Minimising monolayer collapse on Langmuir troughs

The stability (area loss as a function of time) of dipalmitoylphosphatidylcholine (DPPC) at the air–water interface is an important property in the context of studying its behaviour as a major component of synthetic lung surfactant. However, some Langmuir troughs cannot support a stable monolayer of lung surfactant for long periods of time owing to adhesion between the surfactant and the materials that compose the trough. In this work, the stability has been measured as a function of surface pressure, Wilhelmy plate length and width, compression barrier material and the height of the water surface relative to the edge of the compression barriers on a Nima 601M Langmuir trough. Octadecanoic acid (stearic acid) and a non-amphiphilic porphyrin, 5,10,15,20-tetrakis(3,4-bis[ethylhexyloxy]phenyl)-porphyrinatozinc (Zn EHO) have also been investigated in order to identify the features of area loss which are surfactant material dependent and those which are affected by the properties of the trough itself. Stability of the highly amphiphilic monolayers was greatly improved when using Delrin barriers instead of PTFE barriers but had little effect on the porphyrin monolayers.