Acid−Base Properties and Zeta Potentials of Self-Assembled Monolayers Obtained via in Situ Transformations

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 pKa (approximately 2) than dilute sulfonic acid (-5 to -6), and amine SAMs exhibited much lower pKa (approximately 3) than dilute organic amines (approximately 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.

Patterning of Silica Particles Using Self-Assembly on Two-Dimensional Patterns Fabricated from Phase-Separated Langmuir-Blodgett Films

“…Above results are explained by considering mainly the local zeta potential of functionalized and unfunctionalized templates and in one case the interfacial tension of the templates [19,20]. Figure 4 shows the schematic illustrations of the formation of self-assembled arrays of silica particles under the various conditions investigated above.…”

Template-controlled mineralization: Determining film granularity and structure by surface functionality patterns

“…The zeta potential of the amino-functionalized SAM is charged slightly positive during the reaction [28,29] due to protonation of the amino groups (-NH 3 + ) at this pH. Additionally, a Stern layer is present, which is formed by negatively charged counter ions [29,30].…”

“…Additionally, a Stern layer is present, which is formed by negatively charged counter ions [29,30]. The particles in solution can interact with these anions and Coulomb forces lead to a strong binding to the surface (Figure 2).…”

Fabrication and BSA Adsorption/Desorption Properties of Titania/Silica Composite Films Modified with Silane Coupling Agents

“…The pH value of the BSA dispersion is 7. Amino groups of the composite films are positively charged at around pH 7 37 . BSA is negatively charged in the dispersion owing to the dissociation of carboxylic groups.…”