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Volume 90 Issue 13 | pp. 28-33
Issue Date: March 26, 2012

Serious Surfaces

Material innovations on the exterior of consumer products bring new functionalities
Department: Business
Keywords: surface chemistry, nanotechnology, consumer electronics, LEDs, paints and coatings, plasma deposition, consumer products
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FLEX TEST
Researchers at Corning measure the strength of Gorilla Glass.
Credit: Corning
Bending Gorilla Glass at Corning as part of a stress test.
 
FLEX TEST
Researchers at Corning measure the strength of Gorilla Glass.
Credit: Corning

In a word association game, most consumers would not respond to the word “glass” with the word “rugged.” Yet many people are carrying rugged glass in their pockets. Today’s leading mobile devices are topped by a layer of chemically strengthened glass that protects their screens from the damaging forces of the outside world, not to mention keys, coins, and all the other stuff people carry around.

Use of the glass, called Gorilla Glass and made by Corning, is one example of how material advances at the surface are making consumer products more functional. Many of these innovations were developed for the electronics industry, but they are also at work in cosmetics, clothing, paint, and lighting. As more consumer products are made wear-resistant, touch-sensitive, water-repellent, and even just more pleasing to the eye, shoppers can thank surface chemistry.

For manufacturers of advanced materials, the road to getting their products into consumer goods can be long, says Mark McClusky, president of Newry, a product commercialization strategy firm that works with advanced-materials companies. Corning’s strengthened glass was first developed in the 1950s but not commercialized until 2007. That timeline sounds extreme, but it is not atypical, according to McClusky.

In the future, the rapid pace of innovation in interactive gadgets will open additional avenues for surface chemistry, McClusky says, particularly in consumer electronics because of the way that people interact with them. “Coevolution of products and processes allows that to happen over time,” he says. “Once a surface material can be added as part of a routine industrial process, we can see combinations that never could have happened before because it could not be done at a reasonable cost.”

Back in the late 1950s, of course, innovations in glass chemistry had nothing to do with smartphones. Instead, says Donnell Walton, manager of worldwide applications engineering at Corning, researchers were looking for a way to unite the transparency of glass with the toughness of metal. One target market for what was then called Project Muscle was windshields for cars, helicopters, and airplanes.

“Why is it that glass is not considered tough?” asks Walton, who is a physicist. “It is an amazingly strong material—theoretically one of the strongest ones known, but only under compression.” Imagine trying to crush a sheet of glass under a stack of heavy books. Under tension, however, glass is brittle. The typical failure mode is bending to break. Scientists figured they could build some compression into the glass to overcome the forces that cause it to fail.

Corning turned to ion-exchange chemistry. Sheets of glass are placed in a bath of 400 °C molten salts. Sodium ions leave the surface of the glass and enter the salt bath, and potassium ions take their place. When the glass cools, the larger potassium ions are pushed together, forming a layer of compressive stress on the surface. The method was pretty much perfected 50 years ago but was not commercialized. The windshield idea didn’t pan out; instead windshields are made of laminated safety glass—two pieces of curved glass sandwiching a layer of clear plastic film.

As some Apple fans know, Corning’s special glass process was revived for use in the first iPhone, introduced in 2007. Corning is still not permitted to disclose that it is a supplier to Apple. However, Walter Isaacson’s authorized biography of Steve Jobs describes a meeting between the former Apple chief executive officer and Wendell P. Weeks, CEO of Corning, in which Jobs told Weeks that he wanted to use Gorilla Glass instead of plastic on his new phone to prevent scratches.

To ensure that Gorilla Glass would ward off damage inflicted by sometimes-clumsy cell phone users, Corning obtained a large number of broken phones. “Many of them came to us looking like jigsaw puzzles,” Walton recalls. Researchers used fractography to trace the break patterns. Once they understood the primary modes of failure, such as sharp impact damage, they designed lab tests to replicate the damage. One test mimicked the environment of a person’s pocket or handbag by putting the device in a large bucket with keys, lipstick tubes, and the like, then spinning it to see if scratches would result.

The hardened surface also had to be quite thin. Earlier touch screens would bend when touched, sending information to the processor. Today’s touch screens use parallel-plate capacitive technology, where one plate is the phone and the other is the finger. Underneath the glass, a layer of capacitive materials holds an electric charge. Touching the phone completes a circuit and changes the amount of charge at the point of contact. Phone makers needed to minimize the space between the finger and the sensors underneath the glass. Walton says Gorilla Glass can be made thin in part because it doesn’t require a protective coating. “Being a glass company, we’re going to try to solve the problem with glass. It turned out to be a pretty good solution,” he says.

A different coating material gives smartphone screens their sleek border of opaque black. In addition to being aesthetically pleasing, the black area hides the underlying electronics and blocks errant light emitted from the screen. To get a rich and opaque black, manufacturers use a thin coating of carbon black, made by companies such as Cabot Corp. But the push for thinner touch screens presents a dilemma for carbon black makers, says Josh Preneta, Cabot’s global segment manager for coatings.

Standard touch-screen configurations use carbon black printed onto glass, often Gorilla Glass, plus two additional layers of film. The layers are insulated polyester films, each containing a set of nanowires of indium tin oxide (ITO). One layer has wires in the x direction and one in the y direction. However, new, thinner devices call for printing the ITO directly on the cover glass, putting it in contact with the black mask.

“If the ITO runs over a surface that is conductive, you get interference, and the touch screen no longer works,” Preneta explains. And regular carbon black powder is somewhat conductive. To work around the problem, Cabot needed to develop a resistive carbon black. The coating also needed to be made much thinner to ensure that the touch signal would reach the ITO layer. A standard screen uses a 10-μm layer of carbon black, whereas new touch screens call for a layer only 1–2 μm thick. “To retain the opaqueness we need a higher concentration of carbon black, compounding the possible conductive problems,” Preneta says.

Carbon black particles have a morphology that is similar to a cluster of grapes, Preneta says, and modifying that structure contributed to the solution. “We can manipulate the number of grapes in each cluster and the size of the grapes, which enables us to make it more conductive or less conductive.” In addition, Cabot developed a chemical treatment that eliminates the ability of electrons to jump from one carbon black particle to another. The thinner touch-screen products that recently hit the market feature the modified carbon black.

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Hydrophilic pigment particles for cosmetics
Credit: Gelest
Hydrophilic pigment particles for cosmetics
 
Hydrophilic pigment particles for cosmetics
Credit: Gelest

Although they seem a world away from smartphone technology, cosmetics also can get a performance boost from modified particles. Specialty materials firm Gelest manufactures synthetic particles and adds functionality to natural or synthetic particles, says Joel Zazyczny, Gelest’s vice president for silanes, silicones, and metal organics. Although the firm’s core markets are generally high-tech materials, semiconductors, pharmaceuticals, separation technologies, composites, and optoelectronics, Gelest is now helping major cosmetic brands differentiate their products through new functionality.

Beginning with common particles used in the color cosmetics industry—iron oxide pigments, mica, talc, and titanium dioxide—Gelest adds tailored surface chemistry to make personal care products pH-stable, water-attracting or water-repelling, oil-repelling, easily dispersible, smooth-flowing, and smooth-feeling. To do this, the company turns to specialty silanes and silicones to put reactive surfaces on the micrometer-sized particles.

The methods borrow from industrial coating technologies that make products last longer by adding anticorrosion or water-repellent characteristics. “The particles used in cosmetics already have surface chemistries—pH, oil absorption, surface area, charge, and particle-size distribution. Once we understand the multiple facets of the particles, we can design the surface treatment to optimize the desired effect,” Zazyczny says. The added silane or silicone materials are used as surface modifiers or as coupling agents. When assembled on the particle surface, they bring with them functional groups that are either useful in themselves or allow Gelest to attach other molecules.

Gelest’s first target products include mascaras, eyeliners, and pressed powders for high-end makeup brands. Similarly, functional particles can be used in skin care products for wrinkle control. They can modify particles to fill in the wrinkled areas by matching particle shape, size, and surface properties to the curvature of the skin. Particles can also offer light-scattering effects to give the appearance that the wearer doesn’t have wrinkles, Zazyczny reports.

At coatings firm PPG Industries, functional particles are part of a recipe for dirt-resistant exterior house paint. In contrast to Gelest, however, PPG had to find low-cost materials that would work for the large-scale consumer paint market.

According to Beth Kirol, technical manager for exterior latex coatings, most house paint has a flat or matte finish that helps to hide imperfections in underlying wood, stucco, or other building materials. To achieve the flat effect, latex paints contain silicates, talc, clays, and diatomaceous earths that decrease the sheen. But those ingredients make the surface of the paint porous, allowing it to pick up and hold on to dirt.

The trick was to find an additive that would fill in the nooks and crannies in the surface without changing the flat finish or wearing off from weathering. “Different paint manufacturers have their own approach,” Kirol says. The additive can be inorganic or organic in nature, but by and large they are inorganic, she explains. A review of technical information from paint ingredient makers DuPont, BASF, and Dow Chemical shows that options include fluorosurfactants, nanosized silica particles modified with siloxane, and polymeric nanoparticles functionalized with silicon or fluorine.

For its Olympic Premium house paint, available at Lowe’s stores, PPG uses inorganic nanoparticles to control the morphology at the surface of the paint. Kirol says the addition makes the paint somewhat hydrophilic, meaning dirt will come off more easily when rinsed with rain. The precise nature of the particle is a trade secret, but product literature mentions a likely candidate: SiO2 particles less than 10 µm in size.

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DRY FEET
Water-resistant nanocoatings from P2i can be added to shoes using plasma deposition technology.
Credit: P2i
P2i uses plasma deposition to place a nanolayer of particles on products for water resistant coatings.
 
DRY FEET
Water-resistant nanocoatings from P2i can be added to shoes using plasma deposition technology.
Credit: P2i

A very different nanotechnology—borrowed from the semiconductor industry—is helping make shoes water-resistant. U.K.-based start-up P2i has commercialized a plasma deposition process that adds a nanometer-thick layer of polymer to the surface of shoes, textiles, and hearing aids. According to Nick Rimmer, the company’s applications director, the process significantly reduces the surface energy of a product, meaning that when liquids splash on, they form beads and run off.

The technology was developed in the 1990s by the U.K.’s Ministry of Defence for uniforms that could repel chemical and biological weapons. But the ministry recognized the technique’s commercial potential and spun off the company in 2004. Since then, P2i has ramped up its technology; more than 3 million pairs of shoes have been treated so far, according to Rimmer. The firm lists Timberland, K-Swiss, and Teva among its customers.

The P2i process starts with a perfluorinated carbon monomer that is applied inside a vacuum chamber. In the low-pressure environment, a plasma activates the surface of the product—the shoe, say—being treated, allowing the monomer to form a covalent bond with the surface. The plasma also polymerizes the monomer to form a film. The process coats the entire shoe, including the laces, and covers problem areas such as the holes left where fabric or leather is sewn together. P2i says the thin coating does not alter the breathability of the material.

Rimmer reports that the technology works well on a variety of shoes. “The challenges we faced were all about industrialization and scaling up to deal with the volumes our brands need us to accommodate,” he says. Adapting the process to work with fully automated industrial equipment means P2i’s facility in China can process tens of thousands of shoes a day.

P2i made its first product breakthrough by coating hearing aids. As Rimmer points out, a hearing aid is a vulnerable and expensive piece of electronics that is worn inside the body and also exposed to the elements. The firm found it a strong market niche because most manufacturers cover their products against damage with a warranty and P2i’s customers were suffering from high return rates. P2i’s process decreased returns by about 50%, according to Rimmer, and within two years, half of all new hearing aids had the coating.

The hearing aid success meant P2i could quickly ramp up its business, which helped it to then tackle the footwear industry.

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TOUGH STUFF
The Motorola Droid Razr smartphone sports Corning’s Gorilla Glass and a water-resistant nanocoating from P2i.
Credit: Motorola
Motorola Droid RazR has Corning’s Gorilla Glass and water-resistant nano-polymer coating by P2i.
 
TOUGH STUFF
The Motorola Droid Razr smartphone sports Corning’s Gorilla Glass and a water-resistant nanocoating from P2i.
Credit: Motorola

In a neat applications twist, new uses of the technology include adding a layer of water repellency to smartphones such as Motorola’s Razr. In addition to P2i’s splash-guard coating, the Razr has a case made of DuPont’s Kevlar and a Gorilla Glass screen.

Though electronics, shoes, and textiles are huge markets for water-resistant coatings, Rimmer reports that the business is looking to expand to other industries. Its water- and oil-repellent coating could be used to coat air filters to extend the product life, especially in tough applications such as automobiles. Looking further to the future, Rimmer says, “With a change of chemistry, we could introduce a change in functionality at the surface.” Other types of invisible coatings that could be applied in a nanolayer with plasma deposition include antimicrobial, antiscratch, and anti­fingerprint surfaces.

Improvements in functional coatings may soon make light-emitting-diode lamps as popular with consumers as smartphones. Although LEDs are extremely energy-efficient, the poor quality of the light and high up-front costs have prevented widespread adoption for home use. But later this year, consumers will be able to purchase LED lights that will mimic the warm tones and light quality of old-fashioned incandescent bulbs. One new light, the Switch Bulb, made by the San Jose, Calif.-based firm of the same name, will be available to consumers starting midyear in a version that emits an amount of light similar to a 60-W incandescent bulb.

Until recently, most LED lights consisted of a blue-wavelength LED chip topped with a yellow phosphor coating. The combination emits light in a blue peak and a yellow peak, which together appear as white to the human eye. But consumers have noted that the white light is cooler than the yellowish tone of an incandescent bulb, and the color of many objects is difficult to make out under LEDs.

The phosphor coating is made by combining a base material, usually a common metal, and a rare earth such as cerium or europium that forms activators to absorb light in the blue spectrum and emit it at longer wavelengths. For example, yellow phosphors are made of yttrium aluminum garnet doped with cerium.

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Intematix tests different color LED phosphors
Credit: Intematix
Intematix tests different color LED phosphors
 
Intematix tests different color LED phosphors
Credit: Intematix

At phosphor maker Intematix, based in Fremont, Calif., researchers have developed new phosphors that help LEDs emit light in the full color spectrum. “Red is a commercial star” for bringing warm light, says Julian Carey, senior director of marketing at Intematix. Early attempts with red phosphors caused the energy efficiency of LEDs to drop because too much of the emitted light fell outside the visible range. High-throughput screening of materials has helped Intematix develop red nitride phosphors that are more efficient.

Finding the perfect set of phosphors has been the major hurdle for getting LED lighting into the consumer market, Newry’s McClusky observes. “As those problems are resolved, you will see a widespread use of LED lighting,” he predicts.

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PIGMENT POWER
Colored particles for cosmetics can be made hydrophobic with surface modification.
Credit: Intematix
Intematix develops phosphor coatings for LED lights.
 
PIGMENT POWER
Colored particles for cosmetics can be made hydrophobic with surface modification.
Credit: Intematix

Using phosphors as coatings for LEDs has other drawbacks, Carey says. When the phosphors are bound directly to the LED chip, some of the blue light that is absorbed is then reflected back toward the chip, rather than out. This heats up both the phosphor and the chip, and creates one intense point of light. Companies that make LED lamps—what consumers put in their light fixtures—have to build in heat sinks made of heavy aluminum fins and add optical diffusers to spread out the light. Excess heat can shorten the LED’s life span, and the additional metal parts add to the production costs.

To help improve the design of LED lamps, Intematix is developing what the industry calls remote phosphors. The blue LED light would go into a highly reflective chamber and exit through a window made of specially manufactured phosphors. From there, the longer wavelength light would be reflected out in a diffuse pattern. Carey says that Intematix testing has shown that the new phosphors would redirect 30% of the energy that would otherwise be lost as heat.

Intematix is not a phosphor supplier for Switch Bulbs. However, Dave Horn, the chief technology officer at Switch, is keen to check out the new remote phosphors. Switch has focused on cooling technologies for its LED lamp design. Rather than add a complicated aluminum ruffle that acts as a heat sink, the Switch bulb uses liquid cooling technology inside a smooth metal base. The LEDs still get hot, but not as hot as in standard models, thanks to heat convection through the liquid. Switch was able to avoid problems with degradation of the liquid in the hot lamp by choosing a stable cosmetic-grade fluid.

The fluid lowers the lamp’s operating temperature by 20 °C. “Because it’s cooler, it has a longer lifetime. But most consumers don’t need a lightbulb that lasts 57 years,” Horn says. “Alternatively, we could put more electricity in, and get more light out. But we chose to use the less efficient LED phosphors which allow us to get the highest quality of light” using the same amount of electricity as the competitors’. Using remote phosphors would increase the ability to produce pleasing light, Horn says. “If I now have a gap between the LED chip and the phosphors, I have better convection. I can allow my fluid to cool the chip directly.”

LED phosphors join Gorilla Glass among examples of how functional surface materials are key to consumer product innovations. Although many were developed for high-priced electronics, the materials and the processes for applying them have evolved and are now ready to be used on a large scale, Newry’s McClusky says. “Surface materials that can impart a property or attribute to a product that it didn’t have before—making it easy to clean, water-resistant, scratch-resistant, or otherwise better—are opening up into whole new categories of uses.”

 
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