Sandia LabNews

Labs researchers honored by C&E News

Researchers cited for two of top nine developments in 2002

Researchers cited for two of top nine developments in 2002

In an emphatic recognition of Sandia’s research, the Dec. 16 Chemical and Engineering News (C&E News) — the widely distributed weekly publication of the American Chemical Society — designated two Labs developments among the nine most interesting materials achievements of 2002.

Ann Mattson and Dwight Jennison (both 1114) were cited for providing a method to mathematically calculate adhesion energies that successfully matched experimentally measured values. Remarkably, the match holds true regardless of the particular density function used for the computation. The method offers scientists what may be the first firm handle on computing bond strengths and adhesion energies at interfaces.

Says Dwight, "I’m pleasantly shocked that C&E News would pick a theoretical advance to be among the top material achievements of the year."

"The theoretical success promises, at least, some understanding of the elusive bonding mechanism at such interfaces," said Charles Campbell, professor of chemistry at the University of Washington at Seattle and the editor of the journal Surface Science.

The finding was the subject of the first Perspective — a kind of gloss — ever published by Surface Science, says Dwight. "Our work was highlighted because it is a general method to compute the surface energies of all materials. These energy values are needed not just for the computation of adhesion — where two surfaces disappear — but also to understand the general properties of crystal shapes, which depend to some extent upon surface energies."

The bonding of thin films to metal — often oxides of metal to the metal itself — is crucial to numerous applications in joining, microelectronics, and catalysis. The Sandia researchers used corrected mathematical forms of a metal and metal oxide’s surface energy æ a property that governs wetting and adhesion between dissimilar materials. The advance by Ann and Dwight builds upon work by Ann and chemistry Nobel laureate Walter Kohn.

Meanwhile, Sandia researcher Joe Cesarano (1843) teamed with Professor Jennifer Lewis of the University of Illinois at Urbana-Champaign in using colloidal gels (inks) and solid freeform fabrication to automatically construct intricate 3-D structures with micrometer-size features and overall dimensions of a few millimeters.

For a visual image of the importance of the technique, C&E News wrote, "Imagine building a staircase using only one tool: a spray gun that squirts out a stream of concrete that spontaneously assumes the required shape."

Possible uses include advanced ceramics, photonic materials, catalyst supports, and bio-compatible tissue scaffolds.

The approach is based on robocasting — a process developed by Joe, in which a computer-controlled robotic arm delivers material through a fine nozzle onto a moving platform to build structures one layer at a time.

Joe and Lewis, working with John Stuecker (1843) and graduate student James Smay (now an assistant professor of chemical engineering at Oklahoma State University), used polyelectrolytes to carefully control the forces acting between colloid particles and to optimize the rheology of the gels for building self-supporting three-dimensional meshes of rods. These structures have been demonstrated for several different structural, catalytic, and electronic ceramic materials and were highlighted on the cover of the journal Langmuir.