An indirect laser-induced temperature jump determination of the surface pK{sub a} of 11-mercaptoundecanoic acid monolayers self-assembled on gold

Journal Article · Thu Mar 11 04:00:00 EST 1999 · Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical

DOI:https://doi.org/10.1021/jp983325z· OSTI ID:335245

Smalley, J F; Chalfant, K; Feldberg, S W ^[1]; Nahir, T M; Bowden, E F ^[2]

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1. Brookhaven National Lab., Upton, NY (United States). Dept. of Applied Science
2. North Carolina State Univ., Raleigh, NC (United States). Dept. of Chemistry

The indirect laser-induced temperature jump (ILIT) method is used to determine the acidity (pK{sub a}) of monolayers composed of 1-mercaptoundecanoic acid (MUA) self-assembled on vapor-deposited gold film electrodes in contact with either 0.10 or 1.0 M ionic strength NaClO{sub 4} electrolyte solutions. The ILIT technique may be used to measure the pK{sub a} of a surface-attached acid because the magnitude of the ILIT response is related to the potential gradient at the electrode/electrolyte interface which is, in turn, related to the extent of ionization of the acid. The relevant data are the potentials of zero ILIT response versus pH. A simple two-layer model of the acid-modified electrode/electrolyte interface and Gouy-Chapman double layer theory (modified for the onset of dielectric saturation effected by the large concentration of charge present at this interface when a substantial fraction of the carboxylic acid moieties are ionized) were employed to analyze these data. This analysis gives pK{sub a} = 5.7 {+-} 0.2 at 0.10 M ionic strength and pK{sub a} = 4.4 {+-} 0.2 at 1.0 M ionic strength while the total concentration of MUA comprising the self-assembled monolayer is determined to be essentially the same at both ionic strengths, averaging (5.4 {+-} 0.3) {times} 10{sup {minus}10} mol/cm{sup 2}. Reasons for the observed variation of pK{sub a} with ionic strength are discussed.

• Sponsoring Organization: USDOE, Washington, DC (United States)
• OSTI ID: 335245
• Journal Information: Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Journal Name: Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical Journal Issue: 10 Vol. 103; ISSN 1089-5647; ISSN JPCBFK
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
ELECTROLYTES
GOLD
INTERFACES
LASERS
PH VALUE
TEMPERATURE DEPENDENCE
THIN FILMS
THIOIC ACIDS