Bubblepack on a Nanoscale

Scientists have found a way to make a kind of bubblepack--similar to the stuff in which you wrap fragile objects for shipment--with chambers small enough to crowd even a single virus. The finding, reported in the 12 February issue of Science, may help scientists to sort molecules or study the physical characteristics of materials.
     The finding was triggered by the search for a new way to sort optical isomers, organic molecules that come in two different versions, one the mirror image of the other. Because these often react differently, they have to be separated and tested individually before they can be used as drugs or pesticides. Thomas Mallouk, a materials chemist at Pennsylvania State University, University Park, wanted to devise a new way to do this by sending a stream of mixed isomers through a material honeycombed with tiny pores that he would load with chemicals that bind one version of the isomer. Because a three-dimensional organic material with the right pore size (10 to 100 nanometers) to hold the isomer and the chemical binder didn't exist, Mallouk and his students Stacy Johnson and Patricia Ollivier set out to invent one.
     The team made millions of 35-nanometer balls out of silica, the building block of quartz, filled them into a press, and heated them to 800 degrees Celsius, just enough to fuse the balls together where they touched. Over this lattice-work of fused balls they poured a solution of divinylbenzene, a molecule that easily forms long chains called polymers. After the polymerization of divinylbenzene was complete, they dissolved away the core of silica balls. The result: a dime-sized piece of a Swiss cheese-like polymer, with all the pores exactly the same size and interconnected. The team also discovered they could set the final pore size of the lattice between 15 and 35 nanometers by using a mixture of two monomers: one that shrinks when processed into a polymer and one that stays rigid. The more shrinkable monomer they used, the smaller the final pore size.
     The nanobubblepack can be inexpensively made by the kilo, says Mallouk, who is currently exploring its usefulness in isomer separation. But there may be other applications. The material could be used to make tiny spheres in different sizes of interesting materials, which physicists could use to systematically study how magnetic, optical, or thermo-electric properties change as the size of a particle gets smaller and smaller. David O'Brien, a biopolymer chemist at the University of Arizona in Tucson, says changing the monomer mixture to vary the bubblepack's pore size is "a very attractive concept."
     --Liese Greensfelder

Definitions from the AP Dictionary of Science and Technology

Related Pages on APNet

• Journal of Colloid and Interface Science
• Journal of Catalysis
• Journal of Solid State Chemistry

Related links from the article above:

• Thomas E. Mallouk
• University of Arizona Department of Chemistry
• Particle Physics in the UK
• Foresight Institute
• Nanotechnology
• Sean Morgan's Nanotechnology Pages
• Polymer Chemistry Hypertext

© 1999 The American Association for the Advancement of Science
This item is supplied by the AAAS Science News Service