SPONTANEOUS CHIRAL-SYMMETRY BREAKING BY ACHIRAL MOLECULES IN A LANGMUIR-BLODGETT-FILM

THE spontaneous breaking of symmetry is responsible for many physical phenomena, including the mass differences of elementary particles and phase transitions in condensed-matter systems. The breaking of mirror symmetry leads to chirality. In general, chiral effects in condensed-m atter systems, such as optical activity, are associated with chiral mo lecular structures. But several recent observations1-3 of domain forma tion in thin organic films of achiral molecules have suggested that sp ontaneous separation into regions of differing chirality may occur in these systems. Eckhardt et al.4, meanwhile, have reported the spontane ous resolution of chiral molecules in Langmuir-Blodgett (LB) films. He re we present images of LB films of calcium arachidate obtained with t he atomic force microscope5, which suggest that these achiral molecule s can separate spontaneously into lattices with chiral packing of oppo site handedness. We suggest that this symmetry breaking is driven by t he interplay between the packing constraints imposed by the alkane tai ls and the molecular-area requirements set by the calcium ions6-13.