Development of Polymer Molecule Manipulation by Means of Flow Field and Its Application to Polymer Dynamics

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It has been well established that flexible polymers manifest a conformational transition in a well-defined elongational flow field : a coil stretch transition (CST). We investigated the CST of polymers under various conditions and tried to manipulate a polymer molecule by stretching in the elongational flow field. The elongational flow field was generated by a four-roller mill system where the response of the polymer molecule to the elongational field was monitored by a flow birefringence.(1) Coil-globule transition of a T4 phage DNA molecule was investigated by means of the elongational flow field birefringence method in conjunction with a fluorescent micrograph method. A random coil is expected to be elongated by the flow field and generate birefringence signal while a globular molecule is considered not deformed and there should be no birefringence. The expectation was empirically revealed to be the case. A birefringent globular molecule was discovered by a comparison of the birefringence data with that of fluorescent micrograph. Such a birefringent globular molecule was found to be in the shape of an ellipsoid with an optical anisotropy by the stopped flow experiment using the four-roller mill system.(2) A polyelectrolyte changes its flexibility with the salt concentration in the solution. The flexibility change of the polyelectrolyte was quantified by the CST observation in the elongational flow. By changing NaC1 concentration of the aqueous DNA solution, the CST at each NaC1 concentration was observed. A critical strain rate where CST occurs increased linearly with NaC1 concentration. These facts indicate that the DNA molecule was electrically neutralized by Na^+ ions gradually and simultaneously whole through the molecule.The regulation of the conformational transition by the elongational flow field was not realized because of the limit of the strain rate generated by the present flow generator. By improving the apparatus, we will retry the experiment.