New approach for measuring lateral diffusion in Langmuir monolayers by scanning electrochemical microscopy (SECM): Theory and application

Citation
J. Zhang et al., New approach for measuring lateral diffusion in Langmuir monolayers by scanning electrochemical microscopy (SECM): Theory and application, J PHYS CH B, 105(45), 2001, pp. 11120-11130
Citations number
82
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF PHYSICAL CHEMISTRY B
ISSN journal
1520-6106 → ACNP
Volume
105
Issue
45
Year of publication
2001
Pages
11120 - 11130
Database
ISI
SICI code
1520-6106(20011115)105:45<11120:NAFMLD>2.0.ZU;2-I
Abstract
A new SECM approach for studying the lateral diffusion of redox-active amph iphiles in Langmuir monolayers at an air/water (A/W) interface is described . To apply this technique practically, a triple potential step transient me asurement is utilized at a submarine ultramicroelectrode (UME) placed in th e water phase close (1-2 mum) to the monolayer. In the first potential step , an electroactive species is generated at the UME by diffusion-controlled electrolysis of a precursor. This species diffuses to, and reacts with, the redox-active amphiphile at the A/W interface resulting in the formation of the initial solution precursor, which undergoes diffusional feedback to th e UME. In this first step, the rate constant for electron transfer between the solution mediator and the surface-confined species can be measured from the UME current-time transient. In the second period, the potential step i s reversed to convert the electrogenerated species to its initial form. Lat eral diffusion of electroactive amphiphile into the interfacial zone probed by the UME occurs simultaneously in this recovery period. In the third ste p, the potential is jumped in the same direction as for the first step and the corresponding UME current-time transient can be used to determine eithe r the distance between the UME tip and the monolayer at the water surface, or the lateral diffusion coefficient of the amphiphile. A theoretical treat ment for this technique is developed and discussed in detail. The method is demonstrated experimentally with measurements of the lateral diffusion of N-octadecylferrocenecarboxamide in a 1:1 Langmuir monolayer with 1-octadeca nol.