Effect of alkyl chain length on surface silanization of silica

Abstract

The effect of the chain length of n-alkyldimethylchlorosilane on surface silanization was extensively studied. The alkyl surface concentration for primary and endcapping silanization were determined using a more accurate gravimetric method instead of the conventional carbon analysis, and the residual hydroxyl groups were detected by a modified Sears' titration method. It was found that there was a linear relationship between the alkyl surface concentration and the number of carbon atoms in the chain of the silane for the primary bonding. It was also found that the total alkyl surface concentration after endcapping remained the same irrespective of the different silanes employed in the primary bonding. It was confirmed that the sum of total alkyl concentration and residual hydroxyl surface concentration equaled the original hydroxyl surface concentration for low-temperature silanization. Compared with previous data, the present study revealed that micropores would consirably decrease the alkyl concentration for long-chain silanes. A size-exclusion mechanism is proposed, tentatively, to interpret the chain-length effect on silanization.