Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Silicone liquid crystal stiffens with repeated compression

30.04.2013
Rice University researchers say discovery may point toward self-healing materials
Squeeze a piece of silicone and it quickly returns to its original shape, as squishy as ever. But scientists at Rice University have discovered that the liquid crystal phase of silicone becomes 90 percent stiffer when silicone is gently and repeatedly compressed. Their research could lead to new strategies for self-healing materials or biocompatible materials that mimic human tissues.

A paper on the research appeared this month in Nature’s online journal Nature Communications.

Silicone in its liquid crystal phase is somewhere between a solid and liquid state, which makes it very handy for many things. So Rice polymer scientist Rafael Verduzco was intrigued to see a material he thought he knew well perform in a way he didn’t expect. “I was really surprised to find out, when my student did these measurements, that it became stiffer,” he said. “In fact, I didn’t believe him at first.”

The researchers had intended to quantify results seen a few years ago by former Rice graduate student Brent Carey, who subjected a nanotube-infused polymer to a process called repetitive dynamic compression. An astounding 3.5 million compressions (five per second) over a week toughened the material, just like muscles after a workout, by 12 percent.
What Verduzco and lead author/Rice graduate student Aditya Agrawal came across was a material that shows an even stronger effect. They had originally planned to study liquid crystal silicone/nanotube composites similar to what Carey tested, but decided to look at liquid crystal silicones without the nanotubes first. “It’s always better to start simple,” Verduzco said.

Silicones are made of long, flexible chains that are entangled and knotted together like a bowl of spaghetti. In conventional silicones the chains are randomly oriented, but the group studied a special type of silicone known as a liquid crystal elastomer. In these materials, the chains organize themselves into rod-shaped coils. When the material was compressed statically, like squeezing a piece of Jell-O or stretching a rubber band, it snapped right back into its original shape. The entanglements and knots between chains prevent it from changing shape. But when dynamically compressed for 16 hours, the silicone held its new shape for weeks and, surprisingly, was much stiffer than the original material.

“The molecules in a liquid crystal elastomer are like rods that want to point in a particular direction,” Verduzco said. “In the starting sample, the rods are randomly oriented, but when the material is deformed, they rotate and eventually end up pointing in the same direction. This is what gives rise to the stiffening. It’s surprising that by a relatively gentle but repetitive compression, you can work out all the entanglements and knots to end up with a sample where all the polymer rods are aligned.”

Before testing, the researchers chemically attached liquid crystal molecules – similar to those used in LCD displays — to the silicones. While they couldn’t see the rods, X-ray diffraction images showed that the side groups – and thus the rods – had aligned under compression. “They’re always coupled. If the side group orients in one direction, the polymer chain wants to follow it. Or vice versa,” Verduzco said.

The X-rays also showed that samples heated to 70 degrees Celsius slipped out of the liquid crystal phase and did not stiffen, Verduzco said. The stiffening effect is reversible, he said, as heating and cooling a stiffened sample will allow it to relax back into its original state within hours.

Verduzco plans to compress silicones in another phase, called smectic, in which the polymer rods align in layers. “People have been wanting to use these in displays, but they’re very hard to align. A repetitive compression may be a simple way to get around this challenge,” he said.

Since silicones are biocompatible, they can also be used for tissue engineering. Soft tissues in the body like cartilage need to maintain strength under repeated compression and deformation, and liquid crystal elastomers exhibit similar durability, he said.

The paper’s co-authors include Carey, a Rice alumnus and now a scientist at Owens Corning; graduate student Alin Chipara; Yousif Shamoo, a professor of biochemistry and cell biology; Pulickel Ajayan, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of mechanical engineering and materials science, chemistry and chemical and biomolecular engineering; and Walter Chapman, the William W. Akers Professor of Chemical and Biomolecular Engineering, all of Rice; and Prabir Patra, an assistant professor of mechanical engineering at the University of Bridgeport with a research appointment at Rice. Verduzco is an assistant professor of chemical and biomolecular engineering.

The research was supported by an IBB Hamill Innovations Grant, the Robert A. Welch Foundation, the National Science Foundation and the National Institutes of Health, through the National Institute of Allergy and Infectious Diseases.

Read the abstract at http://www.nature.com/ncomms/journal/v4/n4/full/ncomms2772.html.

Follow Rice News and Media Relations via Twitter @RiceUNews.

Related Materials:
Verduzco Laboratory: http://verduzcolab.blogs.rice.edu

Mike Williams | EurekAlert!
Further information:
http://www.rice.edu

More articles from Materials Sciences:

nachricht An innovative high-performance material: biofibers made from green lacewing silk
20.01.2017 | Fraunhofer-Institut für Angewandte Polymerforschung IAP

nachricht Treated carbon pulls radioactive elements from water
20.01.2017 | Rice University

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Helmholtz International Fellow Award for Sarah Amalia Teichmann

20.01.2017 | Awards Funding

An innovative high-performance material: biofibers made from green lacewing silk

20.01.2017 | Materials Sciences

Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery

20.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>