he concepts of two concentrations

namely segmental and molecular concentrations for polymer blends has been proposed.The former is equivalent to the ordinary volume fraction and the latter is defined as the number of the chain heads in the unit volume for every polymer component.The entropy part of the Flory-Huggins free energy should be represented by the molecular concentration

and the mixing heat part should be represented by the segmental concentration.The two concentrations will be correlated each other by the conformational function of the said polymer chain. When neglecting the conformational fluctuation and ocnsidering only the influence of the molecular concentration fluctuation

the de Gennes scatte-ring function for polymer binary blends has been deducedon the basis of the gene-ral thermodynamical fluctuation theory.