Interactions between inorganic salts and polyacrylamide in aqueous solutions and gels

Abstract

The swelling of poly(acrylamide) (PAAm) gels and the osmotic pressure of linear PAAm in aqueous solutions were predominantly affected by anion type and increased according to the lyotropic series ranking of sodium halide anions: F− < (H2O) < Cl− < Br− < I−. The osmotic pressure of PAAm in all examined salt solutions followed the scaling theory, with an exponent of 2.3 ± 0.1. In solutions of a sodium halide series, the value of the pre‐exponential factor seemed to depend on salt concentration, anion radius, and the apparent “anionic‐portion radius” of the water molecule. This radius, extracted from the literature data, marks a transition point of the anion radius effect. Larger anions increase the osmotic pressure of PAAm more significantly as their concentration increases and vice versa. The effects of the anions on the osmotic pressure of PAAm are related to their preferential interactions with the polymer. Iodide, which increased the osmotic pressure of PAAm with respect to its value in pure water, seemed to preferentially adsorb onto the polymer with a binding constant of Kb = 9.7 ± 2.0 M−1 determined by isothermal titration microcalorimetry. However, fluoride, which decreased the osmotic pressure, was preferentially repulsed. The mechanisms of attraction and repulsion were attributed to ion‐water‐polymer interactions and the solvent quality of the hydrated ions. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 508–519, 2003

Interactions of glucose and polyacrylamide in solutions and gels

“…These methods were described previously for the swelling of two types of systems: macroscopic gels7 and microscopic gel beads 8…”

“…These were determined according to methods described previously 7, 8. Briefly, PAAm solutions of known polymer and glucose concentrations were accurately weighed in 50‐mL Amicon stirred ultrafiltration cells (model 8050) with 10‐kD‐MWCO Amicon‐Millipore YM‐10 regenerated cellulose membranes.…”

“…Testing for glucose binding was performed as previously described7 for salts. In brief, binding thermodynamics were studied with a MicroCal VP‐ITC instrument as follows.…”

Spoliation of fluoroperm rigid gas permeable contact lens by sodium chloride: A positron annihilation study

“…Supporting evidence to this proposition can be found in the literature. 39 The following mechanism may be in place to explain the effect of ions of sodium chloride on the structure of water and the resulting increase in osmotic pressure. Several studies in the past suggest that ions directly interact with macromolecules by binding to their hydrophilic groups, 40 and few other studies suggest that indirect interaction is also possible with the polymer through perturbation of the water environment or by induction of changes in hydrogen bonding of water to the polar groups of the polymers.…”

“…39,43 This results in the reduced chemical potential of water, in overlapping excess zones of adjacent polymer chains; thereby a water potential gradient is established which serves as a driving force for water diffusion into these overlap zones, i.e., increased rate of water diffusion occurs. In effect, sodium chloride salt adsorbs to the contact lens polymer chains, releasing the bound water molecules, thus increasing the free water (bulk water) content in the lens.…”