Interactions determining phospholipid domain growth in monolayers: experimental results and computer simulations, Suzanne Amador, Madison Compton, Lyle Roelofs, Nicholas Wilder, Physics Department, Haverford College, Haverford PA 19041.

Results are presented from a quantitative analysis of liquid condensed (LC) domain shapes in monolayers of the phospholipid dipalmitoylphosphatidylcholine (DPPC). Comparison with existing theory shows that the dominant dependence of LC domain shape factor on in-plane density is described well by electric dipole-dipole interactions; however, the detailed chirality of the LC domains remains unexplained. Also unaccounted for is the noncompact growth of LC domains either at electrolyte concentrations high enough to screen out electric dipole interactions, or in mixtures with anionic phospholipids. We have performed Monte Carlo simulations of domain growth using an Eden model with energetic contributions from line tension, dipole-dipole interactions, and a novel short-range chiral interaction term. We present results for the way in which these chiral interactions influence the geometry of the growing domains, yielding, e.g., noncompact domain growth even in the absence of dipole-dipole interactions.