Evaluation of Responsibility for pH-responsive Glass by Surface Elemental Analysis

Approximately one hundred years have past since the discovery of the pH-responsive glasses. However, the reaction mechanism for pH-responsive glass has not been able to be clarified yet. In order to clarify the reaction mechanism, the elemental analysis of the surface of pH-responsive glass was carried out along the depth direction by secondary ion mass spectrometry (SIMS) and electron spectroscopy for chemical analysis (ESCA). In the results, the lithium concentration could be related with hydrogen concentration along the depth direction because lithium ions were replaced by hydrogen ions from the solution in the surface layer in the pH-responsive glass. Hence, the siloxy lithium group was changed into the silanol group through the exchange of lithium ions for hydrogen ions, and the replacement could be associated with the pH-response for the glass surface. The surface region, in which the replacement of lithium ions with hydrogen ions occurred, could be regard as the hydrated layer. The hydrated layer may provide the phase boundary for the pH-response. When the hydrated layer became smaller, the pH-response for the glass surface was more sensitive. Furthermore, the pH response was improved based on the present results.