Debye Length and Double-Layer Forces in Polyelectrolyte Solutions

Abstract

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 Å). 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 solution. Specifically, the effective Debye length κ eff -1 for the double-layer interaction is determined by an effective ionic concentration given by n s n c , where ns and nc are the bulk negative and positive monovalent ion concentrations, respectively.

Static Forces, Structure and Flow Properties of Complex Fluids in Highly Confined Geometries

“…16,31,52,77,86 A somewhat different behavior is found in polymer 24,50 and polyelectrolyte solutions. 13,14,24,44,75,76 Our experiments with low MW PEG 50 and hyaluronan or HA free in aqueous solution, 75,76 show that the polymer is extruded from between two negatively charged surfaces (of mica) upon confinement, i.e., it is pushed out from the gap and into the bulk liquid 'reservoir' surrounding the contact region. This should not be surprising: a negatively charged polyelectrolyte in solution (see the chemical structure of HA in the inset of Fig.…”

DNA duplex stabilization in crowded polyanion solutions

“…For our 12-mer DNA, PEG showed stabilization effect on DNA only when no NaCl was added. The stabilization effect of PEG disappeared even with just 100 25 mM NaCl ( Figure 3B). Such salt concentration dependent PEG stabilization effect has been explained previously.…”

“…[3][4][5][6] Apart from its practical importance in DNA replication, biosensor development and therapeutics, 7,8 DNA melting can be conveniently monitored using many spectroscopic techniques. The affinity of DNA strands can be precisely tuned by varying DNA length, sequence, and buffer 25 ionic strength. The melting temperature (Tm) of a DNA duplex is often increased by crowding agents since DNA (especially long DNA) melting is usually accompanied with an increase in the excluded volume.…”

“…Instead, we propose that modulation of electrostatic repulsion between DNA chains by 45 PAA should be an important reason. Such an electrostatic interaction cuased by concentrated negatively charged polymers has also been shown to condense long biological DNA, 14 to decrease double layer repulsion between negatively charged mica plates, 25 and to affect colloidal particle 50 stability.…”

Changes in pore morphology and fluid transport in compressed articular cartilage and the implications for joint lubrication

“…surfaces when pressed together under pressure would serve to provide the required low friction and wear protection even at high pressures and shear rates or sliding speeds (since for water films >1-2 nm thick the viscous forces are as for the bulk liquid, whose viscosity is particularly low [34,35]). A previous report that high molecular weight polysaccharides such as hyaluronic acid (HA) are excluded from such thin aqueous films due to the repulsion between the negatively charged HA and cartilage surfaces, further suggests the importance of 'weeping' lubrication in thin water films (although HA will provide good 'elastohydrodynamic' lubrication in thicker films [38][39][40]). …”