Structural anisotropy of silica hydrogels prepared under magnetic field

TL;DR

This study demonstrates that silica hydrogels prepared under a magnetic field exhibit structural anisotropy, evidenced by birefringence and aligned crystal growth, marking the first such observation of birefringent silica hydrogels.

Contribution

The paper reports the first observation of birefringent silica hydrogels prepared under magnetic fields, revealing magnetic field-induced structural anisotropy.

Findings

Birefringence observed only at 5T magnetic field.

Aligned crystallite arrays formed in high magnetic field.

Narrower characteristic length distribution in birefringent samples.

Abstract

Birefringence measurements have been carried out on the Pb-doped silica hydrogels prepared under various magnetic fields up to 5T. The silica gels prepared at 5T were used as a medium of crystal growth of PbBr2, whose result implied the structural anisotropy; an aligned array of crystallites was obtained by transmission electron microscopy. While the samples prepared at 0, 1, and 3T have no birefringence, we found that the samples have negative birefringence on the order of magnitude 10^-6 as if the direction of the magnetic field is the optic axis of a uniaxal crystal. To the authors' knowledge, the birefringent silica hydrogels were obtained by gelation under magnetic field for the first time. Also, scanning microscopic light scattering experiments have been performed. The results indicate that the characteristic length distribution for birefringent samples is narrower than that for non-birefringent ones.