Simple technique yields complex structures
In a discovery with potential uses from electronics to biology, Princeton engineers have invented a simple procedure for making microscopically small particles assemble themselves into complex materials.
The technique allows scientists to force mixtures of tiny beads to crystallize into tailored structures that could be ideal for channeling laser light through next-generation telecommunications devices or for mechanically sorting DNA molecules as part of cheaper, faster biological tests.
In a paper published recently in Physical Review Letters, chemical engineering graduate student William Ristenpart and Professors Dudley Saville and Ilhan Aksay showed how they could start with a liquid suspension of jumbled silica and polymer particles and subject them to high frequency alternating currents to guide the particles into various structures.
The technique bypasses the expensive and painstaking lithographic techniques that are currently used to make minute structures. Lithography uses a highly energized beam of electrons to carve material one feature at a time. With Ristenpart's approach, the particles all assemble themselves into patterns in a matter of seconds.
A benefit of the discovery is that it lets scientists manipulate two kinds of particles at once -- glass and plastic -- and to control their behavior somewhat independently, even when the different particles are essentially the same size. Previous self-assembly efforts have focused on making structures out of a single kind of particle or out of particles of significantly different sizes. The new technique allows a richer variety of structures, because both the frequency of the electric field and the chemical properties of the particle ingredients can be adjusted.
"In a manner of speaking, you now have two knobs to turn," said Saville, who is Ristenpart's co-adviser and a co-author of the paper.
"It's very fast, practical and economically viable," said Aksay, also a co-adviser and co-author.
The finding exemplifies the high quality of Ristenpart's work, his advisers said. The University recently named Ristenpart a winner of the Porter Ogden Jacobus Fellowship, which is the highest honor awarded to graduate students. The fellowship provides full tuition and a stipend for the final year of study for one student from each division: humanities, social sciences, natural sciences and engineering.
The full story is available in a news release.