Finite-size effects in biomimetic smectic films

Thin stacks of lipid multibilayers supported on rigid silicon and mica substrates are found to exhibit finite-size effects. Using neutron diffraction we find that the repeat spacing [Formula presented] of stacks containing up to a few tens of bilayers depends on their thickness [Formula presented], with [Formula presented] increasing with decreasing [Formula presented]. Differences in [Formula presented] are larger in the low-temperature [Formula presented] phase consisting of rigid bilayers than in the high-temperature [Formula presented] phase where the bilayers are more flexible. Various scenarios that may be responsible for this counterintuitive observation are discussed.