Polydiacetylenes, birefringence

IV. Electric Field Induced Birefringence of Polydiacetylene 4BCMU A. Theoretical Background (see ref. 5)... 

Figure 6. Transient response of the birefringence of polydiacetylene 4BCMU for a chopped ac electric field with applied rms field strength of 900 V/cm (lower curve) and 1400 V/cm (upper curve), showing the build-up and decay of orientational order.

This slow mode can be excited and detected in polydiactylene gels through the interaction of a low-frequency ac electric field with the anisotropic polarizability of rod-like polydiacetylene macromolecules. The specific coupling of the ac field excitation and the birefringence detection to the network allows direct measurements of the fraction of the sample for which there is an elastic restoring force (the "infinite cluster"). 

Figure 10. Resonant birefringence detection of slow elastic modes in a gel of O.S wt% polydiacetylene in toluene.

K. C. Lim, A, Kapitulnik, R. Zacher, and A. J. Heeger, Conformation of polydiacetylene macromolecules in solution field induced birefringence and rotational diffusion constant, J. Chem. Phvs. 52 516... 

There are two kinds of electric birefringence techniques, the FEBS and the transient electric birefringence (TEB) method [171, 173]. The TEB method was applied to the solution of polydiacetylene to investigate the rod-coil conformational transition of the polymer chains [174]. The FEBS, on the other hand, has the advantage of giving us the mobility of the carriers along the polymer chain separately from the hydrodynamic radius of the polymer chain (usually referred to as the polymer conformation) [149]. Shimomura et al. [175] have recently applied the FEBS technique to the solutions of dilutely doped PHT to study the intrachain conduction in the conducting polymer and its relation to the main-chain conformation. 

Quadratic Kerr effect has been mainly studied in polydiacetylene solutions and gels (Kapitulnik et al.(1984), Lim and Heeger (1985) Lim et al. (1985) Kapitulnik et al. (1986)). Strong electric birefringence was observed with large rotational diffusion constants (t 0.1 -r 0.2 s), characteristic for very long molecules. 

Conformation of Polydiacetylene Macromolecules in Solution" Field Induced Birefringence and Botational Diffusion Constant", J. Chem. Phys., 82, 516-521. 

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