Search

We report experimental results and a theoretical analysis of the Debye length in aqueous solutions of nonadsorbing polyelectrolytes. The measurements were done using a surface forces apparatus, in which the normal forces between smooth mica surfaces in aqueous hyaluronic acid (HA) solutions were measured as a function of surface separation (to ±1 A). HA is negatively charged and does not adsorb to the negatively charged surface of mica, as was established by optical and viscosity measurements and in agreement with the measured force−distance curves. From these measurements it appears that the multivalent polyelectrolyte is “depleted” from the gap between the surfaces. We use the mean-field Poisson−Boltzmann theory to theoretically predict the effective Debye length and double-layer force under such conditions and compare the predictions with the experimental results. The comparison gives excellent agreement and shows that the effective Debye length is determined solely by the monovalent ions in the soluti...

Freshly squeezed orange juice was ultrafiltered in a hollow fiber cross-flow ultrafiltration system. The suspended solids (pulp) in the juice were completely separated with a membrane cutoff of 5×10 5 molecular weight. The membrane retained most of the pectin material, and the viscosity of the permeate (juice serum) was appreciably reduced. Concentration of permeate by evaporation was achieved up to 75 o Brix. No pectinesterase activity was detected in the permeate. Some aroma compounds, particularly hydrocarbons, remained in the retentate