Apparatus for Automatic Recording of Birefringence and Strain of Polymers

An equipment is constructed by which photo-viscoelastic effect of polymers can be studied easily and rapidly. A birefringence is obtained by the method of the Sénarmont's compensator. The light intensity is detected by a photomultiplier, RCA 931A, and the output is fed back to a servomotor with a tachogenerator. An analyzer is rotated by the servomotor, until the light intensity through a test piece becomes equal to a monitory light intensity which is radiated from the same source. The rotation of analyzer is transferred to a potentiometer which rotates by twice as much as that of analyzer. The birefringence is obtained as the voltage variation of potentiometer and a strain is measured by a differential transformer. They are continuously and simultaneously recorded on a same recording paper. A time constant of the birefringence detection is about 1/15 sec., and the strain of the test piece is measured up to 20%. Using a heating device, the measurements of the birefringence are possible in the temperature range up to 120°C. Interference filters and a composite quarter-wave-plate are used in the study of spectral dispersion. This equipment operates effectively in the study of photo-viscoelastic effects of the mixed polyesters.