Ethanol macrocluster formation on gold substrate modified with mercapto alcohol

We have recently found that ethanol molecules form hydrogen-bonding molecular macroclusters extending from silanol groups on silica surfaces in nonpolar solvents such as cyclohexane. In this study, we aim at developing a method of forming similar molecular macroclusters on a substrate other than silica modified with hydroxyl groups using the mercapto compounds mercaptoethanol [HS(CH ₂) ₂OH] and 11-mercaptoundecanol [HS(CH ₂) ₁₁OH]. The adsorption of ethanol on these substrates was studied employing surface plasmon resonance (SPR) measurement in ethanol/cyclohexane binary liquids. Adsorption layer thickness was estimated from SPR angle using a five-layer Fresnel equation. For the HS(CH ₂) ₂OH-modified surface, SPR angle decreased by -0.60 ± 0.05° in 1.8 mol % ethanol relative that in cyclohexane, which corresponded to an ethanol adsorption layer of 6.2 ± 0.6nm in the thickness. For the HS(CH ₂) ₁₁OH-modified surface, these values were -0.52 ± 0.03° and 5.2 ± 0.4 nm, respectively.