Acid-base properties and zeta potentials of self-assembled monolayers obtained via in situ transformations

Jing Jong Shyue, Mark R. De Guire, Tsuyoshi Nakanishi, Yoshitake Masuda, Kunihito Koumoto, Chaim N. Sukenik

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130 Scopus citations

Abstract

Siloxane-anchored, self-assembled monolayers (SAMs) on single crystal Si were prepared with a variety of surface functional groups using a single commercially available surfactant (1-bromo-11-(trichlorosilyl)-undecane) followed by in situ transformations. Polar (thioacetate and thiol), nonpolar (methyl), acidic (sulfonic and carboxylic), basic (various amines), and ionic (alkylammonium) surface functionalities were prepared. For primary amine and sulfonate surfaces, the degree of surface charge as a function of pH was determined ex situ using X-ray photoelectron spectroscopy (XPS). Sulfonate SAMs exhibited much higher effective pK a (∼2) than dilute sulfonic acid (-5 to -6), and amine SAMs exhibited much lower pK a (∼3) than dilute organic amines (∼10). This is attributed to the stabilization of nonionized groups by adjacent ionized groups in the SAM. Zeta potentials of these SAMs as a function of pH were consistent with the XPS results and indicated that ionizable SAM surfaces can generate surface potentials much higher than those of nonionic SAMs (thioacetate, methyl) and typical oxide surfaces.

Original languageEnglish
Pages (from-to)8693-8698
Number of pages6
JournalLangmuir
Volume20
Issue number20
DOIs
StatePublished - 28 Sep 2004

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