Spectrofluorimetric studies of lithium conducting silica gels with LiNO3, LiCl or LiBr

Changes of the relative water content of the pore liquid in lithium conduct ing silica sol/gel monoliths were studied. The initial composition of the s ols was TMOS:H2O:HCl:LiX:MeOH:HPS = 1: 20:5 x 10(-4):0.2:3:10(-5) (LiX = Li NO3, LiCl or LiBr). The measurements were made by spectrofluorimetry with p yranine as a photoprobe. Initial changes of water content are due to the hy drolysis of TMOS molecules. Low rates of condensation lead to an almost con stant level of water content over long periods of time, following the hydro lysis. Pin-holing of the Parafilm seals produces faster changes of water co ntent. These changes are ascribed to the effect of preferential methanol ev aporation and entrapment of some liquid inside closed or very narrow pores of the gels. (C) 1999 Elsevier Science B.V. All rights reserved.