Membrane formation at interfaces examined by analytical ultracentrifugation techniques

For the first time, the formation of polyelectrolyte complex membranes has been examined by applying analytical ultracentrifugation's synthetic bounda ry technique coupled with the twin scanning UV/vis and Rayleigh interferenc e optics. Systematic basic studies demonstrate the efficiency of the new me thod, as well as its advantages and limitations. In particular, various pha ses of the membrane formation process have been identified. These include i nitial membrane formation, membrane growth, membrane equilibration, and, in some cases, phase separation or dissolution. The technique presented herei n offers new and extended possibilities to study complex and/or structure f ormation by two components at interfaces dependent on polymer concentration , pH, ionic strength, and the component ratio. Temperature control, between 4 and 40 degreesC, allows precise studies to be carried out under physiolo gical conditions. Moreover, the membrane of defined thickness and structure and having an area of approximately 300 mm(2), can be recovered from the c ell for additional investigations. The polyanion sodium alginate and the po lycation chitosan were employed as a model system in this investigation. (C ) 2001 Elsevier Science B.V. All rights reserved.