Liang Xu, a chemical engineering Ph.D. student with the University of Houston Cullen College of Engineering, took first place in the poster presentation competition at a recent materials-research symposium.
The symposium, Frontiers in Materials Research: Applications of Thermal Analysis and Rheology, was held on April 20 in Dallas. It was hosted by The Texas and Southwest Thermal Analysis and Rheology Forum.
During the symposium, Xu presented his poster “Manipulation of Structures of Block Copolymers with Layered Silicates,” based on research conducted under the direction of Ramanan Krishnamoorti, professor of chemical engineering and the college’s associate dean for research.
The poster outlines Xu’s research into layered silicate nanofillers that are used to strengthen block copolymers.
Block copolymers are nanometer-scale objects that have multiple applications, ranging from semiconductors to fuel cells. One of their drawbacks is that they are easily damaged. Researchers have found, however, that they can withstand more punishment if they are mixed with nanoparticle fillers, such as layered silicates, that absorb the stress of impacts.
When layered silicates are created, though, they are bound together in stacks, one on top of another. These stacks prevent the silicates from being dispersed effectively throughout the block copolymers. It is necessary, then, to force these stacks apart. Xu is accomplishing this through in situ stable free radical polymerization.
With this approach, stacks of layered silicates are exposed to monomers. Researchers then use an initiator chemical, which is initially attached to the silicate surface, to cause these monomers to bond, thereby forming polymers.
“As the polymer chains grow, they push the stacks of layered silicates apart, dispersing them. The polymer chains also keep these layers from coming back together,” said Liang.
Once dispersed throughout a block copolymer matrix, these layered silicates serve to strengthen the block copolymers, while at the same time making them easier to use in various applications.
This is because block copolymers self-assemble into groups when in the melt (a soft, non-solid, non-liquid state) they reside in is lowered below a specific temperature. This self-assembly is imperfect, however, since the block copolymers are orient themselves in different directions, making them difficult to use.
The addition of layered silicate nanofillers solves this problem. If they are added to the block copolymer in the melt state, the bock copolymers will organize themselves in around the layered silicates as the melt’s temperature is lowered past the self-assembly point, giving them a uniform orientation, hence making them easier to apply
“The nanoparticles serve as directing agents,” said Xu. “They direct the diblock copolymers to form an outer structure in the same direction.”
By providing direction and strength to block copolymers, Xu’s research could help scientists overcome two of their primary flaws. As a result, this niche of nanotechnology could be brought one step closer to impacting everyday life.