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This study reports on the electrochemical characterisation of dioleoyl phospatidylcholine (DOPC) bilayer structures on a negatively polarised mercury (Hg) electrode. The bilayers are stable on the Hg surface between −1.0 and −1.3 V applied potential. The experimental approaches were:- (i) rapid cyclic voltammetry (RCV) to “fingerprint” the bilayers, (ii) potential step experiments to record Zn 2+ reduction and, (iii) electrochemical impedance. The results show the following. Both the specific capacitance (5 μF cm −2 ) and the specific resistance of the bilayer are higher and lower respectively than that of a defect-free free standing DOPC bilayer. This indicates the presence of water and ions in the bilayer within an applied negative field. The bilayer's resistance to electrolyte movement decreases with increase in negative potential to a minimum at −1.3 V. The DOPC bilayer is less permeable to Zn 2+ ions compared to the DOPC monolayer coated electrode at applied negative potentials and its permeability to Zn 2+ increases with an increase in negative applied potential. The specific capacitance of the bilayer increases to about 7.5 μF cm −2 with increase in applied negative potential showing the increasing significance of water in the bilayer commensurate with its increased permeability to ions. Adsorption of SiO 2 nanoparticles on the bilayer surface causes a step negative potential shift in the anodic capacitance current bilayer reformation peak indicating an acceleration of the bilayer reformation process. [ABSTRACT FROM AUTHOR]

The present study investigates the effect of electrolyte ions on the occurrence of potential induced phase transitions at ca. -0.93 V and -0.99 V vs Ag/AgCl respectively of dioleoyl phosphatidylcholine (DOPC) monolayers on the mercury (Hg) surface. The interaction of both inorganic and organic electrolytes with DOPC was studied and it was shown that the alterations in the nature of the capacitance peaks representing the successive phase transitions depend on the ionic strength and the interfacial properties of the electrolyte ions. Higher ionic strength and cations with stronger binding affinity to DOPC give rise to steeper electric fields across the phospholipid layer shifting the apparent potential characterising capacitance peak-1 to more positive values. Conversely the anion, I − , which binds to DOPC, lessens the field gradient across the lipid and shifts the potential characterising capacitance peak-1 to more negative potentials. At more negative potentials to those characterising capacitance peak-1, electrolyte penetrates the DOPC. As a consequence a higher ionic strength and smaller hydrated cations with higher charge density enhance the screening of Hg, leading to stronger electric fields at the Hg surface. This effect shortens the onset and increases the rate dependence on the potential of the adsorption of bilayer patches to Hg by a nucleation and growth (N & G) process. [ABSTRACT FROM AUTHOR]