Nanoscale Cubes and Spheres

Jan 03, 2007

Porous nano-objects with defined sizes and structures are particularly interesting, for example, as capsules for enzymes, a means of transport for pharmaceutical agents, or building blocks for larger nanostructures.

The production of such tiny, three-dimensional objects in a targeted and controlled manner—and as simply and efficiently as possible—remains a challenge for scientists. At the University of Minnesota, a team led by Andreas Stein has now developed an interesting new process for the production of nanoscopic cubes and spheres of silicon dioxide.

The researchers reported their trick in Angewandte Chemie. Instead of building their particles from smaller units, they used the controlled disassembly of larger, lattice-like structures.

Most conventional methods for the production of porous silicon dioxide nanoparticles suffer from the fact that the growing particles tend to aggregate (clump together), making it difficult to achieve a uniform size. The shape of the particles can hardly be influenced at all.

Stein and his team chose a backward approach, first building up a lattice structure of silicon dioxide and then disassembling it to get the shape they wanted. The “moulds” used for the lattice were tiny spheres of a plastic called polymethylmethacrylate (PMMA), which assemble themselves through “closest packing of spheres” into a colloidal crystal. Between the spheres in this structure, there are little, nearly tetrahedral and nearly octahedral spaces.

The researchers filled these cavities with a solution containing an organosilicon compound, oxalic acid, and a surfactant. This mixture hardens into a solid gel. The plastic spheres and surfactant are then burned off by heating. The surfactant leaves behind tiny pores, and the gelled organosilicon compound slowly converts to a solid silicon oxide.

What remains initially is a silicate lattice that is the negative of the packed spheres: tiny tetrahedra and octahedra attached to each other by delicate bridges. As the conversion to silicon dioxide continues, the structure shrinks until it breaks at the weakest points—the bridges. The fragments formed by this process are shaped like octahedra or smaller tetrahedra. These continue to contract until the octahedra become nearly cubic and the tetrahedra become nearly spherical, making highly uniform structures with worm-like pores.

By varying the colloidal crystals used as the mould, the size and shape of the resulting particles can be controlled. Through vapor deposition or polymer grafting, other compounds can be added to the structure. Subsequent etching away of the silicon oxide allows this new technique to be used as a starting point for nanostructures made of other materials.

Citation: Andreas Stein, et al., Shaping Mesoporous Silica Nanoparticles by Disassembly of Hierarchically Porous Structures, Angewandte Chemie International Edition, doi: 10.1002/anie.200604147

Source: Angewandte Chemie

Explore further: Tough foam from tiny sheets

add to favorites email to friend print save as pdf

Related Stories

Soaking up the sun

Jun 26, 2014

When it comes to solar power, it's a case of the more blue the better according to Victoria University of Wellington researcher Dr Jonathan Halpert.

Trapping light: A long lifetime in a very small place

Jun 16, 2014

Physicists at the University of Rochester have created a silicon nanocavity that allows light to be trapped longer than in other similarly-sized optical cavities. An innovative design approach, which mimics ...

Nano-imaging probes molecular disorder

Jun 13, 2014

Using a newly developed imaging method, LMU researchers show that thin-film organic semiconductors contain regions of structural disorder that could inhibit the transport of charge and limit the efficiency ...

Atomic force microscope systems take a tip from nanowires

May 26, 2014

(Phys.org) —In response to requests from the semiconductor industry, a team of PML researchers has demonstrated that atomic force microscope (AFM) probe tips made from its near-perfect gallium nitride nanowires ...

Recommended for you

A new way to make microstructured surfaces

51 minutes ago

A team of researchers has created a new way of manufacturing microstructured surfaces that have novel three-dimensional textures. These surfaces, made by self-assembly of carbon nanotubes, could exhibit a ...

Tough foam from tiny sheets

20 hours ago

Tough, ultralight foam of atom-thick sheets can be made to any size and shape through a chemical process invented at Rice University.

Graphene surfaces on photonic racetracks

Jul 28, 2014

In an article published in Optics Express, scientists from The University of Manchester describe how graphene can be wrapped around a silicon wire, or waveguide, and modify the transmission of light through it.

Simulating the invisible

Jul 28, 2014

Panagiotis Grammatikopoulos in the OIST Nanoparticles by Design Unit simulates the interactions of particles that are too small to see, and too complicated to visualize. In order to study the particles' behavior, he uses ...

User comments : 0