Carbon—Silica Dual Phase Filler: Part IV. Surface Chemistry

Abstract

Abstract A method for estimating the amount of functional groups on the carbon—silica dual phase fillers (CSDPF) available to react with organosilane coupling agents is reported. The method employs trimethylchlorosilane (TMCS) as an analytical probe, and involves equilibrating the samples with TMCS in toluene. The amount of TMCS that reacts with the surface functional groups is obtained by monitoring the concentration of reactants and products of the reaction by Gas Chromatography Mass Spectrometry. The amount of TMCS reacted with the fillers' surface functional groups is compared to the pH, and the active hydrogen content as measured by LiAlH4. Comparison of these measures with the CSDPF, carbon blacks and a fumed silica sample is provided. The dual phase fillers have a heterogeneous surface, containing both carbon and silica phases. Multipoint BET nitrogen surface area is used in combination with iodine number to estimate the individual carbon and silica phase surface areas. From this, the packing density of the trimethylsilyl group attached to the silica phase of the CSDPF surface was estimated and compared to silica. Silanols on these dual phase fillers were detected by infrared spectroscopy. The infrared band for silanols is located at 975 cm−1. The absorbance of this band is shown to correlate with TMCS uptake and diminish after reaction with TMCS, suggesting that silanols indeed are participating in the uptake of TMCS.