POSITRON-ANNIHILATION LIFETIME STUDIES OF FREE-VOLUME IN OVALBUMIN GELS

The dependence upon concentration of sodium chloride of free volume in ovalbumin gels, a main component of an egg white, is studied by the p ositron annihilation lifetime technique. The average free-volume radiu s in ovalbumin gels was about 0.27 nm at 298 K, smaller than those of organic polymers such as low-density polyethylene (0.34 nm at 300 K) a nd polystyrene (0.29 nm at 300 K). These differences suggest that the positronium annihilates in free volumes located close to hydrogen bond s, thus decreasing average free-volume radius. Free-volume content dec reased with the increase of NaCl concentration up to 30 mM. At lower c oncentrations of NaCl, it seems that a correlation exists between micr oscopic free volume and macroscopic hardness of the ovalbumin.