Adriana Balan

Influence of hydrophobic characteristic of organo-modified precursor on wettability of silica film

The objective of this study is to design new hybrid silica materials as templates with hydrophobic properties, prepared at room temperature by a base catalyzed sol–gel process. As silica sources, organoalkoxysilanes functionalized with short hydrophobic chains were used: tetraethylorthosilicate (TEOS), methyltriethoxysilane (MTES), vinyltriethoxysilane (VTES), octyltriethoxysilane (OTES) and isobutyltriethoxysilane (iTES). It was shown that hydrophobicity of the functionalized silica nanoparticles increased as a function of length of the aliphatic chains (MTES < iTES < OTES) or when, instead of a hydrophobic alkyl chains (substituting group of silica precursors), a monounsaturated group was used (VTES). It was observed that the samples responded in a specific way to each type (hydrophilic or hydrophobic) of the dropped liquid. Even though the experiments were limited to short hydrocarbon chains, they showed that there is a threshold to reach high hydrophobicity of the hybrid surface.

Dental Enamel Quality and Black Tooth Stain: A New Approach and Explanation by using Raman and AFM Techniques

This contribution takes in account investigation of dental enamel regarding “quality” of hydroxyapatite material involved in the mineralization process. Areas damaged by black stain were investigated in order to evaluate changes in chemical composition as compared to those of healthy dental enamel. Different sectors on tooth surfaces were analyzed using micro-Raman spectroscopy. The integral areas of ν1 (960 cm−1) phosphate peak as well as of B-type carbonate peak ν2 (1070 cm−1) were obtained to investigate structural differences between the specimens (healthy/unhealthy enamel tooth and different sectors on unhealthy surface tooth). A complete list of chemical specimens involved in chemical processes on dental enamel surface was obtained by Energy Dispersive x-rays (EDX) investigation. It was noticed that mineralized carbonate peak at 1070 cm−1 decreased significantly for unhealthy tooth enamel or spots areas (as fluorite groups), suggesting that carbonate ions are easily dissolved in the presence of fluoride. The present study is confirming an organic origin for the dental “black stain.” The “black stain” is the result of a complex generation process from the damaged enamel, thus explaining their reappearance after the mechanical removing. A possible model for the “black stain” generation process is advanced.