Georgia Institute of Technology Georgia Institute of Technology

Research Horizons

Georgia Tech's Research Horizons Magazine

More Than Peer Pressure

photo - colloidal crystals

When an assembly of microgel particles includes one particle that’s significantly larger than the rest, that oversized particle spontaneously shrinks to match the size of its smaller neighbors. This self-healing nature of the system allows the microparticles to form defect-free colloidal crystals, an unusual property not seen in systems made up of incompressible particles.

Using small-angle X-ray and neutron-scattering techniques, the researchers carefully studied the structures formed by dense concentrations of the microparticles. They also used tiny piezoelectric pressure transducers to measure osmotic pressure changes in the system. They found that in dense assemblies of microparticles, counter ions bound to the microgels by electrostatic attraction come to be shared by multiple particles, increasing the osmotic pressure which then works to shrink the oversized particle.

“When the particles are close enough together, there is a point at which the cloud of ions can no longer be associated with individual particles because they overlap other particles,” said Alberto Fernandez-Nieves, an associate professor in Georgia Tech’s School of Physics. “The ions create an imbalance between osmotic pressure inside and outside the larger particles, pushing them to de-swell — expel solvent to change size — to match the pressure of the system given by these delocalized ions. This is only possible because the microgel particles are compressible.”

The research was reported in the journal Proceedings of the National Academy of Sciences. — John Toon

photo - Alberto Fernandez Nieves

Alberto Fernandez Nieves is an associate professor in Georgia Tech’s School of Physics.

Subscribe to Research Horizons
Get the latest Georgia Tech research news through our free print magazine, monthly electronic newsletter, and Twitter feed.


Georgia Tech is home to more than 2,500 faculty members who conduct scientific and engineering research in hundreds of different research areas.

Related Stories

Read More
Read More
Read More

Media Contacts

John Toon

John Toon

Director of Research News
Phone: 404.894.6986

Anne Wainscott-Sargent

Research News
Phone: 404-435-5784

Subscribe & Connect

Follow Us on Twitter:


RSS Feeds

Subscribe to our RSS Feeds with your favorite reader.

Email Newsletter

Sign up to receive our monthly email newsletter.

Research Horizons Magazine

Sign up for a free subscription to Research Horizons magazine.