Survey of Experimental Results

As may be clear from the title of this monograph, the flow birefringence of polymer melts will be treated in the general context of the rheology of these fluid systems. As a matter of fact, it does not seem desirable to treat the flow birefringence technique as an independent method by which polymeric fluids can be characterized. For such a purpose the flow birefringence method suffers too much from a number of shortcomings. First of all, only clear fluids can be investigated. This means that systems containing filler particles must be excluded from the investigation. (Fortunately, pure crystalline polymers which are opaque at room temperature as a consequence of the microcrystalline structure, become clear above their melting points.) Another drawback of this method is that it is indirect. Rheologists are interested in the interrelations between stresses and strains: rheology is part of mechanics and not of optics.