Langmuir-Blodgett Deposition of a Ring-Shaped Molecule (Valinomycin)

Valinomycin, unlike most surfactants, is a ring-shaped molecule; its hydrophilic groups are evenly distributed around the ring. By the Langmuir-Blodgett (LB) technique, a single monolayer of valinomycin can be deposited on withdrawing a (hydrophilic) glass or mica substrate from the subphase, but the contact angle is not appreciably changed by the deposition of this flat molecule. The monolayer then peels off as the substrate is reintroduced into the water. However, if a thin film of silver is first evapoated on the substrate or three monolayers of lead stearate deposited on it, multiple layers of valinomycin can be built up. LB multilayers can also be deposited on poly (methyl methacrylate) (PMMA). Monitoring the actual (dynamic) contact angle during the process of deposition suggests that, for successful LB deposition, the contact angle must be greater than 90° on immersion and less than 90° on withdrawal. For valinomycin this sequence occurs only with substrates whose contact angles are hysteretic even in clean water.