Monolayer collapse behavior of dipalmitoyl phosphatidylcholine with normal long-chain alcohols at the air/water interface

This study investigated the collapse behavior of mixed dipalmitoyl phosphatidylcholine (DPPC)/normal long-chain alcohol monolayers at the air/ water interface at 37°C. Surface pressure variations with time for the mixed monolayers of DPPC with 20 mol% n-hexadecanol, n-octadecanol, and n-eicosanol at corresponding collapse points were recorded by a Langmuir trough system. Furthermore, the collapse monolayers at various relaxation times were transferred to glass substrates for fluorescence microscopy (FM) observations by the Langmuir-Blodgett deposition technique. From the analysis of surface pressure relaxation data, it was found that the data could be fitted by a two-stage nucleation and growth model with the Prout-Tompkins and the second order kinetic equations. The addition of normal long-chain alcohols in a DPPC monolayer resulted in higher rate constants for the monolayer relaxation processes with the extent increasing with hydrocarbon chain length of the alcohols. The FM images demonstrated that pronounced domain formation was associated with a longer relaxation time for the collapse DPPC and DPPC/alcohol monolayers, and the presence of normal long-chain alcohols appeared to enhance the relaxation processes. Moreover, the formation of extraordinary stripe structures during the collapse process of a mixed DPPC/alcohol monolayer became significant with increasing hydrocarbon chain length of the alcohols.