An apparatus for the study of macromolecular solutions by the Kerr effect

Solutions of macromolecules exhibit double refraction when subjected to an electric field (Kerr effect). A study of this effect may be made by applying a pulse of rectangular shape to such solutions. Measurement of the magnitude of the birefringence and of its rise and fall enables information on molecular parameters to be obtained and in particular values of molecular relaxation time. In this paper a detailed account is given of an apparatus suitable for making these measurements. The principles underlying the method and the design of the apparatus are presented. Linearly polarized light passes between the electrodes in a cell, through an analysing system on to a photoelectron multiplier, the output of which is displayed on a cathode-ray oscilloscope. The trace which appears when the rectangular field is applied to the electrodes is photographed and from it the necessary data are obtained. Two different methods of detection in which the output is proportional either to the double refraction δ or to δ 2 , respectively, are briefly discussed. The applied pulse has an amplitude variable up to 8 kV, and a duration of up to 2·5 μs with 10 to 90% rise and decay times of about 6 × 10 −8 s respectively. The apparatus is suitable for measuring molecular relaxation times in the range 10 −4 to 10 −8 s and this range may be extended by change of components. The method of calibration and the precision with which measurements may be made are described. Typical traces and results are shown.