Lehigh Engineering graduate students Megan Casey and Yi-Ling (Ivan) Liang received the Excellence in Polymer Science & Engineering award at the meeting of the Lehigh Valley section of the Society of Plastics Engineers (SPE)
in late October. Each student also gave a brief presentation about their research to SPE members present at the meeting.
When oil and water don’t mix
In her presentation, Casey, a chemical engineering Ph.D. candidate working in the Emulsion Polymers Institute, discusses miniemulsion technology. Ordinary emulsions are mixtures of two immiscible (cannot be blended) liquids, aided by a surfactant. The surfactant acts as a mediator to keep one liquid dispersed in the other, otherwise the liquids would quickly separate into layers. If the liquids are monomers and water, the monomer can be polymerized to form polymer latexes, used in products like water-based paints, coatings, and adhesives.
Megan Casey and Ivan Liang
The large capacity of water allows it to absorb much of the heat generated by polymerization reactions making it a common component of emulsions. However, the process is limited to monomers that have at least some solubility in water, because the monomer must be able to diffuse through the water to the reacting polymer particles.
"Miniemulsion polymerization offers a way of polymerizing monomers that cannot diffuse through water at all," says Casey. "This includes monomers produced from renewable resources like vegetable oils which are typically very insoluble in water." By making the monomer droplets very small—on the "nano" scale—polymerization can occur in the monomer droplets themselves, and no diffusion is required.
Miniemulsions also offer a way to make encapsulates, and this sort of technology can be used to improve paints and coatings. "For example, pigments are usually the expensive components in paint," says Casey. "If you can encapsulate pigments well, you reduce how much pigment you need in a paint formula to produce the same effect." Encapsulating pigments results in a more even distribution of the particles in the paint.
Some of the active ingredients in pharmaceutical products are also insoluble in water, making them impossible to inject intravenously. Miniemulsions allow the active ingredients to be dispersed in water. "By stabilizing the ingredients in water instead of an oil or solvent, you not only create a safer medicine, but one that can be injected," Casey says.
A tougher material
Liang, a Ph.D. candidate in the Center for Polymer Science and Engineering, has been studying the addition of toughening agents to improve the crack resistance of epoxy resins. Two types of particles are used as toughening agents in his work: soft rubber particles or rigid, nano-sized silica particles. Combining both species into an epoxy resin forms a hybrid nanocomposite that is tougher than that created by only one of either of the individual particles.
Epoxy resins are used in a variety of ways including as adhesives, as insulators in electrical components, in paints and coatings, and in carbon fiber reinforced plastics—the material used in ski poles.
The addition of nano-sized silica particles into a rubber toughened epoxy improves the performance of the resin. In reinforced plastics, it creates a tougher substance that does not fracture as easily. A major part of Liang’s research is learning to understand how the nanosilica particles work within the hybrid nanocomposites.
"No one really knew exactly how nanosilica worked in hybrid nanocomposites before our study," he says. "Understanding the toughening mechanisms in the hybrid nanocomposites helps engineers to predict the fracture behavior in a more accurate—and therefore more economic—way."
"This award inspires young researchers like me to devote more effort to exploring the opportunities in plastic related fields," says Liang. As to what else drives him in the lab, Liang says, "Professor Raymond Pearson. He has always given me valuable advice in my research, especially when I was struggling to interpret experimental results that appeared to contradict each other. He encourages me to study problems from multiple points of view, and to seek the most efficient direction in my research."
"It makes me happy to think that this award means that I am contributing—at least in a small way—to the field of emulsion polymerization," says Casey. "I find miniemulsions particularly interesting because they can be used in such a wide range of applications. I am grateful to my advisors, Dr. Mohamed El-Aasser for his vision in this project, and Dr. Dave Sudol for being available every day to help and guide me through it. Dr. Sudol always tells me to question everything. Even if the technique has been performed a certain way for years, I should question it anyway. I think that is one of the best pieces of advice you can give to someone who wants to be a scientist."
The Excellence in Polymer Science and Engineering Award is sponsored by the Lehigh Valley Society for Plastics Engineering. Both Casey and Liang will have the chance to present their work again at the annual SPE meeting.