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

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Writing and deleting magnets with lasers

Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...

Im Focus: Gamma-ray flashes from plasma filaments

Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.

The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...

Im Focus: Basel researchers succeed in cultivating cartilage from stem cells

Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.

Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...

Im Focus: Like a wedge in a hinge

Researchers lay groundwork to tailor drugs for new targets in cancer therapy

In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...

Im Focus: The Future of Ultrafast Solid-State Physics

In an article that appears in the journal “Review of Modern Physics”, researchers at the Laboratory for Attosecond Physics (LAP) assess the current state of the field of ultrafast physics and consider its implications for future technologies.

Physicists can now control light in both time and space with hitherto unimagined precision. This is particularly true for the ability to generate ultrashort...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

IWOLIA: A conference bringing together German Industrie 4.0 and French Industrie du Futur

09.04.2018 | Event News

 
Latest News

Diamond-like carbon is formed differently to what was believed -- machine learning enables development of new model

19.04.2018 | Materials Sciences

Electromagnetic wizardry: Wireless power transfer enhanced by backward signal

19.04.2018 | Physics and Astronomy

Ultrafast electron oscillation and dephasing monitored by attosecond light source

19.04.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>