Professor Richard Kaner was awarded the Materials Research Society (MRS) Medal at the 2015 MRS Fall meeting in Boston.
Prof. Kaner delivered his award talk “Synthesis and Applications of Conducting Polymer Nanofibers” at the meeting on December 1, 2015. He was presented the MRS Medal at the MRS Awards Ceremony the next day.
Prof. Kaner is being honored for his “discovery of efficient methods to synthesize water dispersible conducting polymer nanofibers and their applications in sensors, actuators, molecular memory devices, catalysis, and the novel process of flash welding”.
The MRS Medal is awarded annually by the society for a specific outstanding recent discovery or advancement that has a major impact on the progress of a materials-related field. It is one of the highest recognitions a materials scientist can receive.
(Left to right) Albert Polman, MRS Awards Committee Chair, Ric Kaner and Oliver Kraft, 2015 MRS President.
From the Materials Research Society website:
Kaner’s most important breakthrough came just 10 years ago while he was trying to develop a method to create high-surface-area polyaniline for use in sensors. He and his students developed an interfacial polymerization technique analogous to that used to produce nylon. However, while in the nylon reaction, the polymer remains at the interface between aqueous and organic phases. Kaner demonstrated that when polyaniline forms at the interface between an organic phase containing aniline and an aqueous phase containing oxidant and acid, the doped polyaniline created is hydrophilic and immediately goes into the aqueous phase. This results in nanofibrillar morphology with high surface area and excellent sensing properties. Nanostructured conducting polymers can now be made in a simple, easily reproducible process with inexpensive reagents.
Kaner then showed that by changing the acid used, polyaniline nanofibers could be made in different average diameters ranging from 30 nm to 120 nm. Next, he reported an even simpler synthetic route to conducting polymer nanofibers called rapid mixing. He demonstrated that nanofibers are stable indefinitely in water simply by controlling the pH and salt concentration. With this discovery, Kaner created stable water-based dispersions of pure polyaniline (i.e., polyaniline paints and inks that contain no surfactants).
Kaner started a company, Fibron Technologies, Inc., that demonstrated the efficient synthesis of conducting polymer nanofibers at the 100 L scale. These advances have now been taken over by Water Planet Engineering, which is developing advanced membranes for important separations such as cleaning the oily water left after hydraulic fracturing (“fracking”) to recover oil. Future advances in processable conducting polymers developed by Kaner are anticipated to find applications in many products, including sensors, catalysts, and electronic devices.
Kaner has been recognized as a Distinguished Professor of Chemistry and Distinguished Professor of Materials Science and Engineering at the University of California, Los Angeles (2012). He is a Fellow of Materials Research Society (2011) and has received the American Chemical Society Award in the Chemistry of Materials (2012).
From MRS Meeting Scene (by Arthur L. Robinson):
For his MRS Medal Award presentation, Richard Kaner offered a rapid-fire tour of how to make, modify, and use conducting polymer nanofibers, mainly polyaniline, as well as structures fabricated from aniline tetramers. The story begins when he worked with Alan MacDiarmid and Alan Heeger at the University of Pennsylvania to develop conducting polymers. Since the original material was not stable in air, Kaner’s focus shifted to polyaniline. He and his co-workers found that the conductivity of doped polyaniline slowly increased by 1010 when exposed to any strong acid. By mixing aniline, oxidant, and acid, pure nanofibers of polyaniline could be produced that responded much more quickly. They have also synthesized nanofibers of polyaniline derivatives, polypyrrole and polythiophene. A pilot plant that could make 10s of kilograms of material proved the fabrication process is scalable, and a commercial plant is now online to make membranes for a water-purification facility.
Continuing the chemical sensor theme, Kaner reviewed the use of polyaniline nanofibers in chemiresistor sensors, where the resistance of the film changes due to doping when exposed to the chemical to be detected. The high sensitivity of the nanofiber film relative to conventional films was due to their high surface area, which is inversely proportional to the fiber diameter rather than the film thickness. Nanofiber films also enabled very rapid response times, often less than two seconds. The group demonstrated that such a device was able to detect bases as well as acids (e.g., ammonia vapor at levels 25 lower than the odor threshold of the human nose).
To increase the sensitivity to allow detection of weak acids, including toxic agents, it was necessary to modify the polyaniline nanofibers. For example hydrogen sulfide (H2S) could be detected by adding copper chloride (CuCl2), which is converted to hydrochloric acid that dopes the polyaniline. Similar approaches work for a variety of chemicals to be detected. Polyaniline nanofibers decorated with metal nanoparticles of controllable size and uniform dispersion to form metal-polyaniline nanocomposites also enhance sensor response. Kaner described how nanocomposites can also be made into electrically switchable bistable memory devices with a conductivity different of about 1000 based on gold nanoparticles. Similarly, his group figured out how to make a catalyst based on a palladium-polyaniline composite, and other metals and processes are under investigation.
Polyaniline nanofibers exhibit an exceptional photothermal effect in which they instantaneously melt upon exposure to a camera flash. By controlling where light illuminates a nanofiber film by, for example, a copper TEM grid, Kaner’s group created the grid pattern in the film. To make mechanical actuators based on asymmetric films, the researchers illuminated nanofiber-film-coated substrate sufficiently to melt only the top layer of the film and then removed the substrate. Exposing the film to an acid doped the unmelted portion and drove in water, causing the film to bend. Exposing the bent film to a base straightened it out again.
Kaner devoted the last part of his presentation to aniline tetramers. The basic building block of polyaniline and the smallest unit that can contain dopants, tetramers in nanoribbon form surprisingly have the same electrical conductivity as a conventional polyaniline film. Various morphologies from plates to flowers can be obtained by inducing growth with different acid dopants. Assembling the various forms is a hierachical process, progressing from one to three dimensions with time. Plates, for example, can pack into crystalline arrangements with uniform orientation and controllable crystal density and size. To grow them in any desired pattern, Kaner and his colleagues used patterned graphene films on substrates. The crystals grew on the graphene but not where the graphene was absent.
To learn more about Prof. Kaner’s research visit his group’s website.
