Manufacturing Bits: Oct. 15

Better Beer
Rice University has devised a polymer material that could boost the properties of natural gas, beer and soda.

By adding modified, single-atom-thick graphene nanoribbons (GNRs) to thermoplastic polyurethane (TPU), Rice’s polymer material could make it more practical for vehicles to run on compressed natural gas. The material is far more impermeable to pressurized gas and lighter than today’s metal gas tanks.

The polymer material makes it 1,000 times harder for gas molecules to escape due to the even dispersion of GNRs, according to researchers. A TPU composite film containing hexadecyl-functionalized low-defect graphene nanoribbons (HD-GNRs) was produced by using a solution casting methodology, according to researchers.

An electron microscope image shows graphene nanoribbons embedded in a block copolymer. The composite material created at Rice University shows promise for containing compressed natural gas and for food packaging. (Credit: Tour Group/Rice University)

The HD-GNRs were distributed in the mix, which, in turn, led to a phase separation of the TPU. The GNRs were 200- to 300nm in width. The incorporation of HD-GNRs improved the mechanical properties of the composite films.

Typically, graphene, namely the GNRs, are difficult to produce in bulk quantities. But recently, researchers from Rice devised a breakthrough “unzipping” technique for turning multiwalled carbon nanotubes into GNRs. “These are being produced in bulk, which should also make containers cheaper,” said Rice chemist James Tour, on the university’s Web site.

“The idea is to increase the toughness of the tank and make it impermeable to gas,” Tour said. “This becomes increasingly important as automakers think about powering cars with natural gas. Metal tanks that can handle natural gas under pressure are often much heavier than the automakers would like.”

The improved properties could also lead to applications in food packaging. Over time, gas molecules can move through rubber or plastic. “It took years for scientists to figure out how to make a plastic bottle for soda. And even now, bottled soda goes flat after a period of months,” he said.

Bottles that are impermeable could lead to beer with a longer shelf life. “Beer has a bigger problem and, in some ways, it’s the reverse problem,” he said. “Oxygen molecules get in through plastic and make the beer go bad.”

Printing Invisible Materials
Metamaterials are artificial materials containing arrays of metal nanostructures. Some metamaterials are able to bend light around objects, rendering them invisible. But they only interact with light over a very narrow range of wavelengths, according to researchers.

Researchers from Riken have developed a nanoimprint technology that could fabricate visible-light-bending metamaterials. The metamaterials can interact with light at visible wavelengths.

Riken created a silica-based metamaterial containing an array of split-ring resonators. This includes thin gold rings with two small breaks at the top and bottom.

Metamaterials are fabricated by e-beam lithography, which is a slow process. E-beam lithography is also limited to producing arrays of several hundred square micrometers in area.

Riken, however, made its structures using nanoimprint lithography. In this process, a master mold is created. Then, the pattern is transferred to a thin polymer film. With this approach, researchers have created split rings, which were approximately 212nm across and 54nm high.

In addition, they devised an array of 360 million split-ring resonators across a 5mm square area using nanoimprint. “This is, to the best of our knowledge, the world’s largest two-dimensional split-ring resonator array metamaterial for visible light,” said Takuo Tanaka from Riken, on the entity’s Web site. “Our next step will be to create much larger metamaterials, to make them three dimensional, and to reduce the operation wavelength.”

Enabling DSA
The University of Illinois has developed a new microfluidic technology that could help drive directed self-assembly (DSA) from the lab to the fab.

The big challenge with DSA is to direct and control the materials for the desired functionality. To solve the problem, researchers devised a specialized microfluidic platform. A microfluidic-based technology is employed to form aligned molecular structures

According to researchers, peptide precursor materials can be aligned and oriented during their assembly into polypeptides. This, in turn, is accomplished using tailored flows in microfluidic devices.

The formation of aligned synthetic oligopeptide nanostructures is accomplished using planar extensional flows, according to researchers. Fluidic-directed assembly of the structures allows for manipulation at the nanoscales.

Reversible assembly and disassembly of synthetic oligopeptide nanostructures. Source: University of illinois.

“Our approach has the potential to enable reproducible and reliable fabrication of advanced materials,” said Amanda Marciel, a graduate student at University of Illinois, on the entity’s Web site. “Achieving nanoscale ordering in assembled materials has become the primary focus of recent efforts in the field. These approaches will ultimately lead to desired morphology in functional materials, which will enhance their ability to capture and store energy.”

The technology could be used for the development of photovoltaic devices, solid-state lighting, energy harvesting, and catalytic processes. Another application is to assemble the organic equivalent of typical semiconducting materials.