Yesterday I bent over in the attempt to tie the absurdly bright purple shoe laces on my almost offensively bright purple sneakers and made a startling discovery: I’m not as flexible as I used to be.  In fact, the overwhelming tightness of my hamstrings makes your standard British upper lip look positively floppy; and as I fired up my smartphone to schedule some emergency yoga I was reminded that I had yet to share an amazing new fully stretchable OLED display recently developed at the University of California, Los Angeles, a place where they know a thing or two about screens.

OLEDs or Organic Light-Emitting Diodes are great technology for screens primarily because they work without a backlight and can display deep black levels for high contrast.  OLED displays can be manufactured thinner and lighter than liquid crystal displays (LCDs) and “in low ambient light conditions such as dark rooms an OLED screen can achieve a higher contrast ratio than an LCD, whether the LCD uses either cold cathode fluorescent lamps or the more recently developed LED backlight. Due to their low thermal conductivity, they typically emit less light per area than inorganic LEDs” (Source: Wikipedia). What it all boils down to is that OLEDs are the bees knees. FACT.

Image courtesy wired.com

Once researchers saw how thin they could make OLEDs it was only a matter of time before people starting thinking about how to make them flexible. Stretchable electronics open up a world where video displays get rolled up and stuffed in your pocket, electronic sheets drape like cloth, electronics grow and shrink on command, and the mighty condor gets taken off the endangered species list.

Early attempts at stretchable electronics resulted in prototypes that connected rigid LEDs with stretchable material and others that bent but couldn’t stretch. The challenge researchers faced was how to ensure that the electrode could maintain connectivity while being deformed since many conductive materials can’t stretch nearly as far as one might like.  Enter the humble yet versatile carbon nanotube: it’s stretchable, conductive, appears transparent in thin layers, and it usually picks up the check after lunch dates.

The fly in the nanotube ointment, so to speak, is the fact that carbon nanotubes must be attached to a surface; the attachment can be tricky to pull off since when applied to a plastic backing nanotubes have a tendency to slide off or even slide past each other when the backing is stretched. To evict said proverbial fly from said proverbial ointment, the UCLA researchers created a carbon nanotube and polymer electrode layered on a stretchable, light-emitting plastic.

The researchers “coated carbon nanotubes onto a glass backing and added a liquid polymer that becomes solid yet stretchable when exposed to ultraviolet light. The polymer diffuses throughout the carbon nanotube network and dries to a flexible plastic that completely surrounds the network rather than just resting alongside it. Peeling the polymer-and-carbon-nanotube mix off of the glass yields a smooth, stretchable, transparent electrode” (Grifantini).  I imagine that the carbon nanotubes embedded in the plastic stretch at roughly the same rate, and that the plastic keeps to itself mostly and doesn’t interfere with the ability of the nanotubes to conduct electricity.

Image courtesy pcworld.com

The team sandwiched two layers of carbon nanotube electrode around another plastic that emits light when current runs through it.  Researchers obtained a laminator from a local office supply store to press the layered device together so that it could be handled safely in the presence of electric current.  As an aside, we did the same thing when we screen printed an electroluminescent lamp in Switzerland this summer and were hoping to not get electroshocked by the circuits. (More on that soon).  In contrast to our electroluminescent display, the flexible OLED created by the UCLA team can be stretched by as much as 45 percent while emitting a colored light.

Their prototype is a two-centimeter square that emits a one-centimeter square brilliant sky-blue light that stretches like silly putty until it loses conductivity due to being stretched too far or too many times (Grifantini).  The researchers also made a prototype using silver nano wires (which are more conductive than nanotubes) that exhibits similar stretching properties but is even more conductive.  Their layered approach is a great idea, not least because it’s easy to imagine how the process could be scaled up for production.  Now if only those scientists could help me with my hamstrings….

WU XING:

I have filed stretchable OLEDs under Water, Wood and Fire because they’re flexible, stretchy, and they light up.

Cited:

Grifantini, Kristina. “The First Fully Stretchable OLED.” Techreview.com 08/26/11. Accessed 10/05/11. URL.

Watch video: Stretchable OLED – Tech Review

Similar issues arise in the making of structural materials such as metals and alloys. The materials properties are set once and for all during production. This forces engineers to make compromises in the selection of the mechanical properties of a material. Greater strength is inevitably accompanied by increased brittleness and a reduction of the damage tolerance.”

Image courtesy Technical University of Hamburg and the Helmholtz Center Geesthacht

Jörg Weißmüller, a materials scientist at both the Technical University of Hamburg and the Helmholtz Center Geesthacht, and his team wondered if you could switch METALS back and forth between different degrees of firmness.  They placed precious metals (gold, platinum, what have you) in an acid bath. The acid corroded the metals, creating teensy tiny holes and channels all through the material, which they subsequently filled with a conductive liquid (dilute acid or saline solution).

Image courtesy Technical University of Hamburg and the Helmholtz Center Geesthacht

Ions dissolved in the conductive liquid influence the surface atoms of the metal, withdrawing or adding electrons to the metal’s surface atoms depending on the charge of the liquid.  Controlled changes in the atomic configuration can double the strength of the metallic materials, or make it weaker and more damage tolerant (Dillow).  The union of metal and water allows the researchers to alter the properties of the material at the touch of a button – an amazing breakthrough!

These “research findings could, for example, make future intelligent materials with the ability of self healing, smoothing out flaws autonomously….  Specific applications are still a matter for the future. However, researchers are already thinking ahead. In principle, the material can create electric signals spontaneously and selectively, so as to strengthen the matter in regions of local stress concentration. Damage, for instance in the form of cracks, could thereby be prevented or even healed. This has brought scientists a great step closer to their objective of ‘intelligent’ high performance materials.” (Source: Eurekalert). Not to mention it would make for a pretty sweet Iron Man suit… I’m just saying.

WU XING:
Filed under Metal and Water.

Cited:

Dillow, Clay. “New Nanometal Changes from Hard to Soft at the Flip of a Switch.” Popsci.com. 06/08/11. Accessed 06/09/11. URL.

“Hard or Soft: at the Touch of a Button.” Public release date: 6-Jun-2011. via Eurekalurt URL.

When I think about a gas mask, for some reason my mind flits to a memory of a series of drawings by British sculptor Henry Moore, which I encountered at the Hirshorn while wandering through the Smithsonian one afternoon during college. The London Underground functioned as a shelter during WWII, and Moore made a series of dark gray moody drawings that convey his experiences sleeping in the tunnels along with thousands of other Londoners at the height of the Blitz.  I’m not really sure if any of the drawings actually depicted people wearing gas masks, but that feeling of darkness and suffocation seems like it might be the common thread.

Image courtesy www.tate.org.uk

You may be asking yourself why on earth a person would be thinking about gas masks on a rainy morning while conducting materials research; let me assure you it’s not because somebody forgot to take out the garbage last night (but seriously, how hard is it to take out the trash!?)

Image courtesy thesurvivalzone.com

Gas masks and respirators, worn by emergency response teams and others who require protection from harmful vapors, contain carbon filters (activated charcoal), which traps the toxins before they can enter the lungs. The problem is that once the carbon filter saturates, it allows harmful chemicals to fly on through the canister without so much as a by-your-leave. Emergency workers currently rely on safety protocols that describe the length of time a gas mask can be worn without changing the mask, but there are too many variables to be completely certain that the charcoal filters are working.

In response to this problem, researchers at the University of California, San Diego working with Tyco Electronics have created a new kind of sensor from carbon nanostructures that could be used to warn emergency workers when the filters in their respirators have become saturated and no longer offer adequate protection. The new microsensors can provide a more accurate reading of how much material has been absorbed by the carbon in the filters (R&D Magazine). 

The researchers “assembled the nanofibers into repeating structures called photonic crystals that reflect specific wavelengths, or colors, of light. The wing scales of the Morpho butterfly, which give the insect its brilliant iridescent coloration, are natural examples of this kind of structure.  The sensors are an iridescent color too, rather than black like ordinary carbon. That color changes when the fibers absorb toxins – a visible indication of their capacity for absorbing additional chemicals” (Brown). You can learn more about the nanoscale structures that make up butterfly wings here.

Image: Timothy Kelly, UCSD Chemistry and Biochemistry

 Image: Brian King, UCSD Chemistry and Biochemistry

The UCSD team fabricated nanotubes that are less than half the width of a human hair.  The photonic sensors can be placed on the tips of optical fibers less than a millimeter across, and can be inserted into respirator cartridges.  According to the researchers, the crystals are sensitive enough to detect chemicals such as toluene at concentrations as low as one part per million (R&D Magazine).

I think these sensors have a wider applicability than just gas masks, however.  Green Building certification systems such as LEED or Green Globes give points for “flushing” a building after construction but prior to handing it over to occupants in order to lower the concentration of volatile organic compounds being emitted by things like paint, adhesives, carpet, plastics, etc. Imagine if you could tell by looking at the color of a sensor whether a building is safe to inhabit from a VOC standpoint?

WU XING:

Filed under fire and wood – because of the carbon and the charcoal.

Cited:

Brown, Susan. “New Material Could Improve Safety for First Responders to Emergencies.” UC San Diego News Center. 04/29/11. Accessed 05/02/11. URL.

R&D Magazine. “New Material Could Improve Safety for First Responders to Chemical Hazards.” 05/02/11. Accessed 05/02/11. URL.

Scientists have been working with carbon nanotubes (essentially, rolled up sheets of graphene) to encourage solar cells to convert more of the sun’s energy to electricity.  Theoretically, nanotubes “gather more electrons that are kicked up from the surface of a PV cell, allowing a greater number of electrons to produce a current” (Boyle).  More electrons means more power, so it’s a decent line of research to pursue.

image courtesy roselawgroup.com

In practice, however, using carbon nanotubes in solar cells has proved more complicated than one might like for two reasons: “first, the making of carbon nanotubes generally produces a mix of two types, some of which act as semiconductors (sometimes allowing an electric current to flow, sometimes not) or metals (which act like wires, allowing current to flow easily). The new research, for the first time, showed that the effects of these two types tend to be different, because the semiconducting nanotubes can enhance the performance of solar cells, but the metallic ones have the opposite effect. Second, nanotubes tend to clump together, which reduces their effectiveness” (Chandler). Understanding the differences between the two types of nanotubes could be useful for designing more efficient nanoscale batteries, piezoelectrics or other power-related materials.

Image credit Matt Klug, Biomolecular Materials Group

Graduate students Xiangnan Dang and Hyunjung Yi, MIT professor Angela Belcher and colleagues turned to biology for a solution to these nanochallenges, employing a genetically engineered version of a virus called M13, prone to attacking and infecting bacteria.  M13 can arrange and order nanotubes on a surface.  The virus has peptides that bind to the nanotubes, allowing them to separate the tubes so they can’t short out the circuits, and it also prevents clumping. “Each virus can grip about five to 10 nanotubes each, using roughly 300 of the protein molecules. The viruses were also genetically engineered to produce a layer of titanium dioxide, which happens to be the key ingredient in Grätzel cells, a.k.a. dye-sensitized solar cells… This close contact between TiO2 nanoparticles helps transport the electrons more efficiently” (Boyle).

Interestingly, the viruses also make the nanotubes water-soluble, which could lower manufacturing costs by facilitating the incorporation of nanotubes into solar cells at room temperature.  The virus-built structures enhanced the solar cells’ power conversion efficiency to 10.6 percent from 8 percent. That’s about a one-third improvement, using a viral system that makes up just 0.1 percent of the cells’ weight (Boyle). A little help from biology goes a long way.

WU XING:

I have filed this under fire, because the main idea relates to energy.

Cited:

Boyle, Rebecca. “MIT Researchers use Viruses to Build More Efficient Solar Panels.” Popsci.com 04/25/11. Accessed 04/26/11. URL.

Chandler, David L. “Solar Power Goes Viral.” MIT News Office. 04/25/11. Accessed 04/26/11. URL.

ARCHITERIALS is a year old now, and like most healthy, well-adjusted one-year-olds it needs to be changed constantly, crawls all over my apartment, and makes strange burbling noises.  No, really – it does.  It’s terrifying.

Over the past year I’ve profiled approximately 65 materials and learned about blogging, bacteria, and biscuits, although I must confess that the biscuts were a side project.  A delicious, buttery side project.  Anyhow, to celebrate the birthday of ARCHITERIALS and the fact that the tagline “Investigating architectural materials since 2010” has finally attained temporal legitimacy, I’ve compiled for this, the 10th day of January,  a list of 10 materials from 2010 that are generally awesome.  I’ve also summarized the awesomeness of each material in a brief paragraph, and I’ve tried to frame each one as part of a larger, sort of big-picture trend in materials science that I’m studying.  Should you click on the links and read the detailed posts about each material for more information? Definitely. 

Finally, thank you so much to those who’ve submitted information, followed, liked, and posted photos over the past year, I appreciate it more than you can imagine!  Keep the materials coming and do tell your friends if your friends seem like people who might be interested in ARCHITERIALS.

Ten Awesome Materials from 2010 and Reasons They are Awesome:

1.  Materials that can be deployed in disasters or used to improve living conditions:  Concrete Cloth

Concrete cloth is a concrete-impregnated fabric that is fire-proof, waterproof, moldable, drapeable, durable and generally fantastic.  Applications include: gabion reinforcement, sandbag defenses, ground surfacing/dust suppression, ditch lining, landing surfaces, formwork, spill containment and landfill lining, waterproofing, building cladding, boat ramps, erosion control, roof repair, water and septic tanks.  Concrete cloth solves problems you don’t even know you have, although nothing can repair your terrible relationship with your mother-in-law.   

2.  Sustainable, non-toxic materials:  Reclaimed Wood and Agricultural Fiber Panels

Kirei Board, Kirei Coco Tiles and Kirei Wheatboard made from the non-food portions (stalks and husks) of sorghum, coconut, and wheat plants.  The agricultural fiber that’s not sold by farmers for use in the manufacture of Kirei board takes up space in landfills or gets burned up and pollutes the air – therefore repurposing it cuts down on that sort of thing.  Sustainable building materials make the planet happy, and a happy planet makes for happy people. 

3.  Biodegradable materials:  Arbofoam

As it turns out, lignin can be transformed into a renewable plastic if it’s combined with resins, flax and other natural fibers. The resulting bio-plastic, called Arboform, can be thermoformed, foamed, or molded via injection machines.  It’s durable and super-precise when it’s cast, and it degrades similar to wood into water, humus, and carbon dioxide. It’s very cool stuff indeed and I’d love it if someone would send me information about a project where it’s been used.  Biodegradable materials cut down on landfill and reduce environmental pollution. 

4.  Thermoplastic/thermoelastic/thermoformed/thermo-etcetera materials:  Chemical Velcro

How could you not get excited about an adhesive 10 times stickier than Velcro and the reusable gecko-inspired glues that many research groups have been trying to perfect that comes apart when heated??!  I have been trying without success to get my hands on some of this to build demountable partition walls for my tiny apartment, and I’m not giving up.  Materials that respond to changes in temperature by changing their behavior or attributes will find widespread application in the future. 

5.  Materials that clean and sanitize themselves:  Liquid Glass

Liquid glass a coating that takes advantages of the unique properties of materials at nanoscale.  It is environmentally harmless and non-toxic, and easy to clean using only water or a simple wipe with a damp cloth. It repels bacteria, water and dirt, and resists heat, UV light and even acids.  According to manufacturers, you can spray liquid glass on everything from wood to seeds to your sneakers.  It could someday replace all the toxic cleaning products you currently use to tidy and disinfect, and it reportedly costs about 8 dollars.  Materials that clean and sanitize themselves cut down on the need for toxic chemicals and pollutants. 

6.  Materials that emit light efficiently:   White LED Lights

White LED lights emit more light than a typical 20-watt fluorescent bulb, as well as more light for a given amount of power. With these improvements, the new LEDs can replace traditional fluorescent bulbs for all general lighting applications, and also be used for automobile headlights and LCD backlighting.  Shedding light on any given subject has never been more efficient.  As we transition to alternative forms of energy we are also looking for materials that emit light without using much energy in the first place.

7.  Nanomaterials:  Gold Nanoparticles

Gold nanoparticles can be used to further increase the efficiency of LED lights.  Researchers have implanted the particles in the leaves of aquatic plants, causing the leaves to emit red light.  Theoretically, the light produced by the leaves could cause their chloroplasts to conduct photosynthesis, meaning that no additional energy source would be needed to power the process.  In fact, the leaves would actually work overtime, absorbing CO₂ at night.  Nanomaterials allow us to intervene in processes like photosynthesis with a previously unheard-of degree of delicacy.

8.  Materials that augment already useful material properties:  Bendywood 

Bendywood is wood that has been pre-compressed so that it can be easily bent by hand.  The tension that forms on the outside of a bend merely returns the plant cells to their former shape, and the wood doesn’t break.  The material is delightfully flexible and pliable.  Bendywood was developed for indoor uses such as furniture, handrails, or curved mouldings, and it shows enormous promise.  Materials like Bendywood amplify the appealing properties of familiar materials so that it’s even easier to use them to our benefit.

9.  Bio-based materials:  Green Fluorescent Protein (GFP)

At the intersection of biology and solar tech, there are jellyfish that produce green fluorescent protein (GFP).  Dripping GFP onto a silicon dioxide substrate between two electrodes causes it to work itself into strands, creating a circuit that absorbs photons and emits electrons in the presence of ultraviolet light.  The electron current (aka electricity) can then be used to power your hairdryer.  I’m completely fascinated by materials that help us to blur the boundaries between biological and man-made machines.

10.  Materials that repair themselves:  Bacilla Filla

Bacilla Filla is a material that patches up the cracks in concrete structures, restoring buildings damaged by seismic events or that have deteriorated over time.  Custom-designed bacteria burrows deep into the cracks in concrete, where they produce a mix of calcium carbonate and a special bacteria glue that hardens to the same strength of the surrounding concrete.  Materials that can detect their own flaws and damage and repair themselves will revolutionize the way we build and think about building materials in the future.

Image courtesy pakrockerx.com

I was reminded of the story of King Midas when I heard about a new materials development by researchers in Taiwan led by Yen Hsun Su and colleagues at Academia Sinica in Taipei and the National Cheng Kung University in Tainan.  The scientists are working to find a way to increase the efficiency of LED lights; to that end they’ve synthesized gold nanoparticles and implanted them into the leaves of the Bacopa caroliniana plant, “a perennial aquatic or semi-aquatic creeping herb commonly used as an aquarium plant” (Edwards) in order to induce bioluminescence. 

Image courtesy www.oregonaquatics.com

Apparently “the green pigment in leaves, chlorophyll, is bioluminescent when exposed to high wavelength (400 nanometers (nm)) ultra violet excitation, but the wavelength is much shorter for the photoluminescence of gold nanoparticles, and they emit light at 400 nm” (Edwards).  The team developed sea-urchin shaped gold nanoparticles, (dubbed nano-sea-urchins or NSUs), and were able to excite the chlorophyll in the Bacopa leaves to emit red light.  Theoretically, the light produced by the leaves would in turn cause their chloroplasts to conduct photosynthesis, meaning that no additional energy source would be needed to power the process.  In fact, the leaves would actually work overtime, absorbing CO₂ at night when they would otherwise be … not doing that (Quick).  It might be possible to develop street trees for cities that bioluminesce to light roadways.

Image courtesy www.inhabitat.com

Nano Sea Urchin image courtesy www.conf.ncku.edu.tw

According to Assistant Professor Shih-Hui Chang, “‘light emitting diode (LED) has replaced traditional light source in many display panels and street lights on the road. A lot of light emitting diode, especially white light emitting diode, uses phosphor powder to stimulate light of different wavelengths. However, phosphor powder is highly toxic and its price is expensive. As a result, Dr. Yen-Hsun Wu had the idea to discover a method which is less toxic to replace phosphor powder which can harm human bodies and cause environmental pollution. This is a major motivation for him to engage in the research at the first place'” (Quick).

Would I like to walk along a street under bioluminescent trees that are offsetting my carbon footprint while lighting my way?  Yes.  Do I think that there might be some unintended consequences relating to the implantation of gold nanoparticles into the leaves of plants, a la the story of king Midas?  Absolutely.  What do you think?

WU XING:

I am filing gold nanoparticles under metal and fire. 

Cited:

Edwards, Lin.  “Gold Nanoparticles that Make Leaves Glow in the Dark.” Physorg.com 11/11/10.  Accessed 11/12/10.  URL.

Quick, Darren. “Gold Nanoparticles turn Trees into Street Lights.” Gizmag.com 11/11/10.  Accessed 11/12/10.  URL.

Video snapshots of microgrippers with bidirectional digits closing and opening because of surface chemical modification. (Credit: Jatinder Randhawa, Gracias Laboratory, JHU.)

Microscale engineers at Johns Hopkins are working to develop inexpensive, mass-fabricated microtools that can be deployed in places that aren’t easy to reach (like inside a cow’s bladder, for instance).  The thing that makes these v. tiny tools extra awesome is the fact that they are activated by exposure to chemicals rather than by electricity, which means troublesome wires are no longer needed.  Also cool is the fact that, “chemical-based actuation of mechanical structures … is widely observed in biological actuators and enables autonomous functioning with high selectivity and specificity” (Gracias).* Microtools that do their job (gripping, cutting, clamping, pick-and-place etc.) in the presence of specific chemicals could find widespread application in the world of materials science.

Concept showing a biosensing-microtool component composed of rigid functional elements and hinges (a) as fabricated and (b) on exposure to L-glutamine. This causes the hinges to bend, thereby leading to a concerted motion. (Credit: Aasiyeh Zarafshar, Gracias Laboratory, Johns Hopkins University: JHU).

The researchers are currently “developing biosensing hinges that bend only when they are exposed to specific biochemicals. They can be interconnected with other structural or functional modules using conventional lithographic processes to construct tools (such as grippers) that close or open when exposed to biochemicals” (Gracias).  Using surface modifications based on oxidation and reduction of copper films, the researchers managed to achieve reversible actuation of the hinges (meaning that they can open and close over and over again). 

The microgripper hinges are created by stacking multiple layers of thin films (some of which are pre-stressed).  One or more of the films undergoes a mechanical transformation upon exposure to a chemical such as L-glutamine or acetic acid.  The hinge “functions like a chemical sensor and it responds by bending” (Gracias).  The researchers didn’t stop there: they added ferromagnetic elements to the microgrippers so that they could be moved around using magnets, and they also used the tetherless tools to excise cells from a bovine bladder in a test tube.  The microgrippers were as small as 700?m when open and 190?m when closed (Gracias).

Video snapshot of a tetherless, biochemically actuated microgripper used to excise cells from a sample. (Credit: Timothy Leong, Gracias Laboratory, JHU.)

But it’s not all rose petals and delicate tears of joy running in lazy, meandering patterns down the faces of scientists.  It’s shockingly difficult to engineer the integration of “heterogeneous materials such as metals, polymers, and gels to structure these miniaturized tools using mass-producible lithographic processes…  Improvements in sensitivity and selectivity are needed to mimic the capabilities of commercial chemical sensors. Reversible biochemical actuation over multiple cycles is challenging under physiologically relevant conditions and at room temperature” (Gracias).  It’s also tough to open and close the microgrippers on demand; it can take hours for certain mechanical actions to take place. 

Despite the challenges, the microtools are pretty exciting.  I am imagining tiny swarms moving across the surface of a building searching for and reparing microscopic tears or cracks…

WU XING:

I’m filing the microtools under metal because they bend, but I could see putting them in other categories too based on the way they move and the fact that they incorporate polymers etc.  I didn’t do that, though.

Cited:

Gracias, David. “Biosensing Microtools” Spie.org 09/15/10.  Accessed 09/28/10.  URL.

*I loved citing David Gracias in this article, because I felt like I was ending those sentences with a parenthetical “thank you.”

Image courtesy blogs.theage.com.au

Sometimes human beings lose body parts through unfortunate accidents, and are fitted with prosthetic limbs.  These limbs look like typical arms and legs (unless they don’t) but they can’t respond in as nuanced a manner as arms and legs with skin on them.Recently, scientists at the University of California at Berkeley have made advances in the creation of artificial skin, a material that goes a long way towards “replacing today’s clumsy robots and artificial arms with smarter, touch-sensitive upgrades…  The “e-skin” … comprises a matrix of nanowires made of germanium and silicon rolled onto a sticky polyimide film” (Ingham).  On top of the wires, the researchers laid nano-scale transistors and a pressure-sensitive flexible rubber material.  The assembly can detect pressures comparable to the force required to type on a computer keyboard or to hold an egg.

Credit: Ali Javey and Kuniharu Takei

At nearby Stanford University, a Chinese-born associate professor who has gained a reputation as one of the top women chemists in the United States named Zhenan Bao is leading a team working on artificial skin.  “Their approach was to use a rubber film that changes thickness due to pressure, and employs capacitors, integrated into the material, to measure the difference” (Ingham).  While the response time is within milliseconds, meaning that pressure can be detected almost instantaneously, the material cannot be stretched.  The ability to stretch is an important characteristic of non-artificial skin, and I’m sure they’re going to work on it.

Credit: Ali Javey and Kuniharu Takei, UC Berkeley

Both teams have achieved significant milestones in the field of artificial intelligence, and it’s especially exciting because they’re working with low-cost processing components.  Future artificial skin might be embedded with sensors that respond to chemicals, biological agents, temperature, humidity, radioactivity or pollutants (Ingham).  Bao and her team envision a prototype in the form of a handheld device, or one that can connect “to other parts of the body that have skin sensation. The device would generate a pulse that would stimulate other parts of the skin, giving the kind of signal ‘my (artificial) hand is touching something’, for instance” (Ingham).  Maybe eventually the skin could also have its own iPhone app.

There is, as always, room for improvement; the current sensors respond to constant pressure, whereas human skin can send different signal frequencies (for example, if something feels painful or sharp like a knife or sword, frequency increases to alert us to the threat).  Not only that, it will be massively challenging to connect any artificial skin to a human nervous system in order to restore sensation (Ingham).

This innovation has architectural implications as well, as I see it.  Imagine a wall or even an entire building coated with artificial skin, allowing it to respond to pressure and temperature changes by deforming or giving off heat or changing color or something.  Hmmm.  I smell a project… maybe I’ll have something to add to the LAB page, which has lain dormant since the dawn of ARCHITERIALS…

Image credit http://www.entertainmentwise.com

If there were a Rolling Stone magazine equivalent for the materials science set, graphene would be on the cover.  Graphene consists of “single-atom–thick sheets of carbon prized for its off-the-charts ability to conduct electrons and for being all but transparent” (Service).  Graphene, like Russell Brand, has some intriguing qualities:  it’s extremely strong and highly conductive, which along with its transparency, make it an attractive alternative for use as a transparent conductor.  Everything from computer displays and flat panel TVs to ATM touch screens and solar cells use transparent conductors these days, and finding a material that is strong, thin, and flaw-free has been a challenge. 

Image credit http://www.lbl.gov

According to Moore’s Law, the density of transistors on an integrated circuit doubles every two years.  Silicon and “other existing transistor materials are thought to be close to the minimum size where they can remain effective. Graphene transistors can potentially run at faster speeds and cope with higher temperatures. Graphene could be the solution to ensuring computing technology to continue to grow in power whilst shrinking in size, extending the life of Moore’s law by many years” (Science Daily).  In other words, graphene might be about to drop Jailhouse Rock. 

Since scientists first isolated graphene in 2004, they’ve struggled to produce the carbon sheets in sizes large enough to be useful.  Last year, a group led by University of Texas, Austin chemist Rodney Ruoff grew graphene squares one centimeter square atop flexible copper foils.  A few days ago, a group of researchers led by Jong-Hyun Ahn and Byung Hee Hong of Sungkyunkwan University in South Korea submitted a report in Nature Nanotechnologydescribing their efforts to scale up the approach taken by the Texas team to make graphene sheets large enough for full-screen displays (Service).

The graphene microchip. (Credit: Photo / Donna Coveney)

Ahn and Hong et al used chemical vapor depositionto grow graphene on large sheets of copper foil. A thin adhesive polymer was layered on top of the graphene, and then the copper backing was dissolved away. “Peeling off the adhesive polymer gave them a single graphene sheet. To make their film stronger, they repeated the initial steps, layering four sheets of graphene atop one another. The researchers then chemically treated their graphene sandwich with nitric acid to improve its electrical conductivity.  The film allowed 90% of light to pass through and had an electrical resistance lower than that of the standard transparent conductor made from indium tin oxide (ITO)” (Service).

Credit: Jong-Hyun Ahn et al., Nature Nanotechnology, Advance Online Publication (2010).

Graphene could be used to make more efficient/cheaper solar cells, better large screen displays for electronics, and so on.  If the larger sheet sizes pan out, we might just be looking at the Elvis of materials.  Time will tell.

WU XING:

I’m filing graphene under EARTH because it’s carbon-based.

Cited:

Science Daily. “Breakthrough in Developing Super-Material Graphene.” 01/19/10. Accessed 06/23/10.  URL.

Service, Robert F. “Graphene Finally Goes Big.” Science Now. 06/20/10. Accessed 06/23/10.  URL.

Images courtesy amnh.org and vipnyc.org 

Pinned up along one side of the wall was a row of brilliantly colored butterflies.  They were so glittery and shiny and their patterns so vivid in color that I wanted to sew a coat out of their wings and wear it for the rest of my life.  But I abandoned the idea, reasoning that the colors would probably fade with time and also because a coat made of insect parts is gross.

Fast forward to today and the butterfly wing coat idea is still gross.  However, I did find out that the colors on butterfly wings don’t fade because … wait for it … they are made of crystal nanostructures called gyroids.  “These are ‘mind-bendingly weird’ three-dimensional curving structures that selectively scatter light,” according to Richard Prum, chair and the William Robertson Coe Professor in the Department of Ornithology, Ecology and Evolutionary Biology at Yale (Source: Physorg.com). Geometrically speaking, a gyroid is “an infinitely connected triply periodic minimal surfacediscovered by Alan Schoen in 1970″ (Wikipedia) and it’s highly awesome.  You can think of it as a network of “three bladed boomerangs” if that helps (Physorg.com). 

Image courtesy Wikipedia

The gyroids on butterfly wings are made of chitin, which is a tough starchy material that forms the exterior of insects and crustaceans.  The chitin that makes up the exoskeletons of crabs and scorpions is typically deposited on the outer membranes of cells, and it doesn’t usually take the form of a gyroid. 

The Yale research team used an X-ray scattering technique at the Argonne National Laboratory in Illinois to determine that, “essentially, the outer membranes of the butterfly wing scale cells grow and fold into the interior of the cells. The membranes then form a double gyroid — or two, mirror-image networks shaped by the outer and inner cell membranes. The latter are easier to grow but are not as good at scattering light. Chitin is then deposited in the outer gyroid to create a single solid crystal. The cell then dies, leaving behind the crystal nanostructures on the butterfly wing” (Physorg.com). 

Okay, so the crystal nanostructures come in pretty colors and they’re durable.  But the most exciting aspect of this line of research has to do with solar cells.  Gyroid shapes can improve the efficiency of solar cells and other optical devices. 

Image Credit: Michael Apel, Wikipedia Commons

Researcher Di Zhang and colleagues are turning to the microscopic solar scales on butterfly wings in their search for materials that may improve the already high efficiency of light-harvesting in dye-sensitized solar cells, also known as Grätzel cells after inventor Michael Grätzel. These solar cells can convert 10% of the light energy that strikes them into electricity (Source: ACS). 

Di Zhang and co. used natural butterfly wings as a mold or template to make copies of the solar collectors, and transferred those light-harvesting structures to Grätzel cells. “Laboratory tests showed that the butterfly wing solar collector absorbed light more efficiently than conventional dye-sensitized cells. The fabrication process is simpler and faster than other methods, and could be used to manufacture other commercially valuable devices, the researchers say” (ACS).  The more efficient our solar cells become, the fewer of them we’ll need to manufacture – meaning less waste, less space, less time, and more betterness.

WU XING:

I’m always distracted by things that are shiny. I’m placing this post in the fire category.

Cited:

“Novel Photoanode Structure Templated from Butterfly Wing Scales”, Chemistry of Materials. Provided by ACS via Physorg.com.  Accessed 06/15/10.  URL.

“Colors of Butterfly Wing Yield Clues to Light-Altering Structures” Provided by Yale University via Physorg.com.  Accessed 06/15/10.  URL.