Water oxygen-17 magnetic relaxation in polyelectrolyte solutions

Abstract

Water oxygen-17 longitudinal and transverse relaxation rates have been measured at two frequencies for aqueous solutions of poly(acrylic acid) and poly(methacrylic acid) under conditions of variable temperature, concentration and degree of dissociation. The proton-exchange broadening of the ¹⁷O resonance from these polyacid solutions has also been investigated. The data show that the residence time for water molecules interacting with the polyacid is of the order of 10^–8 s, during which time they reorient anisotropically, an order of magnitude slower than bulk water, and engage in rapid proton transfer with acidic groups. The motional perturbation of associated water is to a large extent electrostatically induced. A new method for determining an upper limit for the lifetime of ‘bound’ water from the proton-exchange broadening is employed and the necessary equations are derived.