Self-assembly of organic-inorganic hybrid nanolayers: effect of endgroup polarity on nanostructures

Molecular self-assembly (MSA) offers a convenient way to elaborate highly ordered and lightweight nanostructures with molecular-level control of material structure, composition, and dimensions. This sub-branch of supramolecular chemistry which focuses on the spontaneous and reversible construction of ordered aggregates through weak intermolecular interactions represents a facile route to produce organic-inorganic hybrid nanolayers with long-range ordering. Over the past twenty years, many efforts have been devoted to the construction and structural optimization of well-ordered organic-inorganic nanolayers from monofunctional organosilane surfactants [1-3]. The organization process of such building blocks has been extensively investigated and is known to be governed mainly by the hydrophobic effect arising from a competition of attractive and repulsive interactions between inorganic polar heads, organic nonpolar tails, solvent and water molecules [4, 5]. Such interactions guide the nonpolar chains to aggregate and polar heads to maximize their exposure to the surrounding aqueous medium thus forming structures such as bilayers [6], micelles [7], or vesicles [8]. Finally, van der Waals forces appear between alkyl chains whereas hydrogen bonds and then stronger covalent bonds are formed between inorganic heads thus conferring thermal and mechanical stability to films [9, 10]. This study aims to investigate the effect on nanolayer structures of a second polar group located at the chain termination of alkylsilane building blocks. As intermolecular interactions which direct the assembly process are strongly dependent on the chemical composition of precursors, it is expected that the presence of a second polar endgroup will significantly affect these weak interactions thus leading to an alternative structure of nanolayers. Monofunctional hexadecyltrimethoxysilane (HDTMS) and bifunctional 11bromoundecyltrimethoxysilane (BUDTMS) were used independently as building blocks to produce organicinorganic nanolayers. Structures of these solid thin films were then sequentially characterized and compared after solution assembly and deposition on silicon substrates.