According to the ideal necklace model for the linear macromolecule, as introduced by Rouse, the macromolecule and its segments expand to infinite length if subjected to larger and larger shear stress. A more realistic model has to take into account that the segment has a finite maximum lengthbinfin;which cannot be exceeded even at largest stress. Therefore, the elastic restoring forces transmitted by the segment and acting on the ends of the segment have to be assumed to increase more than linearly with the distanceband to become infinitely large atbinfin;, yielding a modification of the eigenvalues of the corresponding restoringhyphen;force matrix. The eigenfunctions are considered to be the same as in the original Rouse model. With the new set of eigenvalues the segment deformation of the linear molecule in laminar flow is claculated as a function of the flow parameter bgr;. Saturation effects show up which are missing in the original model. The results obtained are formally identical with those of the original Rouse model if bgr; is replaced by a modified bgr;*=bgr;/(E0*+frac12;R).E0*is the nonlinearity factor of restoring force in solution at rest depending on thebinfin;/b0ratio, andRis the maximum increase of this factor taking place in the central segment of the model and depending on bgr;. Intrinsic viscosity and birefringence extinction angle are calculated for somebinfin;/b0ratios and compared with the corresponding values of the dumbbell model.
展开▼
