Electrochemically directed two-component monolayers on gold
- PDF / 130,785 Bytes
- 6 Pages / 584.957 x 782.986 pts Page_size
- 102 Downloads / 197 Views
Self-assembled monolayers (SAMs) were formed on gold at anodic potentials from solutions containing two different alkyl thiosulfates, CH3(CH2)10S2O3Na and HO2C(CH2)10S2O3Na. The resulting two-component SAMs were analyzed using x-ray photoelectron spectroscopy to relate their compositions to those of the solutions from which they were adsorbed. This relationship was more linear than reported for analogous SAMs adsorbed from mixed solutions of alkanethiols. The wettability of these surfaces by water and by hexadecane was also measured and compared to analogous SAMs prepared by chemisorption of thiols from solution.
I. INTRODUCTION
Developing the ability to control surface composition in a way that approaches the ease with which solutions can be prepared remains an important goal of surface and interface science. A convenient approach to controlling interfacial structure is the spontaneous chemisorption of alkanethiols (or dialkyl disulfides) to form self-assembled monolayers (SAMs) on gold.1 Adsorption of SAMs from solutions containing a mixture of thiols with different tail groups provides an added degree of flexibility in the preparation of more complex surfaces. Such systems with equivalent chain lengths have been systematically studied and are often characterized by a nonlinear relationship between the composition of the SAMs and that of the solutions from which they were adsorbed.2–10 Competitive adsorption/equilibration from mixtures of thiols having different chain lengths have also been reported.5,9–30 We have developed an alternative approach to the formation of SAMs, which allows spatial control of where the monolayer forms: electrochemically directed chemisorption from solutions of alkyl thiosulfates on gold electrodes at anodic potential.31,32 These monolayers can be formed by applying a series of square-wave potentiometric pulses to a gold electrode in a solution of the alkyl thiosulfate(s) of interest and tetra-n-butyl ammonium tetrafluoroborate as a supporting electrolyte, in tetrahydrofuran (THF). We recently reported that a range of terminal functional groups (X(CH2)nS2O3Na; X 5 CH3, (CF2)8CF3, CO2H, CO2CH3, CONH2) are compatible with this method, thus allowing the current study of twocomponent SAMs.33 The primary objective of this study was to examine the relationship between the composition of SAMs adsorbed a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2010.13 262
J. Mater. Res., Vol. 26, No. 2, Jan 28, 2011
http://journals.cambridge.org
Downloaded: 18 Mar 2015
from mixtures of two alkyl thiosulfates and the solutions from which they were adsorbed. The alkyl-thiosulfate precursors, CH3(CH2)10S2O3Na and HO2C(CH2)10S2O3Na, were selected so that these systems could be compared with those previously reported for SAMs adsorbed from solutions of the analogous alkanethiols, CH3(CH2)10SH and HO2C(CH2)10SH. Such benchmarking of the electrochemical method can provide fundamental insight into similarities and differences in the two types of adsorption process, as w
Data Loading...
