Formation of optically anisotropic alginic acid gels under dc electric fields

It was found that optically anisotropic disk-shaped gels of alginic acid were formed by a new gelation system which was based on the electrolysis of water. In this system, electrodes composed of a central anode and a surrounding cathode of 30 mm radius were dipped in 0.6-2.6 wt% sodium alginate solutions, and d.c. electric fields of 1.7-6.7 V/cm were applied. The ion exchange and sodium ion transfer towards the cathode gave rise to formation of the alginic acid gel around the anode, combined with water transfer to the sol, i.e. dehydration, which was assumed to originate from osmotic pressure induced by a one-sided distribution of the ionic solutes. In the case of the 0.6 wt% solution, almost non-birefringent gels were formed and transformed to strongly birefringent gels, where the chains were deduced to be oriented parallel to the side surface of the gels. In the case of the 1.3 or 2.6 wt% solution, only the latter types of gels were formed. With increasing voltage, the gels were largely deformed and the macroscopic anisotropy was much disordered. It was revealed that the strongly birefringent gels were formed only when the alginic acid concentration was elevated above a critical value through dehydration.