Surface smarts

(Nanowerk News) Chih-hung Chang's work is mostly invisible. Chang, an Oregon State University professor of chemical engineering and materials science, develops thin films and nanomaterials that are, in many cases, only one molecule thick.
Yet these materials have potential applications just about everywhere, from ski slopes to solar farms. Someday, you might even find yourself wearing one of Chang’s creations — on a T-shirt embedded with smart textile technology.
“I love coming up with new ideas,” Chang said. “It’s always exciting to try something different.”
Chih-hung Chang and graduate student Zhongwei Gao discuss the specs for a new type of nanomaterial printer
Chih-hung Chang and graduate student Zhongwei Gao discuss the specs for a new type of nanomaterial printer. (Image: Oregon State University)
One of Chang’s biggest and most successful ideas to date has been a way to control chemical reactions with microreactors, a process he helped invent in 2002. Today, supported largely by the National Science Foundation, Chang cooks up a wide array of nanomaterials, nanostructures, and thin films in these microreactors. Those materials and films can in turn be used to create devices such as sensors, transistors, and solar cell materials.
“The reactor itself does not have to be microscale,” Chang explained. “But it uses microscale features inside to optimize heat and mass transfer. Reactants go into the reactor and form different chemical species. These reaction products change over time. So, with a high level of precision, you can control the output. We use the microreactor to create nano building blocks, which we can then deposit onto a surface to make nanostructured materials and films.”
Chang’s group combines patterns of these nano-sized building blocks to build functional surfaces directly on a substrate. Tweaking these surfaces can, for example, change the optical properties of glass to make solar cells more efficient.
In 2007, Chang founded a spinoff company to advance the application of this research. Pellucere Technologies, Inc. (formerly CSD Nano, Inc.) developed a process to retrofit solar cells in the field with an antireflective and anti-soiling silica coating called MoreSun, which increases energy output up to 4.7%. The company is set to begin full-scale commercial deployment after securing major investment from Energy Innovation Capital. Chang currently sits on Pellucere’s board.
Chang is also using his microreactors to develop molecular and nanoparticle inks that can be used to print electronics using additive techniques. The process works exactly like conventional inkjet printing: A silicon microfluidic chip dispenses tiny droplets of different inks with a very high degree of precision and accuracy. Only with this printer, instead of producing different colors, the inks function as conductors, semiconductors, and insulators.
Chang has racked up some significant breakthroughs in printable electronic components. His group was the first to print a metal oxide transistor in 2004, followed by a p-type copper iodide transistor that same year, and a copper indium selenide solar cell in 2012. A more recent project, supported by the Walmart Manufacturing Innovation Foundation, aims to print electronic devices directly onto fabrics.
Someday, Chang says, smart textiles could be used to create T-shirts that keep smartphones charged using solar energy. Or perhaps the shirt will contain embedded sensors to collect information about wearers’ health or alert them to hazards in the environment.
“Right now, we’re at the stage where we want to be able to fabricate components onto the textiles, including transistors or solar cells,” he said.
Some of Chang’s research has already made an impact in the field of wearable technology. Portland-based Abom, Inc. turned to Chang to help further develop its patented self-defogging ski goggles that rely on an efficient transparent heater. Supported by the Oregon Nanoscience and Microtechnologies Institute, Chang worked with Rajiv Malhotra, assistant professor of mechanical and aerospace engineering at Rutgers University, to develop innovative processes of making curved transparent heaters based on silver nanowires.
And just last year, Chang worked with researchers at Rutgers to create silver nanowire patches that can be woven into garments to provide localized heating. In addition to potential medical applications, this innovation could result in substantial energy savings. For example, businesses could use heated garments to keep warehouse workers warm in winter, rather than heating the entire warehouse.
One promising new area of Chang’s work involves developing functional inks that can be used in combination with 3D printing technology to modify the properties of printed materials. In collaboration with Oregon State colleagues Brian Paul, professor of manufacturing engineering, and Somayeh Pasebani, assistant professor of advanced manufacturing, Chang’s group wants to use this process to incorporate oxide nanoparticles into stainless steel to create oxide dispersion strengthened alloys.
These materials are used in high-temperature applications such as heat shields for spacecraft, and in heat exchangers for high-tech cooling applications. Chang is also working to develop printing processes for perovskite materials, used in a variety of applications including photovoltaics, lasers, and LEDs.
Another developing area of interest has to do with using microreactors to control the creation of metal-organic frameworks, or MOFs. These labmade chemical structures combine metal ions or clusters with organic links to form molecular cages that can be designed to selectively adsorb specific types of gas.
Chang is working with Oregon State colleagues Cory Simon, assistant professor of chemical engineering, and Alan Wang, associate professor of electrical and computer engineering, on a project that will combine MOFs with fiber optic technology to create optical sensors to measure the levels of specific gases, such as carbon dioxide, in gas mixtures.
One principle underlying all of Chang’s projects is developing sustainable and scalable manufacturing processes for nanomaterials by reducing energy consumption and achieving higher material utilization.
“The hope is that by making these processes more efficient, devices will be more cost-effective so they can be commercialized and brought to market,” Chang said.
Source: Oregon State University
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