Nanomanufacturing: path to implementing nanotechnology

(Nanowerk News) If the promise of nanotechnology is to be fulfilled, then research programs must leapfrog to new nanomanufacturing processes. That’s the conclusion of a review of the current state of nanoscience and nanotechnology to be published in the International Journal of Nanomanufacturing (“Nanomanufacturing: path to implementing nanotechnology”).

Khershed Cooper of the Materials Science and Technology Division, at the Naval Research Laboratory, in Washington, DC and Ralph Wachter of the Division of Computer and Network Systems, at the National Science Foundation, in Arlington, Virginia, USA, explain how research in nanoscience and the emerging applications in nanotechnology have led to new understanding of the properties of matter as well producing many novel materials, structures and devices.

Indeed, the list of possible applications of nanotechnology continues to grow: water filtration and purification, engineered composite materials with modified mechanical properties controlled electrical behaviour and corrosion resistance. There are nano-based materials being used as sealants, anti-fogging and abrasion resistant coatings for glass and other materials, conductive resins, paints and electromagnetic shielding as well as sensors, self-healing materials, super-hydrophobic surfaces, solar cells and ultracapacitors for energy storage as well as materials for armour and protection against bullets and bombs.

The team’s own research has focused on developing tools and techniques to make scalable processes for nanomanufacturing. They are investigating massively parallel techniques, masks and maskless processes for making 3D structures with nanoscopic features. However, they also suggest that several obstacles must be surmounted for nanotechnology to thrive as a future industrial endeavour. In particular, the team believes that research and development should be directed in the following areas:

– Multi-scale design, modelling and simulation of nanosystems. – Component integration within large-scale systems. – Integration across physical scales. – Qualification, certification, verification and validation. – Cyber-enabled manufacturing systems.

“Looking ahead, nanotechnology is slated to move into complex, multi-functional, multi-component nanosystems, e.g., nano-machines and nano-robots,” the team concludes. “These nanosystems will be adaptive, responsive to external stimuli, biomimetic, intelligent, smart and autonomous. Nanomanufacturing R&D will be needed to develop the knowledge base for the reliable production of these complex nanosystems.”

Source: Inderscience

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DOE: Mixing Nanoparticles to Make “Multifunctional” Materials

Posted: Oct 20, 2013

Mixing nanoparticles to make multifunctional materials

(Nanowerk News) Scientists at the U.S. Department of Energy‘s Brookhaven National Laboratory have developed a general approach for combining different types of nanoparticles to produce large-scale composite materials.

The technique, described in a paper published online by Nature Nanotechnology on October 20, 2013 (“A general strategy for the DNA-mediated self-assembly of functional nanoparticles into heterogeneous systems”), opens many opportunities for mixing and matching particles with different magnetic, optical, or chemical properties to form new, multifunctional materials or materials with enhanced performance for a wide range of potential applications.

The approach takes advantage of the attractive pairing of complementary strands of synthetic DNA-based on the molecule that carries the genetic code in its sequence of matched bases known by the letters A, T, G, and C.

After coating the nanoparticles with a chemically standardized “construction platform” and adding extender molecules to which DNA can easily bind, the scientists attach complementary lab-designed DNA strands to the two different kinds of nanoparticles they want to link up. The natural pairing of the matching strands then “self-assembles” the particles into a three-dimensional array consisting of billions of particles. Varying the length of the DNA linkers, their surface density on particles, and other factors gives scientists the ability to control and optimize different types of newly formed materials and their properties.

DNA linkers allow different kinds of nanoparticles to self-assemble and form relatively large-scale nanocomposite arrays. This approach allows for mixing and matching components for the design of multifunctional materials.

“Our study demonstrates that DNA-driven assembly methods enable the by-design creation of large-scale ‘superlattice’ nanocomposites from a broad range of nanocomponents now available-including magnetic, catalytic, and fluorescent nanoparticles,” said Brookhaven physicist Oleg Gang, who led the research at the Lab’s Center for Functional Nanomaterials (CFN). “This advance builds on our previous work with simpler systems, where we demonstrated that pairing nanoparticles with different functions can affect the individual particles’ performance, and it offers routes for the fabrication of new materials with combined, enhanced, or even brand new functions.”

Future applications could include quantum dots whose glowing fluorescence can be controlled by an external magnetic field for new kinds of switches or sensors; gold nanoparticles that synergistically enhance the brightness of quantum dots’ fluorescent glow; or catalytic nanomaterials that absorb the “poisons” that normally degrade their performance, Gang said.

“Modern nano-synthesis methods provide scientists with diverse types of nanoparticles from a wide range of atomic elements,” said Yugang Zhang, first author of the paper. “With our approach, scientists can explore pairings of these particles in a rational way.”

Pairing up dissimilar particles presents many challenges the scientists investigated in the work leading to this paper. To understand the fundamental aspects of various newly formed materials they used a wide range of techniques, including x-ray scattering studies at Brookhaven’s National Synchrotron Light Source (NSLS) and spectroscopy and electron microcopy at the CFN.

For example, the scientists explored the effect of particle shape. “In principle, differently shaped particles don’t want to coexist in one lattice,” said Gang. “They either tend to separate into different phases like oil and water refusing to mix or form disordered structures.”

The scientists discovered that DNA not only helps the particles mix, but it can also improve order for such systems when a thicker DNA shell around the particles is used.

They also investigated how the DNA-pairing mechanism and other intrinsic physical forces, such as magnetic attraction among particles, might compete during the assembly process.

For example, magnetic particles tend to clump to form aggregates that can hinder the binding of DNA from another type of particle. “We show that shorter DNA strands are more effective at competing against magnetic attraction,” Gang said.

For the particular composite of gold and magnetic nanoparticles they created, the scientists discovered that applying an external magnetic field could “switch” the material’s phase and affect the ordering of the particles.

“This was just a demonstration that it can be done, but it could have an application-perhaps magnetic switches, or materials that might be able to change shape on demand,” said Zhang.

DNA linkers allow different kinds of nanoparticles to self-assemble and form  relatively large-scale nanocomposite arrays. This approach allows for mixing and  matching components for the design of multifunctional materials.

The third fundamental factor the scientists explored was how the particles were ordered in the superlattice arrays: Does one type of particle always occupy the same position relative to the other type-like boys and girls sitting in alternating seats in a movie theater-or are they interspersed more randomly?

“This is what we call a compositional order, which is important for example for quantum dots because their optical properties-e.g., their ability to glow-depend on how many gold nanoparticles are in the surrounding environment,” said Gang. “If you have compositional disorder, the optical properties would be different.” In the experiments, increasing the thickness of the soft DNA shells around the particles increased compositional disorder.

These fundamental principles give scientists a framework for designing new materials. The specific conditions required for a particular application will be dependent on the particles being used, Zhang emphasized, but the general assembly approach would be the same.

Said Gang, “We can vary the lengths of the DNA strands to change the distance between particles from about 10 nanometers to under 100 nanometers-which is important for applications because many optical, magnetic, and other properties of nanoparticles depend on the positioning at this scale. We are excited by the avenues this research opens up in terms of future directions for engineering novel classes of materials that exploit collective effects and multifunctionality.”

Source: Brookhaven National Laboratory

 

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Physicists at CU (Boulder, CO) create ‘recipe book’ for building new materials

(Nanowerk News) By showing that tiny particles injected  into a liquid crystal medium adhere to existing mathematical theorems,  physicists at the University of Colorado Boulder have opened the door for the  creation of a host of new materials with properties that do not exist in nature.

The findings show that researchers can create a “recipe book” to  build new materials of sorts using topology, a major mathematical field that  describes the properties that do not change when an object is stretched, bent or  otherwise “continuously deformed.” Published online Dec. 23 in the journal Nature (“Topological colloids”, the study also is the  first to experimentally show that some of the most important topological  theorems hold up in the real material world, said CU-Boulder physics department  Assistant Professor Ivan Smalyukh, a study senior author.

This  image shows polarized light interacting with a particle injected into a liquid  crystal medium. (Image: Bohdan Senyuk and Ivan Smalyukh, Colorado University)

The research could lead to upgrades in liquid crystal displays,  like those used in laptops and television screens, to allow them to interact  with light in new and different ways. One possibility is to create liquid  crystal displays that are even more energy efficient, Smalyukh said, extending  the battery life for the devices they’re attached to.

The research was funded in part by Smalyukh’s Presidential Early  Career Award for Scientists and Engineers, which he received from President  Barack Obama in 2010. And the research supports the goals laid out by the White  House’s Materials Genome Initiative, Smalyukh said, which seeks to deploy “new  advanced materials at least twice as fast as possible today, at a fraction of  the cost.”

Smalyukh, postdoctoral researcher Bohdan Senyuk, and doctoral  student Qingkun Liu set up the experiment by creating colloids — solutions in  which tiny particles are dispersed, but not dissolved, throughout a host medium.  Colloids are common in everyday life and include substances such as milk, jelly,  paint, smoke, fog and shaving cream.

For this study, the physicists created a colloid by injecting  tiny particles into a liquid crystal — a substance that behaves somewhat like a  liquid and somewhat like a solid. The researchers injected differently shaped  particles that represent fundamental building-block shapes in topology. That  means each of the particles is distinct from the others and one cannot be turned  into the other without cutting or gluing. Objects that look differently can  still be considered the same in topology if one can be turned into the other by  stretching or bending – types of “continuous deformations.”

In the field of topology, for example, an object shaped like a  donut and an object shaped like a coffee cup are treated the same. That’s  because a donut shape can be “continuously deformed” into a coffee cup by  indenting one side of the donut. But a donut-shaped object cannot be turned into  a sphere or a cylinder because the hole in the donut would have to be eliminated  by “gluing” the sides of the donut back together or by “cutting” the side of the  donut.

Once injected into a liquid crystal, the particles behaved as  predicted by topology. “Our study shows that interaction between particles and  molecular alignment in liquid crystals follows the predictions of topological  theorems, making it possible to use these theorems in designing new composite  materials with unique properties that cannot be encountered in nature or  synthesized by chemists,” Smalyukh said. “These findings lay the groundwork for  new applications in experimental studies of low-dimensional topology, with  important potential ramifications for many branches of science and technology.”

Source: University of Colorado  Boulder

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The potentially world-changing research that no one knows about

 

Imagine that there exists a two-dimensional (single-layer) crystal that is made of a commonly available element, is stronger than steel yet lighter weight and flexible, displays ballistic electron mobility (for comparison, two orders of magnitude greater mobility than silicon, at room temperature), and is sufficiently optically active to see with the naked eye (though far more practically, using an optical microscope). Prospective applications include flexible, high-speed electronic devices and new composite materials for aircraft.

 

Would this sound like a potentially world-changing substance worthy of scientific attention and funding?

That substance is graphene, a single layer of graphite with hexagonally arranged carbon atoms (visualized as chicken wire).

 

Now imagine that the mechanical properties of this substance aren’t measured yet, as was the case for graphene before 2009. Imagine further that there is no way to grow or isolate the single-layer crystals in their free state, as was the case for graphene before 2004. Stepping back in time yet further, imagine that the theoretical work predicting massless charge carrier behavior hasn’t been carried out yet, as was the case for graphene before 1984.

 

Peeling back these milestones, we can see that if the scientific question being asked is “What can be realized from here?” then the graphene timeline played out characteristically, with major advancements coming primarily from opportunity-based research. In other words, over 50+ years, from the initial theoretical work on graphene in 1947 until stable monolayers were achieved in 2004, there was limited vision of what end-goals might be achievable and limited drive to get there.

 

What happens when a different question is asked, specifically “What can be realized according to physical law?” This is the key premise of the exploratory engineering approach, a methodology proposed by Eric Drexler for assessing the capabilities of future technologies. He points out, for example, that the principles of space flight had been worked out long before science and industry advanced enough to get to actual launch.

 

For initial space flight development, the answers to the two questions above were dramatically different: what could be done in practice was far behind what had been established as theoretically possible, and there was no defined path between them. By identifying what was achievable according to physical law, the longer-term goal of space flight entered the consciousness of physicists, engineers, and politicians, bringing great minds and great resources to the challenge.

 

With the benefit of similarly future-focused knowledge, perhaps graphene might have received far more attention far sooner. Consider this: the groundbreaking experimental work that sparked the field as we know it today was the discovery that single-layer graphene could be extracted from a piece of graphite by (essentially) pressing cellophane tape against it and peeling it away. In other words, a decades-long roadblock to achievements in graphene research was not a matter of inadequate supporting technology but one of limited scientific attention.

 

Here graphene serves as a useful illustration of how progress could potentially be hindered when opportunity-based research is relied upon exclusively. Scientific advancement could benefit significantly from deliberate, exploratory engineering. Perhaps there are numerous other ‘graphenes’ right now, going unnoticed or under-prioritized, because we are failing to ask: what can be realized according to physical law?