BM10: Bioinspired Interfacial Materials with Superwettability

Dimos Poulikakos, ETH Zürich

Enhancing Superhydrophobicity and Icephobicity through Surface Flexibility Inspired by Butterfly Wings

Written by Aashutosh Mistry

Butterfly wings have incited a bit of scientific interest for fluid dynamists as they are very hydrophobic. Surface investigations have revealed that the surface itself is superhydrophobic with contact angles in the range 155°–165° (with 5° hysteresis). Since butterfly wings are flexible structures, an associated question is the role of flexibility on hydrophobicity (i.e., if it promotes or discourages the intrinsic hydrophobicity of the wings). Dimos Poulikakos and his research group at ETH Zürich have been investigating the importance of surface flexibility on hydrophobicity as well as icephobicity. They found that when water drops impact the solid substrate at a finite velocity, resulting rebound is higher for a more flexible surface, thus highlighting a positive correlation between flexibility and hydrophobicity. Even the harmonics of drop oscillations are found to differ based on the extent of surface flexibility. Based on their experiments, they found that the mass weighted relative velocity of drop and the surface is an important velocity scale. Use of this relative velocity collapses the results with both rigid and flexible surfaces onto a unique scaling relation. When extending such studies for supercooled surfaces (surface at temperatures below freezing point of water), they made some interesting observations. The entire water drop does not solidify instantaneously. Rather in many instances they found that the drop rebounds (again depending on surface flexibility) and freezes mid-air. A spontaneous formation of minute icicle network is observed inside the drop upon contact. Icephobicity is practically quite relevant because ice formation on operating surface can largely hinder their performance. The present set of results show that if the surface is assigned a control motion, solidifying drops will not adhere to the surface. Thus, it is observed that the surface elasticity and wetting properties have a collaborative effect that is tunable through altering substrate areal density, stiffness, and damping.


Best Poster Award Winners - Thursday

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Shan Yan, State University of New York
BM06.12.13
Flexible Electronic Devices with Functional Nanoparticles Towards Wearable Biosensors for Human Health and Performance Monitoring

 

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Seirjiro Fukuta, Yamagata University
EM01.10.10
Poly(3-Hexylthiophene)-b-Poly(isobutene)-b-Poly(3-hexylthiophene) for Stretchable Semiconductor Application

 

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Kostianty Turcheniuk, Georgia Institute of Technology
ES04.19.49
Nanoporous Copper Synthesized via De-Alloying of Copper-Calcium Alloys to Accommodate Lithium Titanate for Asymmetric Supercapacitors



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Kriti Agarwal, University of Minnesota
NM02.11.43
Uniform Plasmon Hybridization and Volumetric Field Enhancements in Graphene Nanocubes

 

NOT PICTURED

Rohit Saraf, University of Waterloo
ES01.13.53
Photo Assisted Poling Effect in Organic-Inorganic Hybrid Perovskite and Its Application for Self-Powered Tactile Sensors


Graduate Student Awards

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Gold  Winners:

Longji Cui, University of Michigan

Yuzhang Li, Stanford University

Naveen Mahenderkar, Missouri University of Science and Technology

Patrick Pietsch, ETH Zürich

Michelle Sherrott, California Institute of Technology

Birgitt Stogin, The Pennsylvania State University  *Nowick

John Sypek, University of Connecticut

Sirimuvva Tadepalli, Washington University in St. Louis

Ryan Truby, Harvard University


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Silver Winners:

Arif Abdullah, University of Illinois at Urbana-Champaign

Dennis Christensen, Technical University of Denmark

Maher Damak, Massachusetts Institute of Technology

David Frazer, University of California, Berkeley

Yongping Fu, University of Wisconsin–Madison

Alex Ganose, University College London

Grace Gu, Massachusetts Institute of Technology

Yuanwen Jiang, The University of Chicago

Kang Hee Ku, Korea Advanced Institute of Science and Technology

Prashant Kumar, University of Minnesota Twin Cities

Albert Liu, Massachusetts Institute of Technology

Akanksha Menon, Georgia Institute of Technology

Akinola Oyedele, Oak Ridge National Laboratory

Jessica Swallow, Massachusetts Institute of Technology

Elizabeth Tennyson, University of Maryland

Yu Tian, University of Delaware

Chen Wang, University of California, Los Angeles

Wennie Wang, University of California, Santa Barbara

Yiping Wang, Rensselaer Polytechnic Institute

Shuya Wei, Cornell University

Rong Ye, University of California, Berkeley

Hyojin Yoon, Pohang University of Science and Technology


MIT Museum

A visit to Boston could not be complete without paying a visit to the MIT Museum. It is a highly interactive museum and a heaven for science lovers. 

It takes you back in time where innovation began to speed up and brings you 'back to the future'. There are demonstrations of mechanical parts (see the video) in action. There is a souvenir shop as well where you embrace your geeky side of personality and purchase amazing t-shirts, watches and Einstein's model. 

 

 

 

 

 

Follow me on Twitter: @rahim_munir1

I blog at "Succinct Monograph"

 

 


Symposium X—Frontiers of Materials Research

F17_Thursday_SympX_250x250Nam-Gyu Park, Sungkyunkwan University

History, Progress and Perspective of Halide Perovskite Photovoltaics

Written by Arthur L. Robinson

In his Symposium X presentation, Nam-Gyu Park of Sungkyunkwan University placed perovskite photovoltaics squarely in the category of a disruptive technology, which he defined as one that replaces an existing technology. He cited the example of Kodak, which filed for bankruptcy in 2012 after dominating the analog film business for much of its 131 years of existence, owing to its unwillingness to pursue digital technology after its 1975 invention of the digital camera. Drawing on a 1962 theory of the diffusion of innovation, Park showed that there is a period of discontinuity marked by a transition state during which the old technology matures and then declines while the new one is in an innovation stage. In the auto industry, we are seeing the hybrid gasoline/battery vehicle as a transition to the electric vehicle, and in renewable energy, where the solar disruption has already begun, the replacement of silicon by perovskite photovoltaics, owing to superb performance and very low cost, will be marked by tandem silicon/perovskite solar cells.

Reviewing perovskite basics, Park first recalled the structure of an ABX3 perovskite (an isostructure of the orthorhombic MgTiO3 mineral found in the Earth’s lower mantle) then moved on to the organic-lead halide perovskites, APbI3, where in this talk the A is usually CH3NH3 (methylammonium or MA). Park cautioned that nanocrystals of these materials are vastly different from conventional semiconductor nanocrystals, such as CdSe and InP, in part because of the highly delocalized iodide cation. One difference is the defect tolerance of lead halide perovskites that is due to the bandgap being formed from two sets of antibonding orbitals, as opposed to bonding and antibonding states in conventional semiconductors, and therefore resulting in shallow, less damaging rather than damaging mid-gap states for defects.

Park then switched to a quick history of the perovskite solar cell (PSC), beginning with the 2009 report from Tsutomo Miyasaka’s group at Toin University of Yokohama of perovskite-sensitized solar cells consisting of MAPbBr3 or MAPbI3 nanocrystals coating an 8-µm-thickTiO2 layer, with the iodide version showing a power conversion efficiency of 3.8%. This was followed in 2011 by a report from Park’s group, which had raised the power conversion efficiency to 6.5%. One reason for the advance was a more concentrated precursor solution, which promoted the formation of favorable PbI6–4 and one-dimensional Pb2I4 colloids. A further development published by Park’s group in 2012 was based on decreasing the TiO2 film thickness to less than 1 µm and infiltrating the film pores with an organic hole-conducting polymer (Spiro meOTAD) to achieve a power conversion efficiency of 9.7%. This publication was followed by a rapid increase in the number of perovskite solar cell publications from a few to more than 2000 in 2016. Noting a similarity to the rapid increase in graphene publications that culminated in a Nobel Prize, Park humorously wondered what the future held in store for perovskite researchers. He also noted a subsequent increase in perovskite solar cell power conversion efficiencies, now at 22.7%. An analysis of publications and patents suggested five emerging research areas: perovskite fundamentals, perovskite solar cells, oxide perovskites, perovskite tandem photovoltaics, and perovskite light-emitting diodes (LEDs).

From here, Park looked at recent progress in perovskite solar cell research. In brief, among these were controlling the crystal size for high efficiency, use of an adduct synthesis approach (the addition of two or more distinct molecules resulting in a single reaction product containing all the atoms of all the components) for reproducibility, passivation of grain boundaries for longer carrier lifetime, substitution of formamidinium [HC(NH2)2] for methylammonium for high power conversion efficiency and photostability, the addition of a small amount of cesium to the formamidinium for resistance to humidity and reduced hysteresis in the I-V curve, and the synthesis of nanowires with improved lateral conductivity and carrier lifetime. Park also described a method for reduction in hysteresis and improving moisture stability by means of interfacial nanoengineering using a two-dimensional perovskite of the form A2PbI4, where A is phenethylamine or PEA, at the boundaries between the three-dimensional crystals.

Taking a wider view of possible perovskite applications, Park reported on efforts in his group to make LEDs, based on a nonstoichiometric adduct method and solvent-vacuum drying process. The researchers achieved an emission quantum efficiency of 8.2%. Park finished with an even bigger leap to x-ray imaging of humans, where repeated medical x-ray exposure can accumulate over time to reach cancer-causing doses. A direct imaging camera based on multicrystalline perovskite crystals was constructed and in tests achieved clear images at lower doses than existing amorphous selenium arrays.

Park summarized his talk with these points:

  1. Grain size with dominant radiative-recombination is important for high efficiency PSC.
  2. Grain boundary engineering is important not only for high efficiency but also for stability.
  3. Compositional engineering is important for structural stability and device stability.
  4. Understanding precursor solution chemistry is important for high quality perovskite films.
  5. Understanding defect chemistry and defect engineering are important for hysteresis-free PSC.
  6. Organic-inorganic lead halide perovskites are (and will be) game changers not only in photovoltaics but also in diverse optoelectronic applications.

Symposium X—Frontiers of Materials Research features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.


MRS Medal/ Symposium X—Frontiers of Materials Research

F17_Thursday_Medal-Xia_250x250Younan Xia, Georgia Institute of Technology

Towards Affordable and Sustainable Use of Precious Metals in Catalysis and Medicine

Towards Predictable and Deterministic Synthesis of Colloidal Metal Nanocrystals

Written by Aditi Risbud

On Thursday evening, Younan Xia of the Georgia Institute of Technology was honored with the MRS Medal for “seminal contributions to shape-controlled synthesis of metal nanocrystals with major impact on catalysis, plasmonics and biomedicine.”

Xia’s group has invented myriad nanomaterials for applications in catalysis, plasmonics, electronics, display, energy, and medicine. His silver nanowire technology is an integral component of flexible, transparent, and conductive films used in touchscreen displays and flexible electronics. He has received many prestigious awards, including the ACS National Award in the Chemistry of Materials, NIH Director’s Pioneer Award, and the NSF CAREER Award.

For his medal talk, Xia discussed precious metals; in particular, platinum and gold. The scarcity, cost, and complex processing of precious metals, he suggested, means scientists need to develop a way to use precious metals in a sustainable fashion.

Using the structure of graphene as inspiration, other researchers have mimicked the unique features of graphene in metal nanosheets. Xia’s team has built upon this to develop platinum nanocages for catalysis and gold nanocages that can be used for medical imaging.

“We believe this will be the future direction if you really want to scale up for large-volume production of nanomaterials,” Xia said. “Hopefully in the future we can have hollow and porous nanocrystals that can help us to cut the cost and achieve sustainable use of all the precious metals.”

Xia also gave a Symposium X talk on Tuesday afternoon about the synthesis of colloidal metal nanocrystals. In the early 2000s, Xia said, nanomaterials had a great deal of polydispersity—no two particles had the same size, or shape, or structure. To be used successfully in any applications, the size and the morphology of nanostructures must be controlled. Now, after nearly two decades of studying the nucleation and growth of colloidal nanocrystals, Xia’s research team can reliably synthesize a wide range of metal nanocrystals with controlled nucleation and growth.  

In particular, Xia noted, symmetry reduction is always involved in nanocrystal synthesis and can be used to control the final morphology of nanocrystals. By studying nanocrystal seeds in solution, and then introducing a precursor that can be reduced at a certain rate constant, the members of his research team are investigating if they can predict if the symmetry is going to be broken, and how it will be broken.  


“Seeded growth could actually become a very powerful pathway for new and diversified nanocrystals,” Xia said. “If you take the seed and if you can control the growth pattern, basically symmetric and asymmetric, even for asymmetric, you have different possibilities, and eventually, you can make nanocrystals with very, very diversified morphologies, and hopefully, they can also have different functionalities to see the different applications.”

The MRS Medal, endowed by Toh-Ming Lu and Gwo-Ching Wang, is awarded for a specific outstanding recent discovery or advancement that has a major impact on the progress of a materials-related field. Symposium X lectures are aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.


MRS Medal

F17_Thursday_Medal-Aizenberg_250x250Joanna Aizenberg, Harvard University

EVERYTHING SLIPS—Design of Novel Non-Fouling Materials

Written by Aditi Risbud

On Thursday evening, Joanna Aizenberg of Harvard University gave the first of two MRS Medal lectures. Aizenberg pursues multidisciplinary research that includes biomimetics, crystal engineering and smart materials. She was honored for “developing new synthesis routes inspired by biological principles for the fabrication of advanced, complex, multifunctional materials and devices.”

Aizenberg is a prominent scientist in the field of biologically-inspired materials research, and has been elected to the American Academy of Arts & Sciences, American Philosophical Society, American Association for the Advancement of Science, and as a Fellow of the Materials Research Society and of the American Physical Society. In addition to her many honors, she also introduced the popular “Science as Art” feature to MRS meetings.

In her talk, she noted everything—from snow to arteries to solar panels—gets dirty. Despite scientists’ efforts to create new materials and devices, dirt compromises the function of anything created in the laboratory. Therefore, new approaches are needed to develop non-fouling materials. Superhydrophobic surfaces inspired by lotus leaves and butterflies can provide a way to tackle the dirt by repelling water, but they are limited when translated to real-world situations.

Recently, Aizenberg’s team developed slippery liquid-infused porous surfaces, or SLIPS, based on structures found in fish and carnivorous plants. These engineered surfaces allow a near-frictionless surface to be formed in all materials types, in any shape, and at any scale. What’s more, these surfaces can be used in various environments, including at high and low temperatures and underwater.

“In just six years, we are now capable of creating these surfaces in all material types, we can make them mechanically robust, and we are beginning to understand the mechanisms of how these materials work,” Aizenberg said. “It’s just the tip of the iceberg, and many interesting things can be done with this approach.”

The MRS Medal, endowed by Toh-Ming Lu and Gwo-Ching Wang, is awarded for a specific outstanding recent discovery or advancement that has a major impact on the progress of a materials-related field.