For close to two decades, Cornell scientists have developed processes for using polymers to self-assemble inorganic nanoparticles into porous structures that could revolutionize electronics, energy and more.
This process has now been driven to an unprecedented level of precision using metal nanoparticles, and is supported by rigorous analysis of the theoretical details behind why and how these particles assemble with polymers. Such a deep understanding of the complex interplay between the chemistry and physics that drive complex self-assembly paves the way for these new materials to enter many applications, from electrocatalysis in fuel cells to voltage conductance in circuits.
A: A schematic of the block copolymer synthesis method which includes gold and platinum nanoparticle self-assembly. B. Molecular structure of the block copolymer used. C. Molecular structure of stabilizing ligands attached to gold and …more
Ulrich Wiesner, the Spencer T. Olin Professor of Materials Science and Engineering, led what is probably the most comprehensive study to date of block copolymer nanoparticle self-assembly processes. The study was published online Feb. 21 in Nature Communications.
From the outside, the process looks simple enough. Begin with platinum and gold particles that grow from a precursor. A chemical called a ligand coats the particles and precisely controls their size. Add to this designed molecules called block copolymers – long chains of two or three organic materials. The polymers combine with the platinum and gold nanoparticles, all of which assemble into ordered, cubic, three-dimensional structures. Etch away the polymer, and what’s left are scores of nanoparticles forming porous 3-D cubic networks.
Each step – from the exact structure of the ligands, to the synthesis of the polymers – requires precise chemistry and detailed understanding of each material’s role. The Nature Communications analysis drew on the expertise of collaborators in electron tomography, energy dispersive microscopy and percolation theory. For example, collaborators from the Japan Science and Technology Agency used electron tomography to map the location of every single particle in the samples, which then could be compared with theoretical predictions. The result is a comprehensive set of design criteria that could lead to readying these particle networks for larger scale solution processing.
“Not only can we make these materials, but through electron tomography in particular, we can analyze these structures at a depth that just has not been done before,” Wiesner said. “The comparison with theory allows us to fully understand the physical mechanisms by which these structures are formed.”
Why pay such attention to these self-assembled nanoparticle networks? They’re made in a way that would never happen in nature or by conventional laboratory means. They are uniformly porous with high surface area and, therefore, are highly catalytic and potentially useful for energy applications.
Perhaps best of all, working with polymers means cost-effective, large-scale processing could be a snap.
Several decades of polymer science has given the world efficient scalability unsurpassed in the materials world – think plastics production. Wiesner and colleagues have proven the concept of self-assembled metal nanoparticles using block copolymer-based solution processing that goes beyond the “glass vial in a lab,” Wiesner said.
“Now that we understand how it all works, our process lends itself easily to larger-scale production of such materials,” he said.
Conductive nanomaterials for printed electronics applications
By Michael Berger. Copyright © Nanowerk
(Nanowerk Spotlight) The term printed electronics refers to the application of printing technologies for the fabrication of electronic circuits and devices, increasingly on flexible plastic or paper substrates. Printed electronics has its origins in conductive patterns printed as part of conventional electronics, forming flexible keyboards, antennas and so on.
Then came fully printed testers on batteries, electronic skin patches and other devices made entirely by printing, including batteries and displays (read more: “Printed electronics widens its scope”). Traditionally, electronic devices are mainly manufactured by photolithography, vacuum deposition, and electroless plating processes. In contrast to these multistaged, expensive, and wasteful methods, inkjet printing offers a rapid and cheap way of printing electrical circuits with commodity inkjet printers and off-the-shelf materials.
All inkjet technologies are based on digitally controlled generation and ejection of drops of liquid inks using one of two different modes of operation: continuous and drop-on-demand printing. Conductive inkjet ink is a multi-component system that contains a conducting material in a liquid vehicle (aqueous or organic) and various additives (such as rheology and surface tension modifiers, humectants, binders and defoamers) that enable optimal performance of the whole system, including the printing device and the substrate. The conductive material may be dispersed nanoparticles, a dissolved organometallic compound, or a conductive polymer.
A review article in Small (“Conductive Nanomaterials for Printed Electronics”) by Alexander Kamyshny and Shlomo Magdassi from The Hebrew University of Jerusalem, provides a state-of-the-art overview of the synthesis of metal nanoparticles; preparation of stable dispersions of metal nanoparticles, carbon nanotubes (CNTs) and graphene sheets; ink formulations based on these dispersions, sintering of metallic printed patterns for obtaining high electrical conductivity; and recent progress in the utilization of metal nanoparticles, carbon nanotubes, and graphene for the fabrication of various functional devices.
Requirements and challenges for printable dispersions of conductive nanomaterials The use of nanomaterials for the formulation of conductive inkjet inks poses several challenges:
- – the nanoparticles in the ink should be stable against aggregation and precipitation in order to provide reproducible performance
- – nanoparticle-based conductive inks should provide good electrical conductivity of printed patterns
- – there is a need need for a post-printing process in order to sinter the nanoparticles for obtaining continuous metallic phase, with numerous percolation paths between metal particles within the printed patterns
- – when using carbon nanotubes or graphene, the challenge is to prevent aggregation into CNT bundles or graphene layers.
In their article, Kamyshny and Magdassi address these challenges in great detail and then go on to describe preparation methods for metal, graphene, and CNT-based inkjet inks, which are suitable for printed electronics, and post-printing processing methods for obtaining high electrical conductivities.
Printing of a conductive 3D structure with the use of ink composed of an UV-curable emulsion and a dispersion of metal nanoparticles. Inset is a 3D profile of a 200 µm width lines composed of 1, 3, 6, 10, and 20 printed layers.(© The Royal Society of Chemistry)
Applications of conductive nanomaterials The authors also discuss several applications of conductive nanomaterials for the fabrication of printed electronic devices. This includes fabrication and properties of transparent conductive electrodes, which are nowadays essential features for many optoelectronic devices, and inkjet-printed devices, such as RFID tags, light emitting devices, thin-film transistors (TFTs) and solar cells.
Transparent electrodes The market for transparent electrodes has grown tremendously due to wide proliferation of LCD displays, touch screens, thin-film solar cells, and light emitting devices. The most widely used material is indium tin oxide (ITO) with a market share of more than 97% of transparent conducting coatings. ITO coatings have some major drawbacks, though, and many efforts to find alternatives are based on nanomaterials – metal nanoparticles, metal nanowires, carbon nanotubes, and graphene – which can be printed directly on various substrates without etching processes.
RFID tags The main elements of an RFID (Radio Frequency Identification) tag are a silicon microchip and an antenna, which provide power to the tag and are responsible for communication with a reading device. Direct inkjet printing of antennas on plastic and paper substrates with the use of metal nanoparticles inks is a promising approach to the production of low-cost RFID tags.
Thin-film transistors Conductive nanomaterials are used to produce the conductive features on both inorganic and organic TFTs. See for instance our recent Nanowerk Spotlight on inkjet printing of graphene for flexible electronics or the report on inkjet printing of single-crystal films of organic semiconductors.
Light-emitting devices Light emitting devices (or electroluminescent devices, ELDs) are composed of a semiconductor layer placed between two electrodes, and emit light in response to electric current. LEDs to be used for lighting, require a highly conductive grid (“shunting lines”) for homogeneous distribution of current around the lighting device. These circuits can be fabricated on various substrates including plastic, by various printing processes using conductive nanomaterials.
Solar cells The first demonstration of inkjet-printed solar cells was already made in 2007 using fullerene-based ink. The results were discussed in this paper: “High Photovoltaic Performance of Inkjet Printed Polymer:Fullerene Blends”. In recent years, metal nanoparticles as well as nanowires and CNTs have been also used in solar cells fabrication as well.
Concluding their review, the authors note that, in spite of the remarkable scientific progress in preparation processes and applications of conductive nanomaterials, they are still not widely used by the industry in significant quantities:
“The current high price of commercially available inks, which are based mainly on the high cost silver, impedes their wide use for large area printed electronics. Therefore, research should be focused on the development of new nanomaterials and ink formulations based on low cost metals with high electrical conductivity such as copper, nickel, and aluminum.”
They also note that in recent years, many scientific activities have been focusing on graphene and that we can expect future developments in printed electronics that will combine CNTs with graphene. Successive utilization of graphene for printed electronics requires ink formulations with high graphene loading, which are stable against flakes aggregation.
One final thought is the application of conductive nanomaterials in 3D printing of conductive patterns which opens some important perspectives for materials science. Although, this field is at its very early stages of research and development, and the search for new nanomaterials as well as suitable 3D fabrication tools based on wet deposition, it is a stimulating challenge for materials scientists.
25 Feb 2014
A team of UConn chemists has discovered a new way of making a class of porous materials that allows for greater manufacturing controls and has significantly broader applications than the longtime industry standard.
The process, more than three years in the making, has resulted in the creation of more than 60 new families of materials so far, with the potential for many more. The key catalyst in the process is recyclable, making it a ‘green’ technology.
“This is definitely the most exciting project I’ve been involved in over the past 30 years,” says Board of Trustees Distinguished Professor Steven L. Suib, the project’s principal investigator.
The research team’s novel process creates monomodal mesoporous metal oxides using transition metals such as manganese, cobalt, and iron. The mesopores are between 2 and 50 nanometers in diameter and are evenly distributed across the material’s surface.
UConn’s scientists used nitric oxide chemistry to change the diameter of the pores. This unique approach helped contain chemical reactions and provided unprecedented control and flexibility.
Having materials with uniform microscopic pores allows targeted molecules of a particular size to flow into and out of the material, which is important in such applications as adsorption, sensors, optics, magnetic, and energy products such as the catalysts found in fuel cells.
“When people think about these materials, they think about lock-and-key systems,” says Suib. “With certain enzymes, you have to have pores of a certain size and shape. With this process, you can now make a receptacle for specific proteins or enzymes so that they can enter the pores and specifically bind and react. That’s the hope, to be able to make a pore that will allow such materials to fit, to be able to make a pore that a scientist needs.”
UConn’s chemists replaced a long-standing water-based process with one employing a synthetic chemical surfactant to create the mesopores. By reducing the use of water, adding the surfactant, then subjecting the resulting nanoparticles to heat, the research team found that it could generate thermally-controlled, thermally-stable, uniform mesoporous materials with very strong crystalline walls. The mesopores, Suib says, are created by the gaps that are formed between the organized nanoparticles when they cluster together. The team found that the size of those gaps or pores could be tailored – increased or decreased – by adjusting the nanostructure’s exposure to heat, a major advancement in the synthesis process.
“Such control of pore-size distribution, enhanced pore volumes, and thermal stabilities is unprecedented …,” the team wrote in its report.
The UConn team found that the process could be successfully applied to a wide variety of elements of the periodic table. Also, the surfactant used in the synthesis is recyclable and can be reused after it is extracted with no harm to the final product.
“We developed more than 60 families of materials,” says Suib. “For every single material we made, you can make dozens of others like it. You can dope them by adding small amounts of impurities. You can alter their properties. You can make sulfides in addition to oxides. There is a lot more research that needs to be done.”
Washington, Feb 24 (IANS) Scientists have developed a new system that can precisely deliver anti-inflammatory drugs to immune cells gone out of control, while sparing their well-behaved counterparts.
The findings by researchers at the University of Illinois at Chicago were published online Feb 23 in Nature Nanotechnology.
The system uses nanoparticles made of tiny bits of protein designed to bind to unique receptors found only on neutrophils, a type of immune cell engaged in detrimental acute and chronic inflammatory responses.
In a normal immune response, neutrophils circulating in the blood respond to signals given off by injured or damaged blood vessels and begin to accumulate at the injury, where they engulf bacteria or debris from injured tissue that might cause infection.
In chronic inflammation, neutrophils can pile up at the site of injury, sticking to the blood vessel walls and to each other and contributing to tissue damage, reported Science Daily.
Corticosteroids and non-steroidal anti-inflammatory drugs used to treat inflammatory diseases are “blunt instruments that affect the whole body and carry some significant side effects”, said Asrar B. Malik, Schweppe Family Distinguished Professor and head of pharmacology in the UIC College of Medicine.
Malik is also lead author of the paper.
“The nanoparticle is very much like a Trojan horse,” Malik said. “It binds to a receptor found only on these activated, sticky neutrophils, and the cell automatically engulfs whatever binds there. Because circulating neutrophils lack these receptors, the system is incredibly precise and targets only those immune cells that are actively contributing to inflammatory disease.”
Malik said, the findings “show that nanoparticles can be used to deliver drugs in a highly targeted, specific fashion to activated immune cells and could be designed to treat a broad range of inflammatory diseases”.
With more than $1.5 billion in new research funding, budget 2014 addresses the increasing need for Canada’s research-intensive universities to compete on the world stage and attract and develop top-level research talent vital to Canada’s future prosperity.
“I am thrilled with the Government of Canada’s strong commitment to Canadian universities through budget 2014. This budget represents a visionary investment in research excellence and innovation that will ensure Canada remains competitive globally,” said Samarasekera. “This funding will allow the U of A and our peers to attract the best and brightest to advance the scientific discoveries, solutions and ideas that will benefit Canadians for generations to come.”
Samarasekera congratulates the Government of Canada for this bold investment to help position Canadian universities in a global environment, including $1.5 billion over 10 years to create the Canada First Research Excellence Fund. The university also thanks the federal government for its enhanced funding support through Tri-Council funding agencies.
The CFREF program, put forwarded with the support of both the U15 Group of Canadian Research Universities and the Association of Universities and Colleges of Canada, is essential for Canada to achieve global leadership in specific fields, attract talent and advance the country’s research standing in the world, she said.
“In a time of budget austerity, I am particularly delighted by the Government of Canada’s funding commitment to the country’s universities and ensuring Canada remains a true world leader in higher education, research and innovation.”
• $1.6 billion over five years in new support for research and innovation
• $1.5 billion over 10 years to create the Canada First Research Excellence Fund, including: $50 million in 2015–16, $100 million in 2016–17, $150 million in 2017–18, $200 million in 2018–19 and beyond.
• An additional $46 million per year on an ongoing basis to the granting councils in support of advanced research and scientific discoveries, including the indirect costs of research.
• $15 million per year to the Canadian Institutes of Health Research, for the expansion of the Strategy for Patient-Oriented Research, the creation of the Canadian Consortium on Neurodegeneration in Aging and other health research priorities.
• $15 million per year to the Natural Sciences and Engineering Research Council, to support advanced research in the natural sciences and engineering.
• $7 million per year for the Social Sciences and Humanities Research Council, to support advanced research in the social sciences and humanities.
• $9 million per year for the Indirect Costs Program
“Genesis Nanotechnology .. Great Things from Small Things!”
– See more at: http://news.ualberta.ca/newsarticles/2014/february/2014-federal-budget?utm_source=Daily%20News%20Email&utm_medium=email&utm_campaign=Daily%20News:%20February%2012,%202014&utm_content=889250#sthash.nniriUF6.dpuf
12 Feb 2014
Published on Feb 11, 2014
The resources needed to support a future global population of more than nine billion people requires near-term action. At Lockheed Martin, we are in the business of protecting nations and providing vital citizen services; we are also in the business of engineering solutions to protect our planet.
10 Feb 2014
|Source: Fraunhofer Society|
By Michael Berger. Copyright © Nanowerk
(Nanowerk Spotlight) Fabrication of three-dimensional (3D) objects through direct deposition of functional materials – also called additive manufacturing – has been a subject of intense study in the area of macroscale manufacturing for several decades.
These 3D printing techniques are reaching a stage where desired products and structures can be made independent of the complexity of their shapes – even bioprinting tissue is now in the realm of the possible. Applying 3D printing concepts to nanotechnology could bring similar advantages to nanofabrication – speed, less waste, economic viability – than it is expected to bring to manufacturing technologies.
In addition, pre-patterned micro- or nanostructures could be used as substrates, allowing researchers to realize unprecedented manufacturing flexibility, functionality and complexity at the nanoscale. Researchers in Korea have now shown that nanoscale 3D objects such as free-standing nanowalls can by constructed by an additive manufacturing scheme. Even without the motion of the substrate, nanojets are spontaneously laid down and piled to yield nanowalls. The team, led by Ho-Young Kim, a professor at Seoul National University, has published their findings in the January 28, 2014 online edition of Langmuir (“Toward Nanoscale Three-Dimensional Printing: Nanowalls Built of Electrospun Nanofibers”).
(Schematic of the experimental apparatus. (Reprinted with permission from American Chemical Society)
“Electrospinning that produces polymer nanojets is a relatively simple and inexpensive method to yield nanoscale fibers, but the fiber streams are so chaotic that control of individual fibers has been considered almost impossible,” Kim explains to Nanowerk. “In our recent work, we have shown that an electrospun polymer solution jet, which tends to become unstable as traveling in the air due to Coulombic repulsion, can be stably focused onto a thin metal electrode line.” Kim and his team also elucidated the fundamental electromechanical mechanism that enables the spontaneous stacking of a nanofiber onto itself to provide a physical basis behind this novel nanofabrication process.
In this novel method, a thin metal line on an insulating plate strongly focuses the electrical field, thus the whipping instability of the electrical nanojets is suppressed. To stack the fibers in a controlled fashion, the researchers manipulate the fiber deposit into attracting the incoming nanojets rather than repelling them by draining the electrical charge quickly. Then they get a nanowall that lines the ground, implying that various free-standing structures can be created by patterning the microscale ground lines in a desired shape.
Nanowall built on a stationary metal line. Top: Illustration of the deposition of a nanofiber to yield a free-standing nanowall. Bottom left: SEM (scanning electron microscopy) images of the free-standing nanowall. Bottom right: SEM image of the end of the nanowall that resembles a racket. (Reprinted with permission from American Chemical Society)
The construction of a free-standing nanowall is the most fundamental step to achieve 3D nanoprinting. This process is so attractive because it needs only a power supply and a linear stage to build free-standing nanowalls after drawing metal microlines, all of which can be conducted under normal laboratory conditions.
Kim points out that this technique has a significant economic advantage as compared to conventional nanomanufacturing processes used to build nanowalls such as DRIE (deep reactive ion etching). The current scheme of repeatedly stacking nanofibers onto a conducting line is suited for fabricating nanoelectrodes consisting of straight walls and nanochannel field effect transistors (FETs) utilizing insulating nanowalls as gaps of metal patterns. Further sophisticated methods to control the nanojets have the potential to realize rapid 3D printing of complicated shapes, which can be used for bio scaffolds, nanofilters and even nanorobots.
However, further developments, such as lowering the nanojet speed and positioning the target place with high precision, are necessary to make the current focused electrojetting process fully capable of 3D printing of complicated shapes. “Full 3D control of an electrospun nanojet would possibly revolutionize the current nanofabrication technology, which we aim to achieve in the long run,” says Kim. “However, we believe that such great achievement cannot be made with a single step. Further development for the precise control of the nanojet could realize full 3D nanofabrication.”
By Michael Berger. Copyright © Nanowerk
(Nanowerk Spotlight) A field effect transistor (FET) is a type of transistor that relies on an electric field to control the shape and hence the conductivity of a ‘channel’ in a semiconductor material. Several years ago, it was shown in a series of experiments that a silicon nanowire can be used as the source-drain channel in FETs.
Subsequently, it was shown that these nanowire field-effect sensors show significant advantages of real-time, label-free and highly sensitive detection of a wide range of analytes in liquid phase, including proteins, nucleic acids, small molecules, and viruses in single-element or multiplexed formats (read more: “Amplifying biomolecular signals with nanoscale field effect transistors”).
“In contrast to the liquid phase, it has been a challenge to obtain selective silicon nanowire field effect transistor (SiNW FET) sensors for gaseous chemical species, such as, volatile organic compounds (VOCs) that are associated with environmental pollution, quality control, explosive materials, or various diseases,” says Hossam Haick, a professor in the Department of Chemical Engineering and Russell Berrie Nanotechnology Institute at Technion – Israel Institute of Technology.
Over the years, Haick’s Laboratory for Nanomaterial Based Devices has worked on the detection of cancer-related VOCs and breath samples using E-noses based on gold nanoparticle and carbon nanotube chemresistors (see our previous Nanowerk Spotlight on this work: “Nanotechnology sensor can ‘smell’ lung cancer in exhaled breath”). “Motivated by the unique features of the SiNW FET sensors and the ease to integrate these sensors in the currently available VLSI technology, we tried to use molecularly modified SiNW FETs to detect VOCs,” Haick tells Nanowerk. “We found that one SiNW FET sensor could provide multiple sensing signals towards VOCs. Further, we noticed that the multiple sensing character of one SiNW FET was similar as that of a sensor array.
Thus, the concept of E-nose can rely on one SiNW FET sensor to selectively detect VOCs.” This work, which has been reported in the January 17, 2014 online edition of Nano Letters (“Artificial Sensing Intelligence with Silicon Nanowires for Ultraselective Detection in the Gas Phase”), is based on the electronic nose (E-nose) concept – electronic devices which mimic the olfactory systems of mammals and insects.
Scheme of a molecularly modified SiNW FET sensor (Reprinted with permission from American Chemical Society)
The selectivity of E-noses towards analytes are achieved by analyzing sets of sensing signals using pattern recognition methods, rather than selectively adsorbing analyte on sensor site (‘lock-and-key’ approach). “In traditional E-noses, sensor arrays are always used to generate fingerprint patterns for analytes,” explains Haick.
“However, in our study, the applied E-noses contain one sensor only, but they are able to identify many kinds of analytes.” He adds that the use of one FET sensor in an E-nose can minimize the device size, decrease the power consumption, and simplify the device circuitry and related computation parts.
The approach relies on the use of multiple independent parameters of a specific molecularly modified SiNW FET (e.g., voltage threshold, hole mobility, subthreshold swing) as input for artificial neural network (ANN) models, which, in turn, can be trained in its ensemble to make the targeted detection. This means that, relying on the raw responses of each SiNW FET sensor, ANN models are employed to seek selectivity toward specific VOCs.
The researchers say that the artificial sensing intelligence with SiNW FETs can be applied in environmental monitoring and disease diagnosis in the gas phase. In addition, this approach can be applied in other FET based sensor applications to selectively detect analytes in both gas and liquid phase.
Haick points out that this work and the underlying research combine two areas: sensor design and pattern recognition algorithms. “For the sensor design, developing SiNW FET sensors with high sensitivity, fast response, and longtime stability is required towards various real world applications. For the pattern recognition algorithm, developing and optimizing algorithms to decrease the data processing time consumption, increase the prediction accuracy, and increase the ability to treat sensing data obtained in complex system like multi VOC mixtures, are required and of great importance.” “Efficient combination of sensor designing and pattern recognition algorithm is the key, and also a great challenge, for the future artificial sensing intelligence sensor research,” he concludes.