Carbon-silica dual phase filler: Part IV. Surface chemistry

A method for estimating the amount of functional groups on the carbon-silic a dual phase fillers (CSDPF) available tu react with organosilane coupling agents is reported. The method employs trimethylchlorosilane (TMCS) as an a nalytical probe, and involves equilibrating the samples with TMCS in toluen e. The amount of TMCS that reacts with the surface functional groups is obt ained by monitoring the concentration of reactants and products of the reac tion by Gas Chromatography Mass Spectrometry. The amount of TMCS reacted wi th the fillers' surface functional groups is compared to the pH, and the ac tive hydrogen content as measured by LiAlH4. Comparison of these measures w ith 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 combina tion with iodine number to estimate the individual carbon and silica phase surface areas. From this, thr packing density of the trimethylsilyl group a ttached 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 o f this band is shown to correlate with TMCS uptake and diminish after react ion with TMCS, suggesting that silanols indeed are participating in the upt ake of TMCS.