PROBE DIFFUSION IN POLYACRYLAMIDE GELS AS OBSERVED BY MEANS OF HOLOGRAPHIC RELAXATION METHODS - SEARCH FOR A UNIVERSAL EQUATION

Probe diffusion in Polyacrylamide (PA) gels was investigated with holographic relaxation methods. The probes were a benzospiropyran (SP) dye and bovine serum albumin labeled with p-(isothio-cyanato)azobenzene (BSA-ABITC). It was found that the reduced translational diffusion coefficients D/ D0 of probes in this gel system are well represented by the empirical stretched exponential equation, D/D0 = exp(-3.03/?h a69C0'94), where D and D0 are diffusion coefficients of the probe particle in the gel and in the pure solvent, respectively, Rh (À) is the hydrodynamic radius of the probe, and C (g/mL) is the PA concentration. The smaller probe (SP) diffused more slowly than the larger one (BSA-ABITC) at the gel concentration which gave the same ratio of probe radius fìh to mesh size ξ, where ξ (A) = 12.6C0,64 from dynamic light scattering. Literature values of D/D0 for D20, urea, and sucrose in PA gels are described by the same empirical equation. Reduced probe diffusion coefficients do not scale with single-variable Rh/i; but do scale approximately with the combination ñhC/£. No theoretical justification is currently available for the latter scaling parameter. © 1990, American Chemical Society. All rights reserved.