Birefringence of silica hydrogels prepared under high magnetic fields reinvestigated

TL;DR

This study investigates the birefringence of Pb(II)-doped silica hydrogels prepared under high magnetic fields, revealing diverse birefringence behaviors and their relation to magnetic field strength, challenging previous assumptions about diamagnetic silica.

Contribution

Reinvestigated silica hydrogel birefringence under magnetic fields using quartz cells, discovering multiple birefringence classes and proportionality with magnetic field strength.

Findings

Identified four classes of birefringence: positive, negative, and none.

Found proportionality between birefringence and magnetic field strength for positive classes.

Revised previous conclusions about birefringence direction and magnitude.

Abstract

Birefringence is an indicator of structural anisotropy of materials. We measured the birefringence of Pb(II)-doped silica hydrogels prepared under a high magnetic field of various strengths. Because the silica is diamagnetic, one does not expect the structural anisotropy induced by a magnetic field. In previous work [Mori A, Kaito T, Furukawa H 2008 Mater. Lett. 62 3459-3461], we prepared samples in cylindrical cells made of borosilicate glass and obtained a preliminary result indicating a negative birefringence for samples prepared at 5T with the direction of the magnetic field being the optic axis. We have measured the birefringence of Pn(II)-doped silica hydrogels prepared in square cross-sectional cells made of quartz and reverted the previous conclusion. Interestingly, the magnetic-influenced silica hydrogels measured have been classified into four classes: two positive birefringent ones, no birefringent one, and negative birefringent one. Proportionality between birefringence and the strength of magnetic field is seen for the former two.