Flexible membranes have been studied for a long time in biology, pharmacology and medicine since they represent the main structural element for the amazing architecture of the living cell. In addition, physicists and chemists have been fascinated by the unusual properties of these structures which are very anisotropic: They consist of bilayers of molecules and thus are very thin with a thickness of only 4 - 5 nanometers; their lateral extension, however, is much larger and can be tens of micrometers. Therefore, flexible membranes are able to bridge the gap between the nano- and the microworld.
So far, our understanding of these structures was based on two rather different theoretical approaches. On the one hand, the behavior of membranes on the micrometer scale is well understood in terms of smooth surfaces as described by differential geometry. In this way, one can explain the many different shapes and topologies as observed in the optical microscope. On the other hand, our view about the membranes on the nanometer scale comes from computer simulations in which one studies discrete molecular models with atomic resolution. However, these two approaches have remained rather distinct and unrelated.
Recently, researchers at the Max Planck Institute of Colloids and Interfaces
(Physical Review Letters 82, 4 January 1999) have made the first explicit
connection between these two different levels corresponding to the nano- and the
microworld, respectively . Using Molecular Dynamics simulations of rather large
membrane segments, they studied both the self-assembly process and the physical
properties of such bilayer membranes, compare Fig.1. On molecular scales, these
membranes are observed to be rather mobile and to have rough surfaces arising
from molecular protrusions, i.e., from the relative displacements of individual
molecules. On length scales, which are only somewhat larger than the membrane
thickness, however, the membranes are found to undergo smooth bend
Contact: Thomas Weikl