Rice University scientists find porous nanoparticles get tougher under pressure, but not when assembled
Porous particles of calcium and silicate show potential as building blocks for a host of applications like self-healing materials, bone-tissue engineering, drug delivery, insulation, ceramics and construction materials, according to Rice University engineers who decided to see how well they perform at the nanoscale.
Thin (left) and thick films made of porous nanoparticles of calcium and silicate reacted differently under pressure as tested in a Rice University lab. Particles in the thin films moved out of the way for a nanoindenter and allowed the film to stay intact, while thick films cracked.
Credit: Multiscale Materials Laboratory/Rice University
Following previous work on self-healing materials using porous building blocks, Rice materials scientist Rouzbeh Shahsavari and graduate student Sung Hoon Hwang made a wide range of porous particles between 150 and 550 nanometers in diameter -- thousands of times smaller than the thickness of a sheet of paper -- with pores about the width of a strand of DNA.
They then assembled the particles into micron-sized sheets and pellets to see how well the arrays held up under pressure from a nanoindenter, which tests the hardness of a material.
The results of more than 900 tests, reported this month in the American Chemical Society's ACS Applied Materials and Interfaces, showed that bigger individual nanoparticles were 120 percent tougher than smaller ones.
This, Shahsavari said, was clear evidence of an intrinsic size effect where particles between 300 and 500 nanometers went from brittle to ductile, or pliable, even though they all had the same small pores that were 2 to 4 nanometers. But they were surprised to find that when the same big particles were stacked, the size effect didn't carry over entirely to the larger structures.
The principles revealed should be important to scientists and engineers studying nanoparticles as building blocks in all kinds of bottom-up fabrication.
"With porous building blocks, controlling the link between porosity, particle size and mechanical properties is essential to the integrity of the system for any application," Shahsavari said. "In this work, we found there is a brittle-to-ductile transition when increasing the particle size while keeping the pore size constant.
"This means that larger submicron calcium-silicate particles are tougher and more flexible compared with smaller ones, making them more damage-tolerant," he said.
The lab tested self-assembled arrays of the tiny spheres as well as arrays compacted under the equivalent of 5 tons inside a cylindrical press.
Four sizes of spheres were allowed to self-assemble into films. When these were subject to nanoindentation, the researchers found the intrinsic size effect largely disappeared as the films showed variable stiffness. Where it was thin, the weakly bonded particles simply made way for the indenter to sink through to the glass substrate. Where it was thick, the film cracked.
"We observed that the stiffness increases as a function of applied indentation forces because as the maximum force is increased, it leads to a greater densification of the particles under load," Shahsavari said. "By the time the peak load is reached, the particles are quite densely packed and start behaving collectively as a single film."
Pellets made of compacted nanospheres of various diameters deformed under pressure from the nanoindenter but showed no evidence of getting tougher under pressure, they reported.
"As a next step, we're interested in fabricating self-assembled superstructures with tunable particle size that better enable their intended functionalities, like loading and unloading with stimuli-sensitive sealants, while offering the best mechanical integrity," Shahsavari said.
The National Science Foundation supported the research.
Read the abstract at http://pubs.
This news release can be found online at http://news.
Follow Rice News and Media Relations via Twitter @RiceUNews
Biomimetic, strong, tough and self-healing composites using universal sealant-loaded, porous building blocks: http://pubs.
Multiscale Materials Laboratory (Shahsavari Lab): http://rouzbeh.
George R. Brown School of Engineering: http://engineering.
Rice Department of Civil and Environmental Engineering: http://www.
Rice Department of Materials Science and NanoEngineering: https:/
Images for download:
Thin (left) and thick films made of porous nanoparticles of calcium and silicate reacted differently under pressure as tested in a Rice University lab. Particles in the thin films moved out of the way for a nanoindenter and allowed the film to stay intact, while thick films cracked. (Credit: Multiscale Materials Laboratory/Rice University)
Rice University materials scientists tested structures made of calcium-silicate nanoparticles and found that particles go from brittle to ductile as they increase in size. The compressed single particle at left deformed under the pressure of a nanoindenter. At center and right, large particles did not crack under pressure. (Credit: Multiscale Materials Laboratory/Rice University)
Rice University materials scientists synthesized spherical, porous nanoparticles of calcium and silicate, formed films and pellets and tested their toughness under pressure from a nanoindenter. They found films made of larger particles approaching 500 nanometers were much tougher and the films and pellets less prone to cracking under pressure. At right, small particles are deformed after nanoindentation. (Credit: Multiscale Materials Laboratory/Rice University)
Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,879 undergraduates and 2,861 graduate students, Rice's undergraduate student-to-faculty ratio is 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for quality of life and for lots of race/class interaction and No. 2 for happiest students by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to http://tinyurl.
Editor's note: Links to high-resolution images for download appear at the end of this release.
David Ruth | EurekAlert!
Barely scratching the surface: A new way to make robust membranes
13.12.2018 | DOE/Argonne National Laboratory
Topological material switched off and on for the first time
11.12.2018 | ARC Centre of Excellence in Future Low-Energy Electronics Technologies
The more objects we make "smart," from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.
Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved...
What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...
A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.
The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...
A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.
Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...
Over the last decade, there has been much excitement about the discovery, recognised by the Nobel Prize in Physics only two years ago, that there are two types...
12.12.2018 | Event News
10.12.2018 | Event News
06.12.2018 | Event News
14.12.2018 | Power and Electrical Engineering
14.12.2018 | Physics and Astronomy
14.12.2018 | Physics and Astronomy