Evidence for asymmetric edge-on Langmuir monolayer: Application to surface potential measurements

We show, using surface pressure vs. molecular area isotherm measurements and synchrotron grazing X-ray diffraction, that 4BCD12 molecules, which consist of a central flexible bowl-like core to which eight long lateral hydrocarbon chains are bound, form a stable edge-on monolayer. Experimental data indicate that six lateral hydrocarbon chains orient upwards to form a quasi-rectangular lattice of 43° tilted hydrocarbon chains. The obtained axially asymmetric phase, which we label edge26-on, allows using surface potential measurements, for the validation of literature electric models of a single monolayer spread at the air-water interface.