymmetric hollow fiber membranes used in gas adsorption. J. 

At least two Raman spectroscopic methods are applicable in membrane surface characterization Fourier transform Raman spectroscopy (FT-Raman), and micro-Raman spectroscopy (Boccaccio et al., 2002 Gmger et al., 2001 Khulbe and Matsuura, 2000). In FT-Raman the sample molecules are excited with a near-infi ared (NIR) laser and appropriately configured Michelson interferometers, and Fomier transform processes are used in the collecting of scattered light and the analysis of the collected light. Almost the only requirement is that the sample to be analyzed with FT-Raman must not be black (Hendra, 2005). FT-Raman is a valuable tool in determining the overall chemical stmcture of a membrane, but it cannot characterize the asymmetric stmcture of a porous membrane matrix (Boccaccio et al., 2002). 

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