Supporting Information

Size: px

Start display at page:

Download "Supporting Information"

George Cobb
5 years ago
Views:

1 Redox-Induced Ion Pairing of Anionic Surfactants with Ferrocene-Terminated Self-Assembled Monolayers: Faradaic Electrochemistry and Surfactant Aggregation at the Monolayer/Liquid Interface Eric R. Dionne, Tania Sultana, Lana L. Norman, Violeta Toader, and Antonella Badia Supporting Information S 1

2 8 (A) / mv s E / V (vs. Ag/AgCl) 1 (B) r = Peaks I Peaks II r = / mv s -1 Figure S1. FcC 1 SAu SAM in.1 M NaClO 4 /.1 M HClO 4(aq). (A) CVs as a function of the scan rate. The arrows indicate the direction of potential cycling. (B) Anodic peak current i as a function of the scan rate. Peak I signifies the anodic peak at lower potential while Peak II is the peak at higher potential. The peak current data points represent the average value and standard deviation of experiments carried out on three different FcC 1 SAu SAMs. S

3 Baseline-corrected Data Gaussian-Lorentzian Fit Gaussian Fit Lorentzian Fit Baseline 3% 7% E / V (vs. Ag/AgCl) Figure S. Example of the mathematical deconvolution of the anodic segment of a CV recorded for the FcC 1 SAu SAM in.1 M NaClO 4 /.1 M HClO 4(aq) at a scan rate of 1 mv s -1. S 3

4 E / V (vs. Ag/AgCl) Figure S3. Electrochemical stability of FcC 1 SAu SAM in 33 mm NaC 1 SO 4(aq). Six successive CVs run at a scan rate of 1 mvs -1. The arrows indicate the direction of potential cycling. The CMC of NaC 1 SO 4 in water is 33. mm. S 4

5 (A) (B) E / V vs Ag/AgCl E / V vs Ag/AgCl (C) Q Fc + / C cm (D) E / V vs Ag/AgCl E / V vs. Ag/AgCl Figure S4-1. FcC 1 SAu SAM in 1 mm NaC 1 SO 4(aq). (A) CV (scan rate = 1 mv s -1 ). (B) Baseline determination (red line) of the anodic segment of the CV in (A) using Microcal Origin software. (C) Anodic segment corrected for the charging current using the baseline shown in (B). (D) Plot of the ferrocenium charge density as a function of the applied potential generated by numerical integration of the curve in (C). The total ferrocenium density is 7.9 μc cm -. S 5

6 (A) 3 (B) E / V vs. Ag/AgCl E / V vs. Ag/AgCl 3 1 (C) Q Fc + / C cm (D) E / V vs. Ag/AgCl E / V vs. Ag/AgCl Figure S4-. FcC 1 SAu SAM in 13 mm NaC 8 SO 4(aq). (A) CV (scan rate = 1 mv s -1 ). (B) Baseline determination (red line) of the anodic segment of the CV in (A) using Microcal Origin software. (C) Anodic segment corrected for the charging current using the baseline shown in (B). (D) Plot of the ferrocenium charge density as a function of the applied potential generated by numerical integration of the curve in (C). The total ferrocenium density is 4.7 μc cm -. S 6

7 Q / C cm Q Fc + = 8.5 C cm E / V vs. Ag/AgCl Figure S5. Chronocoulometry measurement of the ferrocenium charge density generated by the oxidation of a FcC 1 SAu SAM in 1 mm NaC 1 SO 4(aq). Plot of the charge densities obtained by successive double potential step chronocoulometry experiments. The initial potential (E initial ) was set at 53 mv (ca. 15 mv positive of E ) and held for 1 seconds, which should be long enough for all of the oxidizable ferrocenes to be oxidized. The potential was then stepped in increments of 1 mv from E initial to more negative potentials (E variable ) and E variable was held for 1 second to achieve the fraction of reduction dictated by the Nernst eq. The system was stepped back to E initial, and the resulting current transient measured for 1 s. The quantity of charge ( Q) generated between E initial and E variable ( E) was determined using an Anson plot. The total charge is the sum of the charges associated with capacitive (charging) and Faradaic processes. At potentials < 15 mv (charging process), Q varies linearly with potential with a constant slope (red line), allowing the Q value at 53 mv to be accurately corrected for charging/capacitive contributions to give Q Fc +. S 7

8 E o' / mv 55 1/4 CMC 1/ CMC 5 1 CMC CMC C n Figure S6. Dependence of the measured FcC 1 SAu SAM redox potential E on the n- alkyl chain length C n of the surfactant anion, where C n is the number of carbons, given for different sodium alkyl sulfate concentrations expressed in multiples of the CMC. The average slope of the linear regressions is -±3 mv C -1 n. The data points for each surfactant concentration were fit with a fixed slope of - mv C -1 n, giving r = (1/4 CMC), r = (1/ CMC), r = (CMC), and r = ( CMC). The E data points represent the average value and standard deviation of experiments carried out on at least three different FcC 1 SAu SAMs. S 8

9 3 1 M to 1 mm NaClO 4 5 Peak I Peak II 1-1 E o' / mv (A) E / V (vs. Ag/AgCl) 3 (B) log ([NaClO 4 ] / M) log (a ClO4 - / M) :1 Correlation (C) log ([NaClO 4 ] / M) Figure S7. (A) CVs (scan rate of 1 mvs -1 ) recorded for a FcC 1 SAu SAM as a function of the NaClO 4 concentration, from 1. mm to 1. M. (B) Measured FcC 1 SAu SAM redox potential E plotted as a function of the logarithm of the NaClO 4 molar concentration. The data was fit to a linear function with a fixed slope of -59 mv. r = (peak I) and r = (peak II). The data points represent the average value and - standard deviation of three different experiments. (C) Plot of the logarithm of the ClO 4 activity versus the logarithm of the molar concentration of NaClO 4. The ClO - 4 activity coefficients were calculated from the Davies equation for solution ionic strengths from.1 M to.5 M. S 9

10 E o' SAM rel. / mv /4 CMC 1/ CMC 1 CMC CMC C n Figure S8. Relative apparent redox potential Eo SAM rel. as a function of n-alkyl chain length C n of the surfactant anion shown for different sodium alkyl sulfate concentrations expressed in multiples of the CMC. The average slope of the independent linear regressions is -9±1 mv C n -1. The data points for each surfactant concentration were fitted with a fixed slope of -9 mv C n -1, giving r = (1/4 CMC), r = (1/ CMC), r = (CMC), and r = -1 ( CMC). S 1

11 175 E fwhm / mv (A) Peak I Peak II log([naclo 4 ] / M) E p / mv (B) Peak I Peak II log([naclo 4 ] / M) Figure S9. Data from the CVs of FcC 1 SAu SAMs recorded in NaClO 4 /HClO 4 as a function of the NaClO 4 concentration. (A) Formal widths at half-maximum ΔE fwhm of the anodic peak and (B) anodic-to-cathodic peak separation ΔE p versus the logarithm of the NaClO 4 concentration. The data points represent the average and standard deviation of three different FcC 1 SAu SAMs. S 11

12 Table S1. Adsorbed dodecyl sulfate layer thicknesses and surface concentrations reported in the literature for different interfaces. System Ref Technique d / nm / mol cm - Adsorbed layer morphology Gibbs monolayer (air/ aqueous Na 1 SO 4 solution interface) 1, Surface tension N/A (excess added salt) uniform monolayer polystyrene film 3 NR (±.) 1-1 N/A C 11 S/Au SAM 4 SPR (±.) 1-1 hemicylindrical surface micelles C 11 S/Au SAM 5 SPR (±.1) 1-1 hemicylindrical surface micelles C 11 S/Au SAM 5 NR N/A hemicylindrical surface micelles electrified Au(111) 6 NR metal -E 1.3 (-3 mv vs SCE) 1.37 (+1 mv vs. SCE) hemicylindrical surface micelles NR = neutron reflectivity, SPR = surface plasmon resonance, metal -E = charge density vs. electrode potential S 1

13 References 1. Sasaki, T.; Hattori, M.; Sasaki, J.; Nukina, K. Bull. Chem. Soc. Jpn. 1975, 48, Tajima, K. Bull. Chem. Soc. Jpn. 1971, 44, Turner, S. F.; Clarke, S. M.; Rennie, A. R.; Thirtle, P. N.; Cooke, D. J.; Li, Z. X.; Thomas, R. K. Langmuir 1999, 15, Levchenko, A. A.; Argo, B. P.; Vidu, R.; Talroze, R. V.; Stroeve, P. Langmuir, 18, Martinez, J.; Talroze, R.; Watkins, E.; Majewski, J. P.; Stroeve, P. J. Phys. Chem. C 7, 111, Burgess, I.; Zamlynny, V.; Szymanski, G.; Lipkowski, J.; Majewski, J.; Smith, G.; Satija, S.; Ivkov, R. Langmuir 1, 17, S 13

Fundamental molecular electrochemistry - potential sweep voltammetry

Fundamental molecular electrochemistry - potential sweep voltammetry Potential (aka voltammetric) sweep methods are the most common electrochemical methods in use by chemists today They provide an efficient