REFRACTOMETRIC MEASUREMENT OF POLARIZED LAYER STRUCTURE - STUDIES OF HYALURONIC-ACID ULTRAFILTRATION

In order to gain insight into the concentration polarization process, we have constructed a novel ultrafiltration cell and experimental system which allows direct, non-invasive, real time measurement of polarized layer structure. The device employs a differential refractometric method of polymer detection, and consists essentially of a laser beam passing through (in order): the polarized layer, an angled glass interface, and a reference solution. The deflection of the emerging laser beam is sensed and can be directly related to the polymer concentration at measurement locations upstream of the membrane. The apparatus can resolve polymer concentrations as low as 60-70 ppm; however, spatially resolving profiles within 200-mu-m of the membrane face is problematic. We have used this system, in addition to the more conventional measurements of total polarized layer resistance, to carry out preliminary studies of the ultrafiltration of the random coiling polyelectrolyte hyaluronic acid. Quasi-steady and transient concentration profiles are presented and compared with theory. Discrepancies between theory and experiment, possibly due to membrane fouling, were observed. We conclude that the differential refractometric approach is a potentially valuable tool for studying polymer ultrafiltration and the physicochemical behaviour of polymer solutions.