Failure of the scalar field description

The collective coordinate formalism given in Section 5.5.1 is not capable of describing the whole aspect of polymer dynamics. For example, the quantities which are related to the orientation of the bond vector dRJdn, such as stress, birefringence, and electric displacement, are not expressed by (Cft(f), and therefore cannot be dealt with in this framework. This is in contrast to the critical dynamics of binary solutions in which the dynamics is entirely q ecified by an equation of motion for the concentration fluctuation. To discuss the orientation dynamics of polymers, other collective coordinates are needed. A possible collective coordinate is  

However, the usefulness of such coordinates has not yet been fully worked out. 

An alternative idea proposed by Edwards and Freed is to consider the motion of a single chain in an effective medium which includes the effect of the other chains. The property of the effective medium is determined self-consistently from the single chain dynamics. Though this method fails to describe the entanglement effect appropriately, it indicates an important aspect of the hydrodynamic interaction in the concentrated system, which is the screening of the hydrodynamic interaction. 

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