Sol-to-Gel and Gel-to-Glass Transitions in the As2S3-Amine system

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Abstract
It is proposed that solutions of arsenic trisulfide and ethylenediamine consist of arsenic-sulfur rings (As4S6) which are interlinked through sulfur-sulfur bridges. The Raman spectra of the solutions exhibit an intense band at 438 cm-1 which is attributed to the stretching resonances of these bridges. The bridges are not present in a-As2S3 glass, and thus, the intensity of the band has been used to characterize the molecular connectivity of sols and gels. This band is most intense in the highest viscosity gels, whereas the relative intensity of the band is diminished in the dry gels. The intensity of the band further decreases during vacuum heat-treatment of fibers drawn directly from the gel. TEM analysis of the fibers verify the creation of a dense amorphous structure, while SIMS depth profiles of the films further verify their composition. Altogether, these observations confirm the structural model proposed for the solution, and suggest a relaxation/ recombination process for the molecular gel-to-network glass transition.