The surfactant-mediated shape evolution of titanium dioxide anatase nanocrystals in nonaqueous media was studied. The shape evolves from bullet and diamond structures to rods and branched rods. The modulation of surface energies of the different crystallographic faces through the use of a surface selective surfactant is the key parameter for the shape control.

The surface of a fused silica and oxidized silicon wafer (SiO2/Si(100)) was treated with (4-aminophenyl)trimethoxysilane (1), (3-aminopropyl)triethoxysilane (2), (3-aminopropyl)diethoxymethylsilane (3), and (3-aminopropyl)ethoxydimethylsilane (4) in solution. The thickness of thus formed aminosilane layers was determined with ellipsometry. In most cases silane coupling agents produce monolayers of 6−10 Å thickness, but reagent 2 gives multilayers with variable thickness (6−100 Å) depending upon the dipping time. The aminosilane layers were allowed to react with 4-nitrobenzaldehyde, and formation of the corresponding imines was confirmed by UV−vis spectroscopy. Relative surface density of the amines was calculated from the observed absorbance. In aqueous medium the imines were easily hydrolyzed to regenerate the amine group. The process, the formation, and the subsequent hydrolysis of the imines, can be repeated several times without any noticeable degradation of the absorption characteristics. The ellipsometric data and the measured absorbance show that 3 gives the most uniform molecular layer with the highest surface density of the amine functionality. Meanwhile, 2 provides multilayers lacking uniformity, and the other reagents produce uniform thin layers but with lower surface density of the amine.

Novel polymeric nanoparticles were prepared through the chain collapse of linear polymers driven by noncovalent cross-linking of dendritic self-complementary hydrogen-bonding units (SHB). Random copolymers containing SHB units, poly[(methyl methacrylate)-r-2-((3,5-bis(4-carbamoyl-3-(trifluoromethyl)phenoxy)benzyloxy)carbonylamino)ethyl methacrylate] (A1, A2), were synthesized with various incorporation ratios by reversible addition-fragmentation chain transfer (RAFT) polymerization. Dramatically different behavior was observed depending on the level of incorporation of the supramolecular units. At high loadings of A2 (6% SHB incorporation), intramolecular chain collapse is favored, resulting in the formation of well-defined polymer nanoparticles, which were characterized by scanning force microscopy (SFM), dynamic light scattering (DLS), and viscosity studies. In contrast, analysis of copolymer A1 (1% SHB incorporation) revealed that chain collapse occurred primarily through intermolecular interactions leading to large aggregates.

Evolution of supramolecular chirality from self-assembly of achiral compounds and control over its handedness is closely related to the evolution of life and development of supramolecular materials with desired handedness. Here we report a system where the entire process of induction, control and locking of supramolecular chirality can be manipulated by light. Combination of triphenylamine and diacetylene moieties in the molecular structure allows photoinduced self-assembly of the molecule into helical aggregates in a chlorinated solvent by visible light and covalent fixation of the aggregate via photopolymerization by ultraviolet light, respectively. By using visible circularly polarized light, the supramolecular chirality of the resulting aggregates is selectively and reversibly controlled by its rotational direction, and the desired supramolecular chirality can be arrested by irradiation with ultraviolet circularly polarized light. This methodology opens a route to ward the formation of supramolecular chiral conducting nanostructures from the self-assembly of achiral molecules.

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New soluble polyimides with improved adhesion to copper were synthesized from 6,4‘-diamino-2-phenylbenzimidazole (BIA) and 2,2‘-bis(trifluoromethyl)-4,4‘-diaminobiphenyl (TFDB) with 3,3‘,4,4‘-benzophenone tetracarboxylic dianhydride (BTDA) via one-pot synthetic method using N-methylpyrrolidone (NMP) as a solvent. Precipitation or gelation did not occur during imidization, and the synthesized polyimides having inherent viscosity values of 0.86−1.74 dL/g were dissolved well in polar aprotic solvents and phenolic solvents. Flexible and fingernail-creasable films were formed on casting. T g values of the polyimides were in the range of 320−351 °C and 5% weight loss in nitrogen occurred above 540 °C in all cases. The polyimides containing an equimolar amount of BIA and TFDB showed good adhesion to copper without any adhesion promoters. Water absorption and dielectric constant of the polyimides were in the ranges of 0.57−1.18% and 2.74−2.94, respectively. The polyimides containing a higher content of benzimidazole rings exhibited higher adhesion to copper.

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