Tag Archives: Yang Wang

Adding melanin to make foams and fabrics stronger

Melanin does not have a reputation as a strengthening agent so why these scientists tested it for that purpose is a mystery. From a Nov. 9, 2016 news item on phys.org,

Melanin is the natural molecule in animals’ skin, hair and the iris of eyes that gives them color and helps protect them from ultraviolet light. Someday soon, the pigment could be found in unexpected places such as sofa cushions or clothing—but not for its hue. Scientists have found that adding a small amount of melanin to polyurethane makes it far stronger than the material by itself. …

A Nov. 9, 2016 American Chemical Society (ACS) press release (also on EurekAlert), which originated the news item, expands on the theme,

From durable foam seating and insulation to glossy coatings and stretchy textiles, polyurethane is used in a huge range of products. Although already fairly versatile, polyurethane still has room for improvement. To make it more durable, scientists have tried adding fillers, including silica, carbon nanotubes and graphene oxide. But these efforts have often led to the enhancement of only one physical property at a time, such as tensile strength — how hard a material can be pulled before it snaps — but not toughness — how much energy it can absorb without breaking. Mingqing Chen, Weifu Dong and colleagues wanted to try a new approach: adding melanin, a biomolecule increasingly used in various other materials.

The researchers found that polyurethane containing just 2 percent melanin, extracted from the ink sacs of cuttlefish, had improved tensile strength and toughness. These properties were enhanced about 10 fold, increasing from 5.6 megapascals and 33 megajoules per cubic meter in plain polyurethane to 51.5 MPa and 413 MJ/m3, respectively. Polyurethane by itself could stretch 770 percent before breaking, whereas the melanin-infused version stretched 1,880 percent before rupturing.

Here’s a link to and a citation for the paper,

Superior Performance of Polyurethane Based on Natural Melanin Nanoparticles by Yang Wang, Ting Li, Xuefei Wang, Piming Ma, Huiyu Bai, Weifu Dong, Yi Xie, and Mingqing Chen. Biomacromolecules, DOI: 10.1021/acs.biomac.6b01298 Publication Date (Web): October 17, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

New electrochromic material for ‘smart’ windows

Given that it’s summer, I seem to be increasingly obsessed with windows that help control the heat from the sun. So, this Aug. 22, 2016 news item on ScienceDaily hit my sweet spot,

Researchers in the Cockrell School of Engineering at The University of Texas at Austin have invented a new flexible smart window material that, when incorporated into windows, sunroofs, or even curved glass surfaces, will have the ability to control both heat and light from the sun. …

Delia Milliron, an associate professor in the McKetta Department of Chemical Engineering, and her team’s advancement is a new low-temperature process for coating the new smart material on plastic, which makes it easier and cheaper to apply than conventional coatings made directly on the glass itself. The team demonstrated a flexible electrochromic device, which means a small electric charge (about 4 volts) can lighten or darken the material and control the transmission of heat-producing, near-infrared radiation. Such smart windows are aimed at saving on cooling and heating bills for homes and businesses.

An Aug. 22, 2016 University of Texas at Austin news release (also on EurekAlert), which originated the news item, describes the international team behind this research and offers more details about the research itself,

The research team is an international collaboration, including scientists at the European Synchrotron Radiation Facility and CNRS in France, and Ikerbasque in Spain. Researchers at UT Austin’s College of Natural Sciences provided key theoretical work.

Milliron and her team’s low-temperature process generates a material with a unique nanostructure, which doubles the efficiency of the coloration process compared with a coating produced by a conventional high-temperature process. It can switch between clear and tinted more quickly, using less power.

The new electrochromic material, like its high-temperature processed counterpart, has an amorphous structure, meaning the atoms lack any long-range organization as would be found in a crystal. However, the new process yields a unique local arrangement of the atoms in a linear, chain-like structure. Whereas conventional amorphous materials produced at high temperature have a denser three-dimensionally bonded structure, the researchers’ new linearly structured material, made of chemically condensed niobium oxide, allows ions to flow in and out more freely. As a result, it is twice as energy efficient as the conventionally processed smart window material.

At the heart of the team’s study is their rare insight into the atomic-scale structure of the amorphous materials, whose disordered structures are difficult to characterize. Because there are few techniques for characterizing the atomic-scale structure sufficiently enough to understand properties, it has been difficult to engineer amorphous materials to enhance their performance.

“There’s relatively little insight into amorphous materials and how their properties are impacted by local structure,” Milliron said. “But, we were able to characterize with enough specificity what the local arrangement of the atoms is, so that it sheds light on the differences in properties in a rational way.”

Graeme Henkelman, a co-author on the paper and chemistry professor in UT Austin’s College of Natural Sciences, explains that determining the atomic structure for amorphous materials is far more difficult than for crystalline materials, which have an ordered structure. In this case, the researchers were able to use a combination of techniques and measurements to determine an atomic structure that is consistent in both experiment and theory.

“Such collaborative efforts that combine complementary techniques are, in my view, the key to the rational design of new materials,” Henkelman said.

Milliron believes the knowledge gained here could inspire deliberate engineering of amorphous materials for other applications such as supercapacitors that store and release electrical energy rapidly and efficiently.

The Milliron lab’s next challenge is to develop a flexible material using their low-temperature process that meets or exceeds the best performance of electrochromic materials made by conventional high-temperature processing.

“We want to see if we can marry the best performance with this new low-temperature processing strategy,” she said.

Here’s a link to and a citation for the paper,

Linear topology in amorphous metal oxide electrochromic networks obtained via low-temperature solution processing by Anna Llordés, Yang Wang, Alejandro Fernandez-Martinez, Penghao Xiao, Tom Lee, Agnieszka Poulain, Omid Zandi, Camila A. Saez Cabezas, Graeme Henkelman, & Delia J. Milliron. Nature Materials (2016)  doi:10.1038/nmat4734 Published online 22 August 2016

This paper is behind a paywall.

Smart windows from Texas (US)

I’ve been waiting for ‘smart’ windows and/or self-cleaning windows since 2008. While this research on ‘smart’ windows at the University of Texas at Austin looks promising I suspect it will be years before these things are in the marketplace. A July 22, 2015 news item on Nanotechnology Now announces the latest research,

Researchers in the Cockrell School of Engineering at The University of Texas at Austin are one step closer to delivering smart windows with a new level of energy efficiency, engineering materials that allow windows to reveal light without transferring heat and, conversely, to block light while allowing heat transmission, as described in two new research papers.

By allowing indoor occupants to more precisely control the energy and sunlight passing through a window, the new materials could significantly reduce costs for heating and cooling buildings.

In 2013, chemical engineering professor Delia Milliron and her team became the first to develop dual-band electrochromic materials that blend two materials with distinct optical properties for selective control of visible and heat-producing near-infrared light (NIR). In a 2013 issue of Nature, Milliron’s research group demonstrated how, using a small jolt of electricity, a nanocrystal material could be switched back and forth, enabling independent control of light and energy.

A July 23, 2015 University of Texas at Austin news release, which originated the news item, provides more details about the research which has spawned two recently published papers,

The team now has engineered two new advancements in electrochromic materials — a highly selective cool mode and a warm mode — not thought possible several years ago.

The cool mode material is a major step toward a commercialized product because it enables control of 90 percent of NIR and 80 percent of the visible light from the sun and takes only minutes to switch between modes. The previously reported material could require hours.

To achieve this high performance, Milliron and a team, including Cockrell School postdoctoral researcher Jongwook Kim and collaborator Brett Helms of the Lawrence Berkeley National Lab, developed a new nanostructured architecture for electrochromic materials that allows for a cool mode to block near-infrared light while allowing the visible light to shine through. This could help reduce energy costs for cooling buildings and homes during the summer. The researchers reported the new architecture in Nano Letters on July 20.

“We believe our new architected nanocomposite could be seen as a model material, establishing the ideal design for a dual-band electrochromic material,” Milliron said. “This material could be ideal for application as a smart electrochromic window for buildings.”

In the paper, the team demonstrates how the new material can strongly and selectively modulate visible light and NIR by applying a small voltage.

To optimize the performance of electrochromics for practical use, the team organized the two components of the composite material to create a porous interpenetrating network. The framework architecture provides channels for transport of electronic and ionic change. This organization enables substantially faster switching between modes.
Smart Window

The researchers are now working to produce a similarly structured nanocomposite material by simple methods, suitable for low-cost manufacturing.

In a second research paper, Milliron and her team, including Cockrell School graduate student Clayton Dahlman, have reported a proof-of-concept demonstrating how they can achieve optical control properties in windows from a well-crafted, single-component film. The concept includes a simple coating that creates a new warm mode, in which visible light can be blocked, while near-infrared light can enter. This new setting could be most useful on a sunny winter day, when an occupant would want infrared radiation to pass into a building for warmth, but the glare from sunlight to be reduced.

In this paper, published in the Journal of the American Chemical Society, Milliron proved that a coating containing a single component ­— doped titania nanocrystals — could demonstrate dynamic control over the transmittance of solar radiation. Because of two distinct charging mechanisms found at different applied voltages, this material can selectively block visible or infrared radiation.

“These two advancements show that sophisticated dynamic control of sunlight is possible,” Milliron said. “We believe our deliberately crafted nanocrystal-based materials could meet the performance and cost targets needed to progress toward commercialization of smart windows.”

Interestingly, the news release includes this statement,

The University of Texas at Austin is committed to transparency and disclosure of all potential conflicts of interest. The lead UT investigator involved with this project, Delia Milliron, is the chief scientific officer and owns an equity position in Heliotrope Technologies, an early-stage company developing new materials and manufacturing processes for electrochromic devices with an emphasis on energy-saving smart windows. Milliron is associated with patents at Lawrence Berkeley National Laboratory licensed to Heliotrope Technologies. Collaborator Brett Helms serves on the scientific advisory board of Heliotrope and owns equity in the company.

Here are links to and citations for the two papers,

Nanocomposite Architecture for Rapid, Spectrally-Selective Electrochromic Modulation of Solar Transmittance by Jongwook Kim, Gary K. Ong, Yang Wang, Gabriel LeBlanc, Teresa E. Williams, Tracy M. Mattox, Brett A. Helms, and Delia J. Milliron. Nano Lett., Article ASAP DOI: 10.1021/acs.nanolett.5b02197 Publication Date (Web): July 20, 2015

Copyright © 2015 American Chemical Society

Spectroelectrochemical Signatures of Capacitive Charging and Ion Insertion in Doped Anatase Titania Nanocrystals by Clayton J. Dahlman, Yizheng Tan, Matthew A. Marcus, and Delia J. Milliron. J. Am. Chem. Soc., 2015, 137 (28), pp 9160–9166 DOI: 10.1021/jacs.5b04933 Publication Date (Web): July 8, 2015

Copyright © 2015 American Chemical Society

These papers are behind paywalls.