Faysal Ilhan

Self-assembly of nanoparticles into structured spherical and networkaggregates

Multi-scale ordering of materials is central for the application of molecular systems in macroscopic devices. Self-assembly based on selective control of non-covalent interactions provides a powerful tool for the creation of structured systems at a molecular level, and application of this methodology to macromolecular systems provides a means for extending such structures to macroscopic length scale. Monolayer-functionalized nanoparticles can be made with a wide variety of metallic and non-metallic cores, providing a versatile building block for such approaches. Here we present a polymer-mediated ‘bricks and mortar’ strategy for the ordering of nanoparticles into structured assemblies. This methodology allows monolayer-protected gold particles to self-assemble into structured aggregates while thermally controlling their size and morphology. Using 2-nm gold particles as building blocks, we show that spherical aggregates of size 97 ± 17 nm can be produced at 23 °C, and that 0.5–1 µm spherical assemblies with (5–40) × 105 individual subunits form at -20 °C. Intriguingly, extended networks of ∼50-nm subunits are formed at 10 °C, illustrating the potential of our approach for the formation of diverse structural motifs such as wires and rods. These findings demonstrate that the assembly process provides control over the resulting aggregates, while the modularity of the ‘bricks and mortar’ approach allows combinatorial control over the constituents, providing a versatile route to new materials systems.

Hydrophobic monolithic aerogels by nanocasting polystyrene on amine-modified silica

We describe a three-dimensional core–shell structure where the core is the assembly of nanoparticles that comprises the skeletal framework of a typical silica aerogel, and the shell is polystyrene. Specifically, the mesoporous surfaces of silica were first modified with amines by co-gelation of tetramethylorthosilicate (TMOS) and 3-aminopropyltriethoxysilane (APTES). Next, styrene moieties were attached to the amines by reaction with p-chloromethylstyrene. Finally, dangling styrene moieties were crosslinked by a free-radical polymerization process initiated by AIBN and styrene, p-chloromethylstyrene or 2,3,4,5-pentafluorostyerene introduced in the mesopores. Polystyrene crosslinked aerogels are mechanically strong, lightweight (0.41–0.77 g cm−3), highly porous materials (they consist of ca. 63% empty space, with a BET surface areas in the range of 213–393 m2 g−1). Their thermal conductivity (0.041 W m−1 K−1) is comparable to that of glass wool. Hydrophobicity, however, is the property that sets the new material apart from analogous polyurea and epoxy crosslinked aerogels. The contact angles of water droplets on disks cut from larger monoliths are >120°. (By comparison, the contact angle with polyurea crosslinked aerogels is only ca. 60°.) Polystyrene crosslinked aerogel monoliths float on water indefinitely, while their polyurea counterparts absorb water and sink within minutes.

Binary and Ternary Polymer‐Mediated “Bricks and Mortar” Self‐Assembly of Gold and Silica Nanoparticles

An amine-functionalized polymer has been used to simultaneously assemble carboxylic acid functionalized gold and silica nanoparticles into extended aggregates. This three component assembly process is highly versatile, with aggregate morphology controlled through stoichiometry, and nanoparticle segregation within the aggregate regulated through order of component addition.

Bricks and mortar self-assembly of nanoparticles

Abstract The use of nanoparticles and polymers bearing complementary recognition elements provides a versatile method for the formation of nanoparticle aggregates. This assembly process is highly dependent upon the primary and secondary recognition elements attached to the polymer and nanoparticle; we have observed variations in aggregate morphology that are directly correlated to supramolecular events at the colloid–polymer interface.

Tuneable electrochemical interactions between polystyrenes with anthracenyl and tetrathiafulvalenyl sidechains

Polymer 4 and its monomeric counterpart 3 exhibit electrochemically tuneable interactions with anthracene polymer 2 and a structurally similar monomer 1 and seen by the variation of the oxidation waves of TTF groups and the fluorescence of the anthracene.

Use of Diels-Alder Cyclopolymerizations in the Photocuring of Polymers

Radiation curable polymers are needed for use in space rigidizable inflatable structures (antenna supports, habitats, rovers) for future NASA missions. One approach developed at NASA Glenn utilizes the Diels-Alder trapping of bisdienes (o-xylylenols) generated by the photolysis of o-methylphenyl ketones with bisdienophiles (bismaleimides and bisacrylates). A variety of polyimides and polyesters have been prepared with this chemistry and their properties evaluated. The glass transition temperatures of these resins varied from –27 to over 300°C depending upon monomer structures. Onsets of decomposition, measured by thermogravimetric analysis in air, were in the neighborhood of 300°C and did not vary much with monomer structure. Some monomer systems are liquids at room temperature and have the potential for use in solvent-free UV-cured coatings.

Substrate Based “Bricks-and-Mortar” Self-Assembly of Spherical Nanoparticle Aggregates

Transmission Electron Microscope (TEM) sample girds were coated with recognition element functionalized polymer 2 and exposed to solutions of a Mixed Monolayer Protected Gold Cluster (MMPC) functionalized with a complimentarily recognition element. Interactions between the polymer and MMPC bound recognition elements provide a driving force for the formation of nanoparticle aggregates. Characterization of the resulting structures by TEM revealed that anisotropic growth of structures in the sub-micrometer size regime rapidly occurred. This process was shown to be the result of the specific hydrogen-bonding interactions between the two components. Casting films of polymer 2 from solutions of decreasing concentration achieved control over the process. This lead to the increased formation of regular, circular structuresand a decrease in random nanoparticle adsorption by the film. Analysis of the size of the circular structures revealed that a maximum diameter of approximately 1150 nm was achieved after 30 minutes exposure to MMPC 1 solutions. This size was independent of the concentration of polymer 2 solutions used to cast films.

Kinetic trapping of host–guest complexes in a polymeric matrix

Diaminotriazine–flavin host–guest complexes are kinetically trapped in spin-cast polystyrene films.