Development of Structure in Hexadecyltrimethoxysilane Adsorbed on Silica

Abstract

The structural assemblies of hexadecyltrimethoxysilane (HDTMS) on silica particles were determined using temperature-modulated differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy (FTIR), and powder X-ray spectroscopy. At very small adsorbed amounts (<0.6 mg/m2), HDTMS molecules decomposed at a slightly higher temperature than bulk, exhibited symmetric and asymmetric FTIR resonances similar to those of liquid alkanes, showed a broad powder X-ray peak, and had a very small enthalpy of melting. These observations are consistent with poorly organized, disordered alkyl chains of directly attached molecules. At larger adsorbed amounts (>0.6 mg/m2 or more) in the “multilayer region”, the chains adopted more trans­(anti) conformations, their decomposition temperatures approached those of the bulk condensed HDTMS, and a sharper primary powder X-ray peak was observed. Also, both melting and crystallization enthalpies for the bound HDTMS were found to exponentially approach the bulk enthalpy. In particular, the enthalpy changes were fitted with a linear dependence for the “sub-monolayer” and then an exponential approach to bulk with an exponential constant of about 1.6 mg/m2. Together, these changes provide insight into how adsorbed HDTMS molecules underwent structural changes, from directly bonded on the surface to bulklike material.

Fabrication and Characterization of Hydrophobic Cellulose Nanofibrils/Silica Nanocomposites with Hexadecyltrimethoxysilane

“…Similarly, the HDTMS modification gives rise to inorganic/organic HDTMS, and the inorganic composition serves to improve the thermal stability as an insulator does. In particular, HDTMS-modified CNF/silica nanocomposites have decreased inorganic content (silica and inorganic HDTMS) compared to CNF/silica, but increased T 10 and T inf,1 , because organic HDTMS exhibits high thermal stability at a decomposition temperature from around 519 • C to 527 • C [60][61][62][63]. The HDTMS decomposed in a wide temperature range of ~200-500 °C, due to the relatively insufficient Si-O-Si crosslinking structure and the organic region of the hexadecyl group (-CH2(CH2)14CH3) [33,38,64,65].…”