Bis(trimethylsilyl)carbodiimide was synthesized according to the literature [14]. THF and toluene were dried by refluxing with sodium. The synthesis of silicon carbodiimide sols or gels was performed under argon using standard Schlenk techniques. Pyridine (100Β±500 mL), bis(trimethylsilyl)carbodiimide (1Β±10 mL), and distilled tetrachlorosilane (1Β±10 mL) were mixed. Different molar ratios of tetrachlorosilane/bis(trimethylsilyl)carbodiimide were used (T/B = 1:1, 1:2, 1:4). After aging the mixture at room temperature, the clear solutions turned to opalescent colloidal solutions or a white or yellow gel within several hours to one month, depending on the molar amount of the reagents and the catalyst.
SEM was performed on a Philips XL 30 FE9 microscope. Specimens were prepared by dipping the carbodiimide sol on a carbon film followed by drying in vacuum at room temperature for 2 h. The dried samples were observed directly or after being sputtered with a thin gold layer. All these procedures were performed under inert gas in order to prevent hydrolysis.
The particle size distribution was measured by PCS using a Malvern Zethasizer 3000 (England). The as-synthesized and aged colloidal solution was filled into a cylindrical quartz container under argon and measured without dilution.
Nitrogen adsorption isotherms were determined on an Autosorb-3B, Quantachrome Corp., Quantachrome Autosorb, automated gas sorption system (USA), and analyzed using the BET model. Powder samples of 120 mg were obtained by drying colloidal solutions at 100 C under vacuum and filled into glass capillaries under argon. The sample was further treated by evacuation for 5 h at 100 C prior to the measurement.
FTIR spectra were recorded on a PerkinΒ±Elmer FTIR 1750 spectrometer. Samples were prepared by pressing the mixture of the silicon carbodiimide powders (1 wt.-%) and KBr into a small pellet in a glove box (M Braun, 150G-1SPS, H 2 O and O < 1 ppm). Chemical analysis was carried out at the Microanalytisches Labor Pascher, D-53424 Remagen (Germany).