Dynamic of Flexible and Large Macromolecules in Elongational Flow Using Flow Refringence
Several studies of the effect of a transverse shear stress on a macromolecular solution have been made by flow birefringence (F. B.) (e. g. (1)). For consequence of the unceasing rotation motion of the particles in this type of flow, the deformations of the flexible macromolecules remain generally small. But, in elongational flow and in the particular case where there is no rotational part, we can expect, in certain restrictive conditions, very strong molecular deformation such as the transition of the macromolecule from the coiled state to a streched form. Theoritical studies of this transition have been carried out (2–4), but there are only a few experiments comparable with proposed theories. The F.B. is a technique which lends itself perfectly to these studies. Localized flow birefringence (L.F.B.), appearing in experiments as thin luminous lines and showing the extention of the macromolecule in specific parts of the solution have first been observed with a system of opposed jets (5). But, in order to perform quantitative optical measurements, exploitable without ambiguity, we are limited to the use of two dimensional elongational flow. Such flows have already been realized in a system of two (6–9), four (10–11) or six rolls (12) and in the wake of an adequate obstacle in a uniform flow.
KeywordsTransverse Shear Stress Elongational Flow Coiled State Luminous Line Large Macromolecule
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