Apparatus for the Study of the Dielectric Properties of Macromolecular Solutions under Flow

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Abstract
Some solutions show a change in value of their dielectric constant and specific conductance when subjected to shearing stresses produced by a velocity gradient established within them. A detailed account is given of an apparatus which has been used for studying this effect. The solution to be investigated is placed in the annular space between two concentric cylinders. The gap between the cylinders varies from about 0.5 to 0.9 mm and has an average radius of about 9.8 mm. The outer cylinder can rotate at speeds up to 5000 rpm and, with aqueous solutions, gradients of the order of 3500 π sec−1 can be obtained without turbulence. Higher values are possible. The rotation is controlled by a Velodyne unit, which gives a continuously variable drive and, for any setting, gives a constant speed independent of load changes. Speeds are accurately determined by an electronic tachometer. The outer cylinder is of metal and the inner cylinder is made from an insulating material in which an electrode in the form of a narrow band is inserted. The metal cylinder and the electrode form a concentric cylinder capacitor or cell so that an electrical field can be applied in a direction perpendicular to the stream lines. The impedance of the cell filled with the solution under test can be determined over the frequency range 0.03 to 20 Mc using a Schering bridge and a twin‐T bridge for the low and high frequency ranges, respectively. A cooling system, controlled by thermostats, is provided to maintain the liquid at a constant temperature. The method of use of the apparatus is briefly described and the precision with which measurements may be made is fully discussed.

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