Patterns of particles generated by surface charges

Feb 04, 2014 by Florian Aigner
Ordered, crystal-like structures

Tuning the material structure at the nanoscale level can be really hard to achieve – but what if we had small particles, which assemble all by themselves, creating the required structure? At the Vienna University of Technology (TU Wien), the phenomenon of self-assembly is being investigated by studying inhomogeneously charged particles. Depending on different parameters, they can form gel-like or crystal-like structures. This kind of self-assembly holds great promise for nanotechnology.

Micro Particles with Specially Structured Surfaces

Emanuela Bianchi is a scientist in Prof. Gerhard Kahls research group at the Institute for Theoretical Physics of the Vienna University of Technology. In her computer simulations, she reproduces the bahavior of which are no bigger than a few micrometers – comparable to viruses or small bacteria. She is especially interested in nanoparticles with a complicated surface, consisting of different kinds of patches distinguished by different physical properties.

Recent work (funded via an Elise Richter Fellowhip by the FWF) has focused on particles with inhomogeneously charged surface regions: The majority of the particle carries negative electric charge, but the polar regions on the top and at the bottom of the particle are positively charged. "Due to the fact that like charges repel while opposite charges attract each other," says Emanuela Bianchi, "our particles tend to align in such a way that the pole of one particle points towards the equator of the other." But when many of these particles interact, things get more complicated.

Computer simulations have now been able to show how these particles behave when they are trapped between two planes so that they have to align in quasi two dimensional structures. The results showed that there are different possible configurations: Sometimes the particles are tightly packed in a simple hexagonal structure, which is well known from crystals. Sometimes, less ordered gel-like structures emerge, with interconnected rings of five or six particles.

Disordered gel-like structures - with interconnected rings

"With our model, we can find out which parameters determine the emerging ," says Emanuela Bianchi. The size of the positively charged polar patches plays an especially important role. Spheres on which the border between negative and positive charge is at 45 degrees latitude create much more ordered structures than particles on which this border is closer at the pole, at 60 degrees. The result can also be influenced by tuning the electrical charge of the floor plate on which the particles rest – a parameter which is very easy to control in an experiment. Such a parameter controls the size of the aggregates and can even be responsible for a complete suppression of the particle aggregation.

Materials with Taylor Made Properties

Understanding the of microparticles opens the door to designing particles which automatically form taylor-made structures. Depending on the microscopic alignment of the particles, they create surface types with different densities and different responses to external stimuli (e.g. elcetromagnetic fields). This means that self-assembled structures could for instance be used to create filters with tunable porosity. "Especially for biomedical applications, this could have many possible applications," says Emanuela Bianchi.

Explore further: Chemically driven micro- and nanomotors

More information: "Self-Assembly of Heterogeneously Charged Particles under Confinement." Emanuela Bianchi, Christos N. Likos, and Gerhard Kahl. ACS Nano 2013 7 (5), 4657-4667. DOI: 10.1021/nn401487m

add to favorites email to friend print save as pdf

Related Stories

Creating nanostructures from the bottom up

Apr 24, 2012

Microscopic particles are being coaxed by Duke University engineers to assemble themselves into larger crystalline structures by the use of varying concentrations of microscopic particles and magnetic fields.

Spheres can form squares

May 24, 2013

Everybody who has tried to stack oranges in a box knows that a regular packing of spheres in a flat layer naturally leads to a hexagonal pattern, where each sphere is surrounded by six neighbours in a honeycomb-like ...

Flowing structures in soft crystals

Aug 08, 2011

What is common to blood, ink and gruel? They are all liquids in which tiny particles are suspended – so called “colloids”. In some of these liquids, the particles form groups (clusters), which ...

Recommended for you

Chemically driven micro- and nanomotors

Dec 17, 2014

At least since the movie "The Fantastic Voyage" in 1966, in which a submarine is shrunk down and injected into the blood stream of a human, people have been toying with the idea of sending tiny "micromachines" ...

Pyramid nanoscale antennas beam light up and down

Dec 17, 2014

Researchers from FOM Institute AMOLF and Philips Research have designed and fabricated a new type of nanoscale antenna. The new antennas look like pyramids, rather than the more commonly used straight pillars. ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.