Structural Arrangement of Hexadecyltrimethoxysilane on Diatomaceous Earth.

Nano-microscale morphologies of hexadecyltrimethoxysilane (HDTMS), an alkylsilane, adsorbed on diatomaceous earth (DE) were probed with temperature-modulated differential scanning calorimetry (TMDSC), thermogravimetric analysis (TGA), X-ray spectroscopy, and Fourier transform infrared spectroscopy. Initially, smaller amounts of HDTMS adsorbed resulted in a disorganized film with a decomposition temperature higher than that observed for bulk HDTMS due to the molecules being directly attached to the surface. FTIR and TMDSC results confirmed that at smaller adsorbed amounts, the molecules were largely amorphous and became more crystalline at larger adsorbed amounts. At very small adsorbed amounts, it was not possible to characterize the alkylsilane at submonolayer coverage, but at larger adsorbed amounts, it was found that the enthalpies measured increased exponentially, reaching the enthalpy value for the bulk HDTMS. The exponential growth scale was found to be around 1.5 mg HDTMS/m2 of DE surface, comparable to that found on fumed silica, in spite of the much smaller specific surface area and different morphology of DE. The understanding of the micro-nanomorphology is of significant relevance to the use of treated DE, especially in coatings.