Spectral broadening of light scattered from alginate gels

Abstract

AbstractLight scattering Rayleigh linewidth measurements have been made on calcium alginate gels using the autocorrelation method. The degree of broadening has been found to be small (∼2%) although two relaxation times (∼7 and 50 msec) within the broadened component have been measured. Oscillations were generally found to be superimposed upon the autocorrelation function and these have been positively identified with bulk oscillations of the specimen. By scanning through the gel with the focused laser beam it has been shown that there are long range (tenths of millimeters), long term (tens of minutes), fluctuations in alginate density.Experiments were also carried out in which the diffusion constants of dextran fractions and globular proteins within the gel were measured by investigating the heterodyne beat spectrum. It was found that the movement of macromolecules with hydrodynamic diameters less than 10 nm was virtually unimpeded by the gel. Diffusion constants fell to about one third of those in aqueous solution for hydrodynamic diameters of ∼30 nm.