Researchers have made a breakthrough in the development of nanoparticles that can improve future fabrication of emulsion materials, paving the way for more durable firefighting operations or novel controlled-release medications.
A team at Texas A&M University has found a way to control as well as switch the charge of nanoparticles on a two-fluid interface—specifically, oil and water--to create a more stable system.
This capability results in a surface for emulsion materials— a mixture of two or more incompatible and unmixable liquids that are stabilized by the interference of solid particles—that can change dynamically depending on the application.
“Based on this idea, we proposed a concept that this will be a pH-responsive material,” explained Qingsheng Wang, associate professor in the Artie McFerrin Department of Chemical Engineering at Texas A&M, in a press statement. “If we change the pH value, we can control the molecular diffusion.”
The emulsion is made possible by a process called Pickering emulsion, in which solid particles interfere with the unmixable liquids and tightly assemble at the fluid-fluid interface to prevent coalescence.
The key to achieving success in the work was the use of graphene quantum dots (GQDs) containing zwitterionic properties to stabilize the emulsion, researchers said. Materials with zwitterionic properties create stable, separated unit electrical charges on atoms. Researchers stacked the GQDs together in sheets less than 5 nanometers thick—significantly smaller than the average human hair.
The functionalized GQDs themselves are composed of nanocarbon materials containing a zwitterionic structure. These materials, in turn, comprise nanoparticles that contain an equal amount of both positive and negative charges yet still remain electronically neutral.
The nanoparticles, once added to the interface, separate the two fluids by making one side hydrophobic and the other side hydrophilic, researchers said. In addition to stabilizing the emulsion, the GQDs also served to control the molecular diffusion on the fluid-fluid interface by adjusting its pH values--a process akin to flipping a light switch.
The electronic components of the GQDs also allowed researchers to control the overall pH of the interface between the fluids and, in doing so, finetuning the GQDs to both block and unblock an oil-water interface.
“Usually, this is very difficult to do,” Wang observed in a press statement. “And sometimes, if we can control the release, but the system itself is not stable; it may only be possible to do one or two cycles of this before the system collapses.”
Moreover, changing the nanoplatelets on the interface to the same charge means that they disassemble, thus creating a more stable emulsion system.
The team published a paper on their work in the journal ACS Applied Materials & Interfaces.
The research has a number of applications, including helping design a high-performance fire-suppression system, Wang said. Emulsions are used to extinguish certain types of fires.
“In addition, because we can control the release, this could be promising for drug delivery and enhanced oil recovery,” Wang added.
Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time, she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.