Plenary Session Featuring the Fred Kavli Distinguished Lectureship in Materials Science

IMG_8542_800x800Sharon C. Glotzer, University of Michigan

Engineering Matter Across Scales

Written by Arthur L. Robinson

The ability to design and make the perfect material with just the right properties to do what we want, how we want, and when we want is the holy grail of materials research says Sharon Glotzer of the University of Michigan. Such “materials on demand” require control over thermodynamics, kinetics, nonequilibrium behavior and structure across many length and timescales. In her Fred Kavli Distinguished Lecture in Materials Science during Monday evening’s Plenary Session, Glotzer took it upon herself to demonstrate how atomic and molecular crystal structures—made possible by chemical bonds at Angstrom scales—can be realized with noninteracting nanoparticles and colloids via entropic bonds at nanometer to micron scales. Beyond their importance in understanding and engineering the self-assembly of colloidal crystals and nanoparticle superlattices, Glotzer says, the fact that some of the most complex structures in metallurgy and in molecular crystals can be realized without explicit attraction of any kind, reveals fundamental insights into what is needed to engineer matter across scales.

Physical matter is held together by chemical bonds (ionic, covalent, hydrogen, metallic, and so on). It is a combination of quantum theory, which describes interatomic interactions, and statistical thermodynamics, which governs free-energy minimization, that determine all possible crystal structures in nature. Stable crystals can be predicted if we know all the interatomic forces and can minimize the free energy subject to thermodynamic constraints. In principle, the chemical bonding structure of any set of N atoms can be computed, with varying degrees of accuracy depending on the approximations used.

Shifting to soft matter, Glotzer explains that the entities playing the role of “atoms,” being big and complex, are different. Examples are dendrimers molecular, DNA, proteins, micelles, nanoparticles, including those functionalized with ligands, and viruses. Scores of three-dimensional crystal structures can self-assemble in solution from soft-matter building blocks. Most are isostructural to atomic crystals, though with larger lattice spacings. In every case, interparticle interactions combined with thermodynamics dictate crystal morphologies.

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Particle shape plays a big role in dictating colloidal crystal structure because the anisotropy can create an effective “valence” that dictates the number and bond orientation of neighboring particles. Clathrates, structures consisting of polyhedral cages with large pores that can be used for host-guest chemistry, represent a challenging target for colloidal assembly. Here, particles of sizes ranging from a few nanometers to a couple of microns self-assemble in solution to form crystals where the “atoms” are replaced by particles made of atoms. Typically these particles are metals like Au or Ag, semiconductors like CdTe or CdS, or polymer like PS or PMMA, and functionalized with molecular organic ligands or DNA. The particles can be charged or neutral, be magnetic or not, spherical or rod-like or polyhedral. Particles can interact via electrostatic interactions mediated by the solvent, van der Waals interactions, magnetic dipole interactions, h-bonds between ligands, and excluded-volume interactions.  Regardless of what interactions are present, they conspire to produce net interparticle repulsion and attraction that—combined with thermodynamics—dictate the preferred arrangement of particle positions and orientations. Today these colloidal crystals can be predicted, designed, and synthesized.

Very counterintuitive, says Glotzer, is that even in the absence of any explicit interparticle interactions, colloidal particle can form crystals due solely to particle shape and excluded-volume interactions. In these cases, free energy minimization is the same thing as entropy maximization. Entropy alone can drive self-assembly of an incredible diversity of colloidal crystal structures and with extraordinary complexity, both with and without atomic or molecular analogues. Upon crowding, hard particles organize to maximize the system entropy by maximizing the number of allowed microstates. Lots of questions remain: What else is possible with entropy alone? What crystals structures are not possible with entropy alone; if not, why not? What about multi-atomic systems of shapes that are not necessarily hard? To what extent is entropy helping to order nanoparticles into colloidal crystals? Can we engineer entropy to engineer target crystals?

Finishing up, Glotzer described entropic bonding as a process that selects for the set of interparticle orientations and positions that maximizes system entropy in analogy with chemical bonding as a process that selects for the set of interatomic orientations and positions that minimizes the total energy among atoms. In this analogy, entropy creates an emergent “valence.” With an entropic analog to the Schrödinger equation based on “shape orbitals” that can be placed on a lattice and optimized for maximum overlap to find the bonding orbital and free energy of a unit cell, Glotzer and colleague Thi Vo developed a predictive microscopic theory of entropic bonding based on a pseudopotential between a quasiparticle and a hard shape. They replaced the electron probability density (wave function) in the Schrödinger equation with the quasiparticle probability density, where quasiparticles serve as a proxy for an effective entropic attraction between shapes in a Schrödinger-like equation. Applying their theory to a hard-shape system of two hard cubes in a box at a density of 0.55, they found their model predicted a simple cubic “lattice” that would have lower energy than fcc or bcc, whereas for a system of truncated tetrahedra, the preferred lattice would progress from that of a quasicrystal to diamond to -Sn to bcc as the degree of truncation increases. These predictions match those from molecular-assembly simulations made in 2012.

For takeaways, Glotzer noted that entropic forces can be directional, effect valence, and act as bonds; there is now a predictive microscopic theory of entropic bonds; and this allows the use of approaches used for atomic crystals to be used for colloidal crystals.

The Kavli Foundation is dedicated to advancing science for the benefit of humanity, promoting public understanding of scientific research and supporting scientists and their work.


Best Poster Award Winners – Monday

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Juyeol Bae, Ulsan National Institute of Science and Technology

SB11.03.04 Microfluidic Patterning of Liquid-Mediated Materials through Liquid Foam Control

 

Andrea Diaz-Gaxiola, University of Bristol

SB04.03.01 Fabricating Tough and Elastic Photo-Actuating Hydrogel Fibres

 

Sunghoon Kim, Ajou University, LG Innotek

EN16.03.09 Ultrasensitive and Highly Stable Humidity Sensor Using Cesium Lead Halide Perovskite/Ceramic Nanocomposite Films 

 

Mikhail Shalaginov, Massachusetts Institute of Technology

EL04.05.01 Chalcogenide Alloys Enable Reconfigurable All-Dielectric Metasurfaces

 

Jiaqi Ma, Huazhong University of Science and Technology

EN09.03.12 Chiral 2D Perovskites with a High Degree of Circularly Polarized Photoluminescence

 


United Nations Sustainable Development Goals Workshop—Agents for Sustainable Community Change

Typically thoughts about sustainability and materials lands on research in solar cells and batteries. However, this workshop demonstrated that the role played by materials researchers can be so much more.

The goal of the workshop on the UN sustainable development goals (SDGs) was to help participants learn how to plan action to incorporate solutions to the SDGs within their own institutions.

Allison Paradise, CEO and founder of My Green Lab, presented examples of how individual researchers spear-headed movements at their institutions to build a culture of sustainability through science – which is the mission of her company.

Peter Buckland of The Pennsylvania State University (PSU) described the multi-year process it took for PSU to embed the mission to combat climate change within the university’s strategic policy. He pointed to the work of students networking with faculty and staff to drive this initiative.

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Vasiliki Kioupi of Imperial College London introduced the history and current status of the UN SDGs and Ashley White of Lawrence Berkeley National Laboratory gave examples of sustainable development of the materials themselves. Through further discussions in break-out groups, participants mapped the SDGs over materials research. For example, to combat hunger (SDG #2), materials used for fertilizers can be mixed with components added to the soil to prevent fertilizers from washing away, which would be less wasteful and ultimately less costly for agriculture.

In the last activity of the afternoon, participants discussed projects they could design within their home institutions, whether it be changes in the curriculum, in research, or community engagement that feature several of the SDGs.

The workshop was sponsored in part by Focus on Sustainability, Los Alamos National Laboratory, ReACT, NSF, and PPG.


Armin VahidMohammadi: Three-time winner of Science as Art

In Materials Connect, blogger Tianyu Liu of Virginia Tech interviews Armin VahidMohammadi of Auburn University about his experience with digital art.It is the third time Armin wins, and he is the only graduate student who achieves this hat trick as the first and leading author of the artwork,” Liu writes, referring to the MRS Science as Art competition. Liu writes:

“Armin, and his brother, Aidin, managed to teach themselves how to work with different 3D software by reading the manuals and instructions of them. ‘Aidin was so passionate in 3D artworks and we always were discussing new things. I am sure we could never do what we can do today without learning and working together,” Armin says.” Read more 

 

MXene turtle

(Credit: Courtesy of Armin VahidMohammadi at Auburn University, U.S., and the Materials Research Society)

A colored SEM image of a 2D V2CTx particle showing similarities to the head of an imaginary giant turtle. V2CTx is synthesized by selective etching Al atoms from V2AlC and is a promising electrode material for energy-storage devices.


Thank you!

The 2019 MRS Spring Meeting & Exhibit came to a successful conclusion on Friday, April 26, with materials researchers and exhibitors gathered from around the world.

Our congratulations go to Meeting Chairs Yuping Bao, Bruce Dunn, Subodh Mhaisalkar, Subhash L. Shindeand Ruth Schwaiger for putting together an excellent technical program along with various special events. MRS would also like to thank all the Symposium Organizers, Session Chairs, and Symposium Assistants for their part in the success of this meeting. A thank you goes to the Exhibitors, Symposium Support, and to the sponsors of the special events and activities.

Contributors to news on the 2019 MRS Spring Meeting & Exhibit include Meeting Scene reporters Chiung-Wei Huang (@CWHuang14), Gargi Joshi, Judy Meiksin (@Judy_Meiksin), Aashutosh Mistry, Don Monroe, Bharati Neelamraju (@Bharati_30), Prachi Patel, Arthur L. Robinson, and Lori Wilson; Bloggers Kony Chatterjee, Dale E. Karas, and Dongwei Sun; and photographers Stephanie Gabborin and Heather Shick; with newsletter production by Karen Colson and Shayla Poling, and newsletter design by Erin Hasinger.

Thank you to MRS Meeting Scene sponsors SPI SuppliesGoodfellow CorporationLake Shore Cryotronics, Inc.Thermo Fisher Scientific; American ElementsRigaku; and MDPI.       

Thank you for subscribing to the MRS Meeting Scene newsletters from the 2019 MRS Spring Meeting & Exhibit. We hope you enjoyed reading them and continue your subscription as we launch into the 2019 MRS Fall Meeting & Exhibit - the conversation already started at #f19mrs! We welcome your comments and feedback.


Mid-Career Researcher Award

Mid Career Researcher Talk_800x533Hongyou Fan, Sandia National Laboratories and The University of New Mexico

Self-Assembly of Functional Nanoscale Materials

Written by Prachi Patel

Hongyou Fan started by graciously thanking his mentors, and his students who “make our science, ideas, and dreams come true, and these are the heroes behind this honor.” He then split his talk into three parts focusing on the pathways he is pursuing in the area of self-assembly of functional nanomaterials.

The first is surfactant-assisted nanoparticle self-assembly and optical coatings. He started by discussing the motivation behind this research. Traditional coating-manufacturing techniques like sputtering and chemical vapor deposition come at a cost, he said. They need vacuum environments, expensive and bulky equipment, and toxic precursors. He wanted to come up with a simple, low-temperature coating process that could be used on delicate substrates, and ideally wanted to use green chemistry. So he decided to make nanoparticles of coating materials, which can be used to make suspensions that can be printed or roll-to-roll coated on large areas.

Fan then detailed the “simple and fast” self-assembly process for making nanoparticles with the help of surfactants. Surfactants are amphiphilic molecules, with hydrophilic heads and hydrophobic tails. In aqueous solutions, the hydrophilic heads connect and create a spherical shell with the hydrophobic tails in the center, forming tiny nanometers-wide micelles.

He and his colleagues start with an oil-based dispersion of metal nanocrystals. The particles are functionalized with organic ligands, which keep them separate and make them hydrophobic. By mixing the nanoparticles into an aqueous surfactant solution, and then evaporating the solvents, the researchers get nanoparticle-micelles dispersed in water. Fan showed that he has made nanoparticle-micelles using various materials—metals, semiconductors, and perovskites—and of different shapes and sizes. Then, using processes such as dip-coating and inkjet printing, he can use the nanoparticle-micelles to make optical coatings with tunable properties.

Fan then moved on to the second part of his talk. This involves the use of the surfactant-enabled self-assembly method to make nanocrystalline superparticles with photoactive molecules. Fan uses porphyrin, an organic molecule in chlorophyll that absorbs sunlight and converts it into energy. Nanocrystalline assemblies of porphyrin could find use in photocatalysis, phototherapy, sensors, and dye-sensitized solar cells, he said.

Adding different functional groups to the ends of porphyrin molecules and changing the pH of the surfactant solution gives self-assembled porphyrin nanostructures of various shapes. Fan showed a gallery of images showing various morphologies and dimensions of nanocrystals like one-dimensional (1D) rods and wires, nanodisks, hexagonal rods, and octahedra. He went on to show how redox reactions can be used to deposit platinum on 1D porphyrin nanowires and then the porphyrin can be removed to give hollow platinum shells. Such hollow metallic nanostructures of various shapes could find applications in water splitting, sensors, and phototherapy.

In the last part of his talk, Fan introduced his recent research on pressure-induced nanoparticle assembly, which was inspired by the fast, cost-effective embossing process. “What would happen if we applied pressure to the nanoparticles?” was the question he and his colleagues wanted to answer.

So they sandwiched nanoparticles between diamond tips and applied controlled pressure to them. When gold nanoparticles are compressed like this, they sinter together to form a bundle of nanowires of uniform length. But this only happens above a threshold 9 GPa of pressure, Fan has found by studying the nanoparticle assembly under pressure using in situ synchrotron x-ray scattering. At pressures below 9 GPa, particles are forced together but they spring back when the pressure is removed. Depending on the orientation of the original nanocrystals, they can form different dimensional nanostructures. “If you start with 3D particle assemblies you can form interconnected 3D porous structures,” he said.

Fan ended by talking about the importance of MRS in his career. He reminisced about the first meeting he attended as a graduate student, going on to organize symposia and then become meeting chair. Now an MRS Fellow and member of several MRS committees, Fan stated how these engagements have exposed him to new ideas and strategies and meaningful connections. “Overall it supplies tremendous inspiration for my career, research and work,” he said. After this mid-career award, he hopes to continue his research momentum and to serve the MRS community, he said.

The Mid-Career Researcher Award recognizes exceptional achievements in materials research made by mid-career professionals. Endowed by MilliporeSigma.

Fan’s award citation is “for outstanding contributions in nanoparticle self-assembly of functional nanomaterials and for leadership within the materials community.”


Graduate Student Awards

MRS Graduate Student Awards are intended to honor and encourage graduate students whose academic achievements and current materials research display a high level of excellence and distinction. In addition, one student is further recognized with the Arthur Nowick Graduate Student Award which honors the late Dr. Arthur Nowick and his lifelong commitment to teaching and mentoring students in materials science. MRS recognizes the following students of exceptional ability who show promise for significant future achievement in materials research.

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Gold

Zhaoqianqi Feng, Brandeis University

Aristide Gumyusenge, Purdue University (also received the Arthur Nowick Graduate Student Award)

Joon Sang Kang, University of California Los Angeles

Lichen Liu, Universitat Politècnica de València

Hyunwoo Yuk, Massachusetts Institute of Technology

 

Silver

Peter Attia, Stanford University

Amitava Banerjee, Uppsala University

Jennifer Boothby, The University of Texas at Dallas

Wen-Hui Cheng, California Institute of Technology

Hyunjoong Chung, University of Illinois at Urbana-Champaign

Rohit John, Nanyang Technological University

Andrew Meng, Stanford University

Aashutosh Mistry, Purdue University

Rainie Nelson, Iowa State University

Subhajit Roychowdhury, Jawaharlal Nehru Centre for Advanced Scientific Research

Arashdeep Thind, Washington University in St. Louis

Yixiu Wang, Purdue University

Xiaoxing Xia, California Institute of Technology

MRS acknowledges the generous contribution for the Nowick Award to the MRS Foundation from Joan Nowick in memory of her husband Dr. Arthur Nowick.