MMaterialsgateNEWS 2017/12/21

Particle size matters for porous building blocks

Credit: Courtesy of the Multiscale Materials Laboratory

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.

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.

Source: Rice University – 18.12.2017.

Investigated and edited by:

Dr.-Ing. Christoph Konetschny, Inhaber und Gründer von Materialsgate
Büro für Material- und Technologieberatung
The investigation and editing of this document was performed with best care and attention.
For the accuracy, validity, availability and applicability of the given information, we take no liability.
Please discuss the suitability concerning your specific application with the experts of the named company or organization.

You want additional material or technology investigations concerning this subject?

Materialsgate is leading in material consulting and material investigation.
Feel free to use our established consulting services

MMore on this topic

Credit: American Chemical Society

ACS Applied Materials & Interfaces:

Inspired by the varying colors that gleam off of beetle shells, scientists have developed color-shifting nanoparticles that can change hue even after being embedded into a material. A report on the new, inexpensive technique, which could lead to the production of easier-to-read sensors and anti-tampering tags, appears in ACS Applied Materials & Interfaces. The shells, or exoskeletons, of beetles are covered with stacks of crystalline-like shapes that scatter light and produce dazzling colors. In some cases, these colors can change with just a slight shift of the viewing angle. Known as structural colors, scientists have long been interested in replicating them for use in paints, dyes... more read more

When oil mixes with or enters into water, conventional methods of cleaning the water and removing the oil can be challenging, expensive and environmentally risky.

But researchers in the Cockrell School of Engineering at The University of Texas at Austin believe they may have developed a better method. In a study published this spring in the Journal of Nanoparticle Research, the researchers used magnetic nanoparticles to separate oil from water through a simple process that relies on electrostatic force and a magnet. The engineers believe their new technique could improve water treatment for oil and gas production, more efficiently clean up oil spills and potentially remove lead from drinking water. Today, nanoparticles, which are tiny particles that can be coated with different chemicals such as polymers, are used in a wide variety of areas and... more read more

Polymer nanocomposites mix particles billionths of a meter (nanometers, nm) in diameter with polymers, which are long molecular chains.

Often used to make injection-molded products, they are common in automobiles, fire retardants, packaging materials, drug-delivery systems, medical devices, coatings, adhesives, sensors, membranes and consumer goods. When a team led by the Department of Energy's Oak Ridge National Laboratory tried to verify that shrinking the nanoparticle size would adversely affect the mechanical properties of polymer nanocomposites, they got a big surprise. "We found an unexpectedly large effect of small nanoparticles," said Shiwang Cheng of ORNL. The team of scientists at ORNL, the University of Illinois at Urbana-Champaign (Illinois) and the University of Tennessee, Knoxville (UTK) reported... more read more

Scientists distinguished how protein 'corona' of silver nanoparticles affects their cellular toxicity

A senior fellow at the Faculty of Chemistry, MSU, Vladimir Bochenkov together with his colleagues from Denmark succeeded in deciphering the mechanism of interaction of silver nanoparticles with the cells of the immune system. The study is published in the journal Nature Communications. 'Currently, a large number of products are containing silver nanoparticles: antibacterial drugs, toothpaste, polishes, paints, filters, packaging, medical and textile items. The functioning of these products lies in the capacity of silver to dissolve under oxidation and form ions Ag+ with germicidal properties. At the same time there are research data in vitro, showing the silver nanoparticles toxicity... more read more

MaterialsgateNEWSLETTER

Partner of the Week

Search in MaterialsgateNEWS

Books and products

MaterialsgateFAIR:
LET YOURSELF BE INSPIRED