Navigation Links
Entropy can lead to order, paving the route to nanostructures

ANN ARBOR, Mich.Researchers trying to herd tiny particles into useful ordered formations have found an unlikely ally: entropy, a tendency generally described as "disorder."

Computer simulations by University of Michigan scientists and engineers show that the property can nudge particles to form organized structures. By analyzing the shapes of the particles beforehand, they can even predict what kinds of structures will form.

The findings, published in this week's edition of Science, help lay the ground rules for making designer materials with wild capabilities such as shape-shifting skins to camouflage a vehicle or optimize its aerodynamics.

Physicist and chemical engineering professor Sharon Glotzer proposes that such materials could be designed by working backward from the desired properties to generate a blueprint. That design can then be realized with nanoparticlesparticles a thousand times smaller than the width of a human hair that can combine in ways that would be impossible through ordinary chemistry alone.

One of the major challenges is persuading the nanoparticles to create the intended structures, but recent studies by Glotzer's group and others showed that some simple particle shapes do so spontaneously as the particles are crowded together. The team wondered if other particle shapes could do the same.

"We studied 145 different shapes, and that gave us more data than anyone has ever had on these types of potential crystal-formers," Glotzer SAID. "With so much information, we could begin to see just how many structures are possible from particle shape alone, and look for trends."

Using computer code written by chemical engineering research investigator Michael Engel, applied physics graduate student Pablo Damasceno ran thousands of virtual experiments, exploring how each shape behaved under different levels of crowding. The program could handle any polyhedral shape, such as dice with any number of sides.

Left to their own devices, drifting particles find the arrangements with the highest entropy. That arrangement matches the idea that entropy is a disorder if the particles have enough space: they disperse, pointed in random directions. But crowded tightly, the particles began forming crystal structures like atoms doeven though they couldn't make bonds. These ordered crystals had to be the high-entropy arrangements, too.

Glotzer explains that this isn't really disorder creating orderentropy needs its image updated. Instead, she describes it as a measure of possibilities. If you could turn off gravity and empty a bag full of dice into a jar, the floating dice would point every which way. However, if you keep adding dice, eventually space becomes so limited that the dice have more options to align face-to-face. The same thing happens to the nanoparticles, which are so small that they feel entropy's influence more strongly than gravity's.

"It's all about options. In this case, ordered arrangements produce the most possibilities, the most options. It's counterintuitive, to be sure," Glotzer said.

The simulation results showed that nearly 70 percent of the shapes tested produced crystal-like structures under entropy alone. But the shocker was how complicated some of these structures were, with up to 52 particles involved in the pattern that repeated throughout the crystal.

"That's an extraordinarily complex crystal structure even for atoms to form, let alone particles that can't chemically bond," Glotzer said.

The particle shapes produced three crystal types: regular crystals like salt, liquid crystals as found in some flat-screen TVs and plastic crystals in which particles can spin in place. By analyzing the shape of the particle and how groups of them behave before they crystallize, Damasceno said that it is possible to predict which type of crystal the particles would make.

"The geometry of the particles themselves holds the secret for their assembly behavior," he said.

Why the other 30 percent never formed crystal structures, remaining as disordered glasses, is a mystery.

"These may still want to form crystals but got stuck. What's neat is that for any particle that gets stuck, we had other, awfully similar shapes forming crystals," Glotzer said.

In addition to finding out more about how to coax nanoparticles into structures, her team will also try to discover why some shapes resist order.

Contact: Nicole Casal Moore
University of Michigan

Related biology technology :

1. En route to a quantum computer
2. 3-dimensional view of 1-dimensional nanostructures
Post Your Comments:
(Date:11/30/2015)... Md. , Nov. 30, 2015 ... development company committed to the fostering and monetization ... the current and prospective initiatives designed to create ... Chief Executive Officer of Spherix. "Based on published ... future licensees exceeds $50 billion and Spherix will ...
(Date:11/30/2015)... , Nov. 30, 2015  Champions Oncology, Inc. (CSBR), ... services to personalize the development and use of oncology ... Executive Officer, will be presenting at the LD MICRO ... Pacific Standard Time (PST).  The conference, held at the ... Angeles, CA , will feature 200 small/micro-cap companies ...
(Date:11/30/2015)... 30, 2015 TapImmune, Inc. ... of innovative peptide and gene-based immunotherapeutics and vaccines for ... it will be presenting at the 8 th ... at 2.30 PM PT. Dr. John N. Bonfiglio ... be giving the presentation and will join TapImmune management ...
(Date:11/30/2015)... , Nov. 30, 2015  Aytu BioScience, Inc. (OTCQB: ... and related conditions, will present at two upcoming investor ... an interactive real-time virtual conference, to be held December ... Conference, to be held December 2 nd & ... and streamed live via webcast. ...
Breaking Biology Technology:
(Date:11/17/2015)... , November 17, 2015 ... au 19 novembre  2015.  --> Paris ... --> DERMALOG, le leader de l,innovation biométrique, ... la fois passeports et empreintes sur la même surface ... les passeports et l,autre pour les empreintes digitales. Désormais, ...
(Date:11/12/2015)... CAMBRIDGE, Mass. , Nov. 12, 2015 /PRNewswire/ ... Broad Institute of MIT and Harvard for use ... chemical discovery information management tools. The partnership will ... share both biological and chemical research information internally ... tools will be used for managing the Institute,s ...
(Date:11/9/2015)... , Nov. 09, 2015 ... addition of the "Global Law Enforcement ... offering. --> ) has ... Law Enforcement Biometrics Market 2015-2019" report ... and Markets ( ) has announced ...
Breaking Biology News(10 mins):