MIT - Page 6

Researchers from MIT have fabricated a functional dialysis membrane from a sheet of graphene. The team’s membrane is able to filter out nanometer-sized molecules from aqueous solutions up to 10 times faster than state-of-the-art membranes, with the graphene itself being up to 100 times faster. The graphene membrane is also very thin; It's less than 1 nanometer thick, while the thinnest existing membranes are about 20 nanometers thick.

Dialysis can be generally described as the process by which molecules filter out of one solution by diffusing through a membrane, into a more dilute solution. The most recognizable form is hemodialysis, which removes waste from blood, but scientists also use dialysis for many other applications, like purifying drugs, removing residue from chemical solutions, and more, typically by allowing the materials to pass through a porous membrane.

MIT researchers have found that a flake of graphene, when brought in close proximity with two superconducting materials, can "borrow" some of those materials' superconducting qualities. When graphene is sandwiched between superconductors, its electronic state changes dramatically, even at its center.

The researchers showed that graphene's electrons, formerly behaving as individual particles, instead pair up in "Andreev states"—a fundamental electronic configuration that allows a conventional, non-superconducting material to carry a "supercurrent," an electric current that flows without dissipating energy.

Researchers at MIT have developed a technique that uses graphene as a kind of copy machine, to transfer intricate crystalline patterns from an underlying semiconductor wafer to a top layer of identical material.

As a great deal of money is spent in the semiconductor industry on wafers that serve as the substrates for microelectronics components, which can be turned into transistors, light-emitting diodes etc., this method may help reduce the cost of wafer technology and enable devices made from more exotic, higher-performing semiconductor materials than conventional silicon.

Scientists at MIT, along with researchers from IBM, the University of California at Los Angeles, and Kyungpook National University in South Korea, have found a way to produce graphene with fewer wrinkles, and to iron out the wrinkles that do appear. The team reports that the techniques successfully produce wafer-scale, "single-domain" graphene - single layers of graphene that are uniform in both atomic arrangement and electronic performance.

After fabricating and then flattening out the graphene, the researchers tested its electrical conductivity. They found each wafer exhibited uniform performance, meaning that electrons flowed freely across each wafer, at similar speeds, even across previously wrinkled regions.

Researchers at MIT and National Chiao Tung University have designed a graphene oxide-based system that could make it possible to capture and analyze individual cells from a small sample of blood, potentially leading to very low-cost diagnostic systems that could be used almost anywhere.

The new system, based on specially treated sheets of graphene oxide. The team explains that the key to the new process is heating the graphene oxide at relatively mild temperatures. This low-temperature annealing makes it possible to bond particular compounds to the material's surface. These compounds in turn select and bond with specific molecules of interest, including DNA and proteins, or even whole cells. Once captured, those molecules or cells can then be subjected to a variety of tests.

Researchers at MIT have designed a strong and lightweight material, by compressing and fusing flakes of graphene. The new material, a sponge-like configuration with a density of just 5%, can have a strength 10 times that of steel. This work could pose an interesting way of transforming graphene into useful 3D objects and items.

The team developed the product by using a combination of both heat and pressure, compressing and fusing the flakes of graphene together. This process produced a strong, stable structure whose form resembles that of some corals and microscopic creatures called diatoms. These shapes, which have an enormous surface area in proportion to their volume, proved to be remarkably strong.

Graphene has exciting potential for use in various implants and other medical applications, but since graphene is stiff and biological tissues are soft, there is a concern among scientists that a graphene implant could suddenly heat up and "fry" the surrounding cells when any power is applied to make it function. Researchers from MIT and Tsinghua University in China have simulated the way in which electrical power produces heat between a simple cell membrane and a single layer of graphene, to find if it is possible to prevent the heat buildup.

The team found that this is possible by using a very thin, in-between layer of water. By controlling the thickness of this in-between water layer, the collaborative team could carefully manipulate the quantity of heat transferred between biological tissue and graphene. They also fixed the critical power required to apply to the graphene layer, without causing the cell membrane to burn.

Researchers at MIT have found a way to make composite materials using large area graphene films, in which large numbers of layers are stacked in an orderly manner, without having to stack each layer individually. This could enable creating composite materials containing hundreds of layers and open the door to various possibilities for designing new, easy-to-manufacture composites for optical devices, electronic systems, and more.

A major obstacle in creating graphene-based composites has been that graphene sheets and particles have a strong tendency to adhere together, so just stirring them into a batch of liquid resin before it sets is inefficient. The new technique could go a long way in solving this - while the process is more complex than it sounds, at the heart of it is a technique similar to that used to make puff pastry common in many desserts. A layer of material — dough, or graphene, in this case — is spread out flat. Then, the material is doubled over on itself, pounded or rolled out, and then doubled over again, and again, and again. With each fold, the number of layers doubles, thus producing an exponential increase in the layering. Just 20 simple folds would produce more than a million perfectly aligned layers.

Researchers at the Massachusetts Institute of Technology have discovered that graphene sheets could be used to make chips up to a million times faster. The researchers found that slowing the speed of light to the extent that it moves slower than flowing electrons can create an "optical boom", the optical equivalent of a sonic boom.

The researchers managed the complicated task of slowing the speed of light by using the honeycomb shape of carbon to slow photons to several hundredths of their normal speed in a free space. Meanwhile, the characteristics of graphene speed up electrons to a million meters a second, or around 1/300 of the speed of light in a vacuum. The optical boom is caused when the electrons passing though the graphene reach the speed of light, effectively breaking its barrier in the carbon honeycomb and causing a shockwave of light.

Researchers at MIT and Harvard University fabricated nanoscrolls made from graphene oxide flakes for water purification applications, at a much lower cost than that of graphene membranes. The team was able to control the dimensions of each nanoscroll, using both low- and high-frequency ultrasonic techniques.

The researchers say that these nanoscrolls could also be used as ultralight chemical sensors, drug delivery vehicles, and hydrogen storage platforms, in addition to water filters. Also, the ability to tune the dimensions of these architectures may open a window to industry, in combination with the more affordable production costs.