Magnetic field effects on sol-gel phase changes in aqueous polymers

Magnetic field effects were studied on the temperature-induced phase change for the sol-gel systems including the natural high polymer agarose or methyl cellulose. Aqueous agarose and methyl cellulose were set to gel on cooling and heating, respectively. The gel melting temperature T-m was observed after the gels were formed under the influence of magnetic fields up 5 T. The magnetic field exposure resulted in 1.0 K rise in T-m for agarose gels and 3.5 K lowering in T-m for methyl cellulose gels. The magnetic effects became remarkable with the decrease of polymer concentration. The changes in melting temperature saturated at about 3 T. The birefringence for the 0.5 wt.% agarose gels which were formed in different magnetic fields increased with increasing magnetic field but saturated at about 3 T. The exposure of magnetic fields causes the alignment of the polymers and leads to a stable structure of the gels. (C) 1998 Elsevier Science B.V. All rights reserved.