Authors Chan, Y.-H. M. ; Schweiß, R. ; Werner, C. ; Grunze, M.
Title Electrokinetic Characterization of Oligo- and (Polyethylene Glycol)- Terminated Self-Assembled Monolayers on Gold and Glass Surfaces
Date 12.09.2003
Number 11677
Abstract Force-distance studies suggest that electrostatic forces play a dominant role in the resistance of oligo(ethylene glycol) (OEG) terminated self-assembled monolayers (SAMs) to adsorption from aqueous solution,whereas for end grafted poly(ethylene glycol) (PEG) coated surfaces inertness is explained by a stericrepulsion effect. To study the role of electrostatics in the repulsive forces measured on methoxytri(ethyleneglycol) (EG<SUB>3</SUB>OMe) terminated alkanethiolate SAMs on gold surfaces, their electrokinetic potentials andcharging properties were determined with the microslit electrokinetic setup (MES) using rectangularmicrochannels formed by SAM-covered sample carriers. The zeta potentials measured on the (EG<SUB>3</SUB>OMe)SAMs, both on gold and on glass substrate, indicate preferential hydroxide ion adsorption from the aqueousphase resulting in a net negative surface charge at pH &gt;4. Calculated charge densities agree well withthe results from force-distance studies. We also studied the electrokinetic properties of poly(ethyleneglycol) (PEG) SAMs (HS(CH<SUB>2</SUB>)<SUB>11</SUB>(OCH<SUB>2</SUB>CH<SUB>2</SUB>)<SUB>44</SUB>-OCH<SUB>3</SUB>). All these films show a negative zeta potential inneutral and alkaline solutions which decreases with increasing packing density and optical film thickness,reflecting the changes in frictional properties of the PEG chains with increasing coverage. An explanationwhy the negatively charged (EG<SUB>3</SUB>OMe) surfaces exhibit repulsive electro<br />static forces in aqueous solution,but other negatively charged surfaces do not, is proposed.
Publisher Langmuir
Citation Langmuir 19 (2003) 7380-7385

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