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 ultracentrifugationʹs synthetic boundary technique coupled with the twin scanning UV/vis and Rayleigh interference optics. Systematic basic studies demonstrate the efficiency of the new method, as well as its advantages and limitations. In particular, various phases of the membrane formation process have been identified. These include initial membrane formation, membrane growth, membrane equilibration, and, in some cases, phase separation or dissolution. The technique presented herein offers new and extended possibilities to study complex and/or structure formation by two components at interfaces dependent on polymer concentration, pH, ionic strength, and the component ratio. Temperature control, between 4 and 40°C, allows precise studies to be carried out under physiological conditions. Moreover, the membrane of defined thickness and structure and having an area of approximately 300 mm2, can be recovered from the cell for additional investigations. The polyanion sodium alginate and the polycation chitosan were employed as a model system in this investigation.