As will be reported in the Dec. 9 issue of Physical Review Letters (published online Nov. 21), scientists at the University of Illinois at Urbana-Champaign have studied the phase transition in a supported bilayer and discovered some fundamental properties that could affect the material's performance in various applications.
"Like water turning into ice, bilayers can exist in either a fluid phase or a solid (gel) phase, depending upon temperature," said Andrew Gewirth, a professor of chemistry. "Using a sensitive atomic force microscope, we studied how the microstructure of these bilayers changed during the transformation process."
First, the scientists supported a phospholipid bilayer on a piece of exceptionally smooth mica. Then they studied the properties of this bilayer as it changed phases from fluid to gel and back to fluid. Because touching the surface would destroy the delicate film, the researchers used a noncontact mode in which they oscillated the probe tip in close proximity to the surface, and measured the resulting change in amplitude.
"The atomic force microscope images showed that the fluid to gel phase transition produced substantial tearing of the bilayer, resulting in numerous big, foam-like defects," Gewirth said.
Because the mica substrate was molecularly smooth with no significant surface defects, the scientists concluded that the rips and tears were caused by an intrinsic property of the phase transition itself.
"The gel phase is more dense than the fluid phase," Gewirth said, "so the defects are likely caused by the change in density and, to a lesser extent, by therm
Contact: James E. Kloeppel
University of Illinois at Urbana-Champaign