join these two
In the fall of 1878, Randolph McCoy accused Floyd Hatfield of stealing a hog, sparking a long-running family feud now famous in American lore. If crammed in a room, the men and their families probably would have stared at each other from distant corners, but had they all been made of plastic, a technique developed by a team of UCSB researchers might allow the clans to happily intermingle and possibly even hold hands.
The advantage of the process, published last month in the journal “Science,” is that it allows engineers to create materials that exhibit the characteristics of expensive, designer plastics like polyaniline – which conducts electricity – while using only a small amount of it amidst a sea of inexpensive, ordinary plastics like Styrofoam.
“This allows you to exploit the special properties of a minority component while the majority component fills up space,” said one of the paper’s lead authors, UCSB professor Glenn Fredrickson
“Imagine freezing beer foam and cutting through it,” he said. “The honeycomb-like structure you would see is like the solid plastic structure we have produced,” where the air bubbles would be analogous to the Styrofoam, and the beer between the bubbles would be analogous to the specialty material.
According to Fredrickson, it was the first time scientists had produced a structure where two plastics were evenly distributed throughout a solid object. Before, any two would tend to separate out much like oil and water, and since the specialty plastic wasn’t continuous throughout the final product, its properties weren’t useable.
A major application of the resulting material would be in the semiconducting industry, where engineers could use the material written about in “Science” to coat objects to enable them to conduct electricity, but there are also more mundane applications, like in the production of food containers.
Certain plastics let certain gasses pass through, and none are completely airtight; ketchup bottles, for example, need a special plastic laminate on the inside that acts as an oxygen barrier to prevent the condiment from spoiling, but the drawbacks are that the laminate is expensive to apply and it prevents the bottle from being recycled
In theory, scientists could use the UCSB technique to manufacture inexpensive oxygen-proof paint, exhibiting the properties of a specific oxygen-proof plastic, in which to dip the ketchup bottles. This could require so little of the expensive plastic that the bottles may still be recyclable and would be more economical to produce.
Fredrickson also explained that researchers could manufacture UV-proof films to apply to windows, vapor barriers for plastic beer bottles, paints for use in silicon chip manufacturing, or – with the help of a conductive designer plastic such as polyaniline – make a thin film or paint that would conduct electricity. All these products would use far less of the expensive plastic because the bulk of the product would be made from cheap plastic while the properties that make them useful would come from the designer one.
The road to creating their film would have been a lot easier if the researchers could have simply mixed designer plastics with the Styrofoam, but this didn’t work since the materials have a molecular repulsion away from each other. Combining them would have been akin to asking the Hatfields and the McCoys to kiss and make up.
“Think of it in terms of oil and water,” said UCSB’s Edward Kramer, one of the paper’s co-authors. “If you have a water surface and you stick a drop of oil on top of it, it’ll bead up.”
Instead, the scientists had to develop a way to essentially dress up the Hatfields so that the McCoys would take a liking to them. The disguise they came up with, which is known as a block copolymer, served as their costume. Once they attached the designer plastic to the block copolymer (the costume), the scientists could, in a solvent, introduce the designer plastic to the bulk plastic and not have the two materials repel each other.
Back to the oil and water analogy: “If you put a layer of soap on the water surface and then put the oil on the water, the oil will spread out,” said Kramer. “Essentially the role of the block copolymer was similar to the role of the soap – it kept the (designer plastic) polyaniline from beading up.”
Then the scientists were able to get one end of the block copolymer to bond with Styrofoam, while the aniline – attached to the other end of the block copolymer – stuck out into space. As the solvent evaporated away, the researchers noted that the expensive plastic didn’t bead up – instead its strands intertwined. The end result was a sort of honeycomb pattern consisting of relatively large balls of cheap Styrofoam surrounded by a very thin layer of aniline.
While the technique holds promise in material design, Fredrickson acknowledged that it is still “far from commercialization. This is just the demonstration of a concept and we still need to find out exactly where the financial benefit is.”