Physical and chemical analysis of the polysaccharides isolated from Sargassum terrarium (brown algae) of Karachi coast showed characteristics of sodium alginate. The optical rotation and sulphated ash content were found to be - 113 degrees and 30.6% respectively. FTIR spectra showed a sharp and strong absorption hand at 1600 cm(-1) representing carboxylate ion, which confirms high uronic acid content of the product. Viscosity measurements revealed a linear relationship with increases in concentration and decreased with the rise in temperature of aqueous solution of sodium alginate. Thermodynamic parameters were determined by the change in viscosity data as a function of temperature and concentration. The free energy change of activation (Delta G eta) increased regularly as the concentration of sodium alginate increased, as well as rises in temperature. Higher values of free energy change of activation, showed the higher association of sodium alginate with water at a given temperature. The values of entropy change of activation (Delta S eta) of viscous flow also increased with the increase in concentration and temperature of sodium alginate solution. The high negative values of entropy change of activation (Delta S eta) showed that the solution of sodium alginate was more ordered in initial state than the activated one.
