Researchers Seek Better Fabrication Techniques for pH-Responsive Microcapsules

Scanning electron micrographs of intact, left, and ruptured microcapsules with a polymeric shell wall and an aqueous core. Images courtesy of University of Illinois at Urbana-Champaign.

Researchers at the University of Illinois at Urbana-Champaign (Champaign, Illinois, USA) have developed a new method to create microcapsules, which they describe as tiny droplets surrounded by a solid shell. The technique can be used to make microcapsules that respond to changes in pH, which are useful for applications such as anticorrosion coatings.1

“There are a number of ways that have been used to make microcapsules,” says Nancy Sottos, head of the school’s materials science and engineering department. “However, those methods are tedious, slow, and they clog the devices. Additionally, the capsules are not the same size.”

Emulsion Templates

The new technique, developed by members of the university’s autonomous materials systems group, involves using emulsion templates to make the microcapsules. “It’s like making a salad dressing,” says Sottos, who leads the group. “You slowly mix in the oil to the water. The faster you mix, the smaller the droplets. Then you form a shell wall around the emulsion droplets.”

In their work, the researchers used a needle containing capillary tubes inside it. The liquid core of the microcapsule enters through a central tube, and the shell material comes through an outer tube. The needle vibrates uniformly across the surface of water.

When the needle crosses the surface, the droplets are detached from the capillary tubes, forming uniformly-sized emulsion droplets for microcapsules. “This technique gives you control over the shell thickness, the core volume, and the overall size of the capsule,” says Dhawal Thakare, a doctoral candidate and graduate student within the group. “Our technique is simple and can be assembled very easily in a lab environment.”

pH-Responsive Capsules

Using this technique, the researchers say they have made pH-responsive capsules that can break open when there is a pH change in the environment. “Drug delivery often uses pH changes to release the capsule contents,” Sottos says. “We were interested in using them to encapsulate anticorrosive agents. When the pH changes, the microcapsules open up and release the anti-corrosive agents.” “Although the technique gives you precise control over the microcapsules, it is hard to make capsules that are very small,” Thakare adds. “Another disadvantage is that you are introducing fluids through capillaries. As the viscosity of the fluid increases, the pressure increases, and there are higher chances of not attaining an unobstructed flow."

Moving forward, the researchers are interested in expanding the range of materials that they can encapsulate, as well as improving the technique so that they can make smaller microcapsules.

Funding for the Study

The study was funded by the BP International Center for Advanced Materials (ICAM). ICAM is a partnership between The University of Manchester, the University of Cambridge, Imperial College London, and the University of Illinois at Urbana-Champaign. ICAM was set up by BP (London, United Kingdom) in late 2012 with a $100 million investment, with a goal of bringing together the strengths of four world-class universities and BP’s expertise in energy to create an international hub of excellence in advanced materials research. Researchers within the center are focused on structural materials, corrosion, separations, surfaces, deposits, imaging, modeling, and self-healing materials.

Source: Illinois Mechanical Science and Engineering,


1 “Developing Better Fabrication Techniques for pH-Responsive Microcapsules,” Illinois Mechanical Science and Engineering News & Events, June 11, 2020, (August 18, 2020).

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