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Title: Hydrophobicity-induced drying transition in alkanethiol self-assembled mono-layer water interface
Authors: Lakshminarayanan, V.
Sur, Ujjal Kumar
Keywords: Hydrophobicity
Hydrophobic gap
Self-assembled monolayer
Length scale dependent hydrophobicity
Interfacial capacitance
Uncompensated solution resistance
Issue Date: Aug-2003
Publisher: Indian Academy of Sciences, Bangalore, India.
Citation: Pramana, 2003, Vol. 61, p361-371.
Abstract: During the course of our investigation of the electron transfer properties of some redox species through highly hydrophobic long chain alkanethiol molecules on gold in aqueous and nonaqueous solvents, we obtained some intriguing results such as unusually low interfacial capacitance, very high values of impedance and film resistance, all of which pointed to the possible existence of a nanometer size interfacial gap between the hydrophobic monolayer and aqueous electrolyte. We explain this phenomenon by a model for the alkanethiol monolayer–aqueous electrolyte interface, in which the extremely hydrophobic alkanethiol film repels water molecules adjacent to it and in the process creates a shield between the monolayer film and water. This effectively increases the overall thickness of the dielectric layer that is manifested as an abnormally low value of interfacial capacitance. This behaviour is very much akin to the ‘drying transition’ proposed by Lum, Chandler and Weeks in their theory of length scale dependent hydrophobicity. For small hydrophobic units consisting of apolar solutes, the water molecules can reorganize around them without sacrificing their hydrogen bonds. Since for an extended hydrophobic unit, the existence of hydrogen bonded water structure close to it is geometrically unfavourable, there is a net depletion of water molecules in the vicinity leading to the possible creation of a hydrophobic interfacial gap.
Description: Proceedings of the international conference on liquid crystals and other soft materials held in 2002 at the Raman Research Institute, 2003.
ISSN: 0304-4289
Copyright: Indian Academy of Sciences, Bangalore, India.
Appears in Collections:Research Papers (SCM)

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