Complex structures, such as living organisms or highly structured materials, have in common the fact that their inherent complexity may be accounted for by the tangled organization of a vast number of simple units. The complex behavior arises not necessarily from the atomic structure of the system, but from the orderly assembly of all, or part, of its constituents.[1,2] Self-assembly of synthetic soft-matter componentssuch as polymers, liquid crystals, surfactants, colloids, and organic/inorganic hybrids-results in regular hierarchically organized structures. [3][4][5] The importance of combining sol-gel methods and self-assembly routes to synthesize hierarchically structured organic/inorganic materials, with potential applications in the design of ion-transport microdevices, has been highlighted recently.[5]Silsesquioxanes ((RO) 3 -Si-R′-Si-(OR) 3 , where R and R′ are organic groups) and organosilanes (R′-Si-X 3 , where X = OR or Cl) are examples in which hierarchically ordered self-assembled architectures with well-defined morphologies at the macroscopic scale-such as ribbons stacked into lamellae, [6][7][8][9] 2D hexagonal structures, [9] twisted helical fibers with controlled handedness, [10] hollow tubes and spheres, [11] ladderlike superstructures, [12] and bilayered lamellar packing [13][14][15] are induced by weak interactions between the R′ organic spacers (hydrogen bonding, hydrophobic interactions, and p-p interactions).Despite the fact that work on silsesquioxanes has produced hierarchically ordered architectures, [6][7][8][9][10][11][12] so far the self-assembly of the simpler trifunctional alkylsilanes has been reported only sporadically. [13][14][15] In these examples, the design strategy relies on the self-organization of organophilic precursor molecules that become amphiphilic as hydrolysis proceeds to form hydrophilic silanol groups. As the hydrophilic parts (head groups) of alkylsilanetriols occupy less space than the hydrophobic ones, lamellar packing is favored. This anisotropic aggregation mechanism of alkyltrihydroxysilane species resembles that of amphiphilic surfactants and phospholipid molecules. Like the L-phase (lamellar phase) of phospholipids, alkylsilanes are characterized by a bimolecular layered pattern of stacks of alkyl chains perpendicular to the layers. The only known examples of bilayered lamellar packing in alkylsilanes are the microcrystalline poly(octadecylsiloxane)s prepared from n-alkyltrichlorosilanes, [13] and the hybrids synthesized from triethoxy- [14] and trimethoxy-based [15] alkylsilanes. Hydrophobic interactions between the organic chains are the main force driving the formation of these highly ordered packing structures. Although the relationship between structural complexity and self-assembly mechanisms has been given much consideration, the essential role played by higher organizing principles in determining emergent physical phenomena in soft-matter complex structures, although recognized (e.g., for the unpredictable electronic features of cholesterol-stilben...

The chemical and structural nature of powders prepared from the zinc acetate-derived precursor using the sol−gel route is discussed. The influence of the synthesis temperature and of the hydrolytic catalyst on the structural features of the powder is focused on the basis of X-ray powder diffraction (XRPD) and extended X-ray absorption fine structure (EXAFS) measurements and complemented with density and thermoanalysis (TG-DTA) results. EXAFS and XRPD results show that no-washed nanoparticulate powders are composed of a mixture of ZnO (wurtzite), zinc acetate, and zinc hydroxyacetate. The latter has a layered structure typical of hydroxy double salts (HDS). The main component of no-washed powders is always unreacted zinc acetate solid but the relative amount of the zinc-based compounds depends on the nature of the hydrolytic catalyst, hydrolysis ratio, and of synthesis temperature. According to the proportion of the three zinc-based compounds, three families of powders could be distinguished. The amount of ZnO nanoparticles (1.6 ± 0.6 nm) decreases as the synthesis temperature increases, as the hydrolysis ratio decreases, or by changing from basic to acid catalysis. This finding suggests that the formation of zinc compounds is controlled by the equilibrium between hydrolysis−condensation and complexation−reprecipitation reactions.

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