Novel ringing silica gels that do not shrink

Silica gels usually show the phenomena of syneresis. ne gels shrink with time after preparation, This process is also observed with the gels that are prepared with the new Si precursor silicic acid tetrakis(2-hydroxyethyl) ester. It is shown that the shrinkage of the gels can be prevented if the cationic precursor N-[(trimethoxysilyl)proyl]-N,N,N-trimethylammonium chloride is added. The gelation process and the final structure of the gels were observed by rheological and SANS measurements. The gelation time is increasing with the concentration of the cationic precursor. After mechanical stimulation the gels are ringing in audible frequencies. This effect is explained by the high value of the storage modulus G' of the gets and the ratio of G' over G" (loss modulus). Increasing cationic precursor concentrations lower the audible frequencies. The wet silica gels were supercritically dried by CO2 and characterized by FE-SEM and BET-measurements. From the surface area the radius of the SiO2-particles was calculated and was in the range between 9.5 and 12.3 nm.