Factors governing the reversible change in ionic permeability of a low-density monolayer

摘要: Abstract The dynamic response of low-density self-assembled monolayers (SAMs) on gold has been investigated with electrochemical impedance spectroscopy (EIS) under non-faradaic conditions and contact angle measurements. 16-mercaptohexadecanoic acid (LD-MHA) SAMs is compared that densely-packed MHA tetraethylammonium–MHA (TEA–MHA) ion-pair in 0.1 M KCl (pH 8.4). films composed ion-pairs loosely-packed have higher capacitance are more permeable to ions than fully-packed SAMs. phase the LD-MHA SAM at 0.1 Hz decreases reversibly by 10° upon scanning applied potential from −0.1 V +0.3 V (vs. SCE). Fitting data an equivalent circuit correlates decrease order-of-magnitude drop monolayer resistance (i.e. increase ionic permeability monolayer). dense do not exhibit capacitances TEA–MHA a small, but significant (15%), change between found be independent electrolyte concentration (0.01–1 M KCl), displays hysteresis direction scan. Receding measurements performed using same show caused voltage-induced structural (molecular re-organization) within film. agreement EIS pH 3.3 8.4 shows electrostatic attraction negatively-charged thiol tailgroup oppositely-charged electrode required for this occur.