FORMATION OF OPTICALLY ANISOTROPIC ALGINIC ACID GELS UNDER DC ELECTRIC-FIELDS

It was found that optically anisotropic disk-shaped gels of alginic ac id were formed by a new gelation system which was based on the electro lysis 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 we re applied. The ion exchange and sodium ion transfer towards the catho de gave rise to formation of the alginic acid gel around the anode, co mbined with water transfer to the sol, i.e. dehydration, which was ass umed to originate from osmotic pressure induced by a one-sided distrib ution of the ionic solutes. In the case of the 0.6 wt% solution, almos t non-birefringent gels were formed and transformed to strongly birefr ingent 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% soluti on, only the latter types of gels were formed. With increasing voltage , the gels were largely deformed and the macroscopic anisotropy was mu ch disordered. It was revealed that the strongly birefringent gels wer e formed only when the alginic acid concentration was elevated above a critical value through dehydration. (C) 1998 Elsevier Science Ltd. Al l rights reserved.