Solid and liquid at the same time

January 17, 2018, Vienna University of Technology
Particles forming regular layers. Credit: TU Wien

Microscopically small particles can spontaneously self-assemble into complex layered structures with remarkable properties, according to calculations performed at the TU Wien.

There are many ways to create new, innovative materials. One of the most interesting is a process whereby self-assemble to form complex structures. This process, referred to as "self-organisation," opens up some remarkable opportunities as has now been demonstrated by computer simulations performed at TU Wien. Simple macromolecules are able to form layered systems that can be simultaneously solid and liquid within a wide temperature range.

Repulsive and attractive charges

"The basic concept is one that is exploited widely in nature," explains Professor Gerhard Kahl of the Institute of Theoretical Physics at TU Wien. "Viruses and bacteria often exhibit surface charges. This means that they either attract or repel one another, depending on the type of charge they are carrying. As a result, selective bonding can occur between these entities, allowing them to assemble themselves into interesting, functional structures."

A similar process is also possible with man-made particles – for example, small (colloidal) spheres to which a positive electrical charge is applied at two opposite surface regions. If the ambient conditions are appropriate, such particles can self-assemble to form a two-dimensional layer. The particles then become tightly packed, forming a hexagonal pattern, with the charged surface regions of the particles aligned so that they form strong attractive bonds. This bonding pattern makes the layer extremely stable.

The system is reminiscent of warm chocolate wafers—with solid and liquid layers. Credit: TU Wien

As Emanuela Bianchi and Silvano Ferrari from Gerhard Kahl's working group have demonstrated, this allows an interesting phenomenon to occur, namely that several such layers can then join together simultaneously. Additional particles can can then occupy positions between the layers, establishing strong bonds between these . These bonding particles fix the layers in place, meaning that they can no longer shift relative to one another; thus a stable, multi-layered is formed completely autonomously through self-organisation of random particles that happen to be passing by.

Both solid and liquid: the mini chocolate wafer

The special characteristics of these structures become apparent when the temperature is raised: "The bonds within the individual layers are much stronger than the bonds between the layers," explains Gerhard Kahl. "If the temperature is increased, it is the weaker bonds between the layers that break first; the particles can then move freely as a liquid whilst the layers themselves remain stable." This effect is similar to a chocolate wafer in the summer heat, with liquid chocolate sandwiched between solid, stable wafer layers. "This is a remarkable phenomenon. We are dealing with a unique material that consists of only one type of particles, yet can form a structure that comprises both solid and liquid layers at the same time."

This scenario can be observed over a wide temperature range; it is only when the temperature is so high that even the stable bonds within the individual layers are broken that the structure falls apart and melts completely. Until then, the system demonstrates an exceptional ability to self-heal: even when damaged, it is soon repaired automatically by randomly passing particles.

Experiments have already started to test the potential uses of these new ideas. There are many possible uses for structures of this kind. "Such structures would allow us to precisely control the transportation of via suble changes in ," says Gerhard Kahl. This could be used in medicine, for example, in order to transport medication to exactly the appropriate place in the body.

Explore further: Artificial 2-D crystals modified at the touch of a button

More information: Silvano Ferrari et al. Spontaneous assembly of a hybrid crystal-liquid phase in inverse patchy colloid systems, Nanoscale (2016). DOI: 10.1039/C6NR07987C

Related Stories

Artificial 2-D crystals modified at the touch of a button

September 30, 2016

Charged particles can form via self-organization processes an unexpectedly large range of crystal structures entirely by themselves. A research team with participants from TU Wien has demonstrated how easily the formation ...

Patterns of particles generated by surface charges

February 4, 2014

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 ...

Ice skating on water, even when it is really cold

November 27, 2017

The outermost layer of ice behaves like liquid water, even at a temperature of –30°C. Physicists at AMOLF have irrefutably demonstrated this using a modern surface-sensitive measuring technique. At lower temperatures, ...

New technique produces tunable, nanoporous materials

October 27, 2017

A collaborative group of researchers including Petr Kral, professor of chemistry at the University of Illinois at Chicago, describe a new technique for creating novel nanoporous materials with unique properties that can be ...

Nano world: Where towers construct themselves

June 2, 2014

Imagine a tower builds itself into the desired structure only by choosing the appropriate bricks. Absurd – and however, in the nano world this is reality: There an unordered crowd of components can initiate the formation ...

Flowing structures in soft crystals

August 8, 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 form regular ...

Recommended for you

Observing cellular activity, one molecule at a time

May 21, 2018

Proteins and molecules assemble and disassemble naturally as part of many essential biological processes. It is very difficult to observe these mechanisms, which are often complex and take place at the nanometer scale, far ...

A soft solution to the hard problem of energy storage

May 18, 2018

It's great in the lab, but will it actually work? That's the million-dollar question perpetually leveled at engineering researchers. For a family of layered nanomaterials, developed and studied at Drexel University—and ...

New blood test rapidly detects signs of pancreatic cancer

May 17, 2018

Pancreatic cancer is expected to become the second deadliest cancer in the United States by 2030. It is tough to cure because it is usually not discovered until it has reached an advanced stage. But a new diagnostic test ...

0 comments

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.