| Abstract
| - We report experimental results and a theoretical analysis of the Debye length in aqueoussolutions 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) solutionswere measured as a function of surface separation (to ±1 Å). HA is negatively charged and does notadsorb to the negatively charged surface of mica, as was established by optical and viscosity measurementsand in agreement with the measured force−distance curves. From these measurements it appears thatthe multivalent polyelectrolyte is “depleted” from the gap between the surfaces. We use the mean-fieldPoisson−Boltzmann theory to theoretically predict the effective Debye length and double-layer force undersuch conditions and compare the predictions with the experimental results. The comparison gives excellentagreement and shows that the effective Debye length is determined solely by the monovalent ions in thesolution. Specifically, the effective Debye length κeff-1 for the double-layer interaction is determined byan effective ionic concentration given by, where ns and nc are the bulk negative and positivemonovalent ion concentrations, respectively.
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