Comparison of Transmission and Diffuse Reflectance Sampling Techniques for FT-IR Spectrometry of Silane-Modified Silica Gel

Two sampling techniques are compared to study the effect of silylation reaction conditions on the extent of methoxy group hydrolysis of trimethoxymethylsilane (TMMS) on the Cab-O-Sil surface. When a pressed pellet of TMMS-modified Cab-O-Sil is used for transmission studies, the methoxy groups hydrolyze rapidly while the same sample studied by diffuse reflectance is stable toward hydrolysis for at least 60 min. The release of water from the silica gel pores when the sample is pressed is believed to be the reason for the rapid hydrolysis. To avoid undesirable hydrolysis of the silane, the diffuse reflectance sampling technique is preferred.