IMPEDANCE STUDIES OF THE EFFECTS OF SOLVENT CHEMISTRY AND SOLVENT EXCHANGE ON AGED GELS

Sols were prepared in the systems TMOS:H2O:Solvent:HCl with molar rati os of 1:4:Y:0.0005 with Y=3 for Solvent=MeOH, EtOH, DMF and Y=0.75 for Solvent=DMSO, The sols were cast into cuvettes and covered with paraf ilm during gelation and aging. The conductivity of the sols and gels i nside the cuvette was determined by impedance spectroscopy, The conduc tivity of the gels was obtained in a special holder outside of the cuv ette. Solvent exchange experiments were carried out three times with a n excess of MeOH, EtOH, DMF and DMSO as exchange solvent. The conducti vity of the exchange solvent was monitored in a conductivity cell and that of the exchanged sample in the holder. Evidence is presented that only a certain portion of the protons contribute to the conduction in the as-prepared samples of gel. The exchange experiments can be inter preted by the combination of two factors, namely a different proton co ncentration inside and outside of the gel at the end of exchange and a n additional conduction process which does not involve protons, (C) 19 97 Elsevier Science S,A.