Innovative, advanced conductive polymer application development
Monday, February 01, 2016
Electrically conductive plastic got its industrial start by playing an important role in providing low-cost protection against electrostatic discharge (ESD) or electromagnetic interference (EMI) in miniaturized electronic devices.
The use of electrically conductive polymers has experienced high growth over the past decade, with an increasing growth rate of 6.5 percent projected over the next five years. There are new, advanced conductive polymer applications currently in development that will define opportunities for new value-added plastics.
Let's start by looking at a novel material that enhances medical ultrasound imagery. Conventional ultrasound technology relies on generating images by converting ultrasound waves into electrical signals. Although the technology has advanced throughout the years, it is still largely constrained by bandwidth and sensitivity — obstacles to producing diagnostic-quality images.
Now, a novel metamaterial that converts ultrasound waves into optical signals can provide high-resolution images for biomedical applications.
Scientists at King's College London, in collaboration with colleagues at Texas A&M University, Queen’s University Belfast, and the University of Massachusetts-Lowell, have engineered a material that is not subject to limitations of conventional ultrasound technology, primarily because it converts ultrasound waves into optical signals rather than electrical ones. The optical processing of the signal does not limit the bandwidth or sensitivity of the transducer.
Researchers can go from 0-150 megahertz (MHz) without sacrificing the sensitivity. Current technology typically experiences a substantial decline in sensitivity around 50 MHz. The greater sensitivity enables one to see deeper in tissue, producing visuals in much greater detail than is currently possible.
The metamaterial consists of polypyrrole, a conductive plastic compounded with gold nanorods, generally available in diameters from 10-50 nanometers. An optical signal is sent into the material where it interacts with, and is altered by, incoming ultrasound waves before passing through the material. A detection device then reads the altered optical signal, analyzing the changes in its optical properties to process a higher resolution image.
Experimental Biophysics & Nanotechnology Research Group, King’s College
Fetal ultrasound image (left), optical sensors for ultrasound detection (right)
Next, let's explore conductive polymer in banknote security application development. Integrating memory on banknotes was conceived to demonstrate the feasibility of fabricating active electronic security features, such as radio frequency identification (RFID) tags on banknotes. In theory, an RFID tag would give governments and law enforcement agencies a means to trace money.
Researchers at the King Abdullah University of Science and Technology (KAUST) Functional Nanomaterials and Devices Laboratory, Saudi Arabia have developed the first all-polymer, non-volatile, ferroelectric memory device on a banknote.
Ferroelectric memory is a type of printed memory that relies on a ferroelectric polymer as the active element between electrodes. The banknote memory demonstrated properties that rival those of memories made on conventional silicon substrate. See here for more details.
To make memory devices on banknotes work, all active layers of the device have to be flexible, transparent, inexpensive, capable of being deposited at low process temperatures and robust.
A major challenge is the note's rough fibrous surface, which necessitates adding a planarization layer to make the surface amenable to electrode and active layer deposition. The problem was overcome by applying a smoothing layer of polydimethylsiloxane (PDMS).
In addition to acting as the smoothing or planarizing layer, PDMS provides other important roles, such as providing adhesion and strain isolation for the devices above.
A key feature of the PDMS layer is that it penetrates deep into the fibers of substrates such as banknotes, thereby providing strong adhesion without chemical bonding. By chemically doping the polymer electrode material, its conductivity was dramatically increased, significantly improving performance of the all-polymer ferroelectric memory to a par with metal electrodes.
To ensure adhesion of the highly conducting water based polymer electrodes to the hydrophobic planarization layer, the researchers modified the surface of the planarization layer, using a gentle plasma process that changed the surface properties without losing the smoothness.
Flexible Organic Electronics, Functional Nanomaterials & Devices, King Abdullah University of Science and Technology
Organic electronic multilayering (left), Saudi banknote (right)
The memory devices exhibit excellent performance with low-operating voltages, high mobilities, and a large memory window with excellent retention characteristics. In addition to banknote anticounterfeiting, the memory may find application in inexpensive disposable sensors and RFID tags useful for tracking and transportation of goods, inventory control and vehicle security.
Finally, let’s review the carbon microthread brain-computer interface. Researchers are seeking long-lasting implantable neural electrodes to improve brain-machine interfaces critical for neuroscience research and emerging applications including brain-controlled prosthetic devices that could, for example, allow paraplegics to control robotic limbs, or a computer mouse. Crucial to the problem is development of microelectrodes that record neural activity from the same neurons for years with high fidelity and reliability.
Researchers at the University of Pittsburgh have developed an ultrathin electrode spun from a single carbon fiber that can record neurons in living animals. The "stealthy neural interface," which has the potential to last for 70 years, is made from a single carbon fiber coated with chemicals to make it resistant to proteins in the brain.
The new microthread electrode, approximately 0.007 mm in diameter, is designed to pick up signals from a single neuron as it fires. The electrode is the thinnest yet developed, and about 100 times as thin as the conventional metal electrodes widely used to study animal brains.
Conventional electrodes, stiff and large compared to neurons, are attacked by the immune system and stop recording after several years as scar tissue builds around them. The ultrathin electrodes are unobtrusive, eliciting much reduced chronic reactive tissue response, and therefore do not have these scar tissue issues.
Bio-Integrating Optoelectric Neural Interface & Cybernetics Lab (B.I.O.N.I.C.), University of Pittsburgh
Neural brain network (left), single carbon fiber electrode (center), and demonstration of bending strength of a microthread electrode (right) withstanding substantial bending into a loop-knot without fracturing.
The new neural interface is composed of a single carbon-fiber core, coated with 800 nm of poly(ρ-xylene)6 A dielectric polymer that acts as a dielectric barrier to block out signals from neighboring neurons. A 50 nm thick conductive pad layer of poly(ρ-xylene-4-methyl-2-bromoisobutyrate) at the tip of the thread touches the surface of a single neuron to pick up its signals.
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