Transient electric birefringence of macromolecular systems

Abstract

The transient electric birefringence method, i. e. the transient Kerr effect, has been employed to study the optical, electrical and geometrical properties of three macromolecular systems. An apparatus is described in which the birefringence could be measured when d. c. electric field pulses (of duration 1μs to 5s and strength up to 50 KV/cm) and a. c. electric field pulses (of duration greater than 5 ms, of frequency up to 20 kHz, and strength up to 3 KV/Cm) were applied to solutions of macromolecules.

Both the linear and quadratic optical systems have been employed to measure the induced birefringence. A theoretical analysis and review of the errors implicit in such measurements is given, with suggested alignment and calibration procedures.

For the first time in electro-optic work, a data-logging system and computer program have been developed and employed, and enabled the automatic recording of transient responses with subsequent high speed data analysis.

Measurements have been made on a polypeptide poly – β – benzyl – 1 – aspartate in two solvents. These show how the method can be used to study a rigid macromolecule.

A novel investigation was made on the interaction of an anionic surfactant, sodium dodecyl sulphate, with a flexible polymer, polyvinylpyrrolidone. The large variation of Kerr constant observed with addition of surfactant indicated a great potential use of this method for studying polymer surfactant interactions.

An aqueous suspension of the bacteria E. coli was also studied, but changes in turbidity and not birefringence were the origin of the observed effects. Novel practical methods of investigation, and turbidity calculations carried out with the aid of a computer enabled size parameters and electrical properties to be determined for E. coli. For the first time such results were in agreement with electro-optic light scattering measurements.