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Self-assembled monolayers of thiolates on metals as a form of nanotechnology.

The field of self-assembled monolayers (SAMs) has witnessed tremendous growth in synthetic sophistication and depth of characterization over the past 15 years.1 However, it is interesting to comment on the modest beginning and on important milestones. The field really began much earlier than is now recognized. In 1946 Zisman published the preparation of a monomolecular layer by adsorption (self-assembly) of a surfactant onto a clean metal surface.2 At that time, the potential of self-assembly was not recognized, and this publication initiated only a limited level of interest. Early work initiated in Kuhn’s laboratory at Gottingen, applying many years of experience in using chlorosilane derivative to hydrophobize glass, was followed by the more recent discovery, when Nuzzo and Allara showed that SAMs of alkanethiolates on gold can be prepared by adsorption of di-n-alkyl disulfides from dilute solutions.3 Getting away from the moisture-sensitive alkyl trichlorosilanes, as well as working with crystalline gold surfaces, were two important reasons for the success of these SAMs. Many self-assembly systems have since been investigated, but monolayers of alkanethiolates on gold are probably the most studied SAMs to date. The formation of monolayers by self-assembly of surfactant molecules at surfaces is one example of the general phenomena of self-assembly. In nature, self-assembly results in supermolecular hierarchical organizations of interlocking components that provides very complex systems.4 SAMs offer unique opportunities to increase fundamental understanding of self-organization, structure-property relationships, and interfacial phenomena. The ability to tailor both head and tail groups of the constituent molecules makes SAMs excellent systems for a more fundamental understanding of phenomena affected by competing intermolecular, molecular-substrates and molecule-solvent interactions like ordering and growth, wetting, adhesion, lubrication, and corrosion. That SAMs are well-defined and accessible makes them good model systems for studies of physical chemistry and statistical physics in two dimensions, and the crossover to three dimensions. SAMs provide the needed design flexibility, both at the individual molecular and at the material levels, and offer a vehicle for investigation of specific interactions at interfaces, and of the effect of increasing molecular complexity on the structure and stability of two-dimensional assemblies. These studies may eventually produce the design capabilities needed for assemblies of three-dimensional structures.5 However, this will require studies of more complex systems and the combination of what has been learned from SAMs with macromolecular science. The exponential growth in SAM research is a demonstration of the changes chemistry as a disciAbraham Ulman was born in Haifa, Israel, in 1946. He studied chemistry in the Bar-Ilan University in Ramat-Gan, Israel, and received his B.Sc. in 1969. He received his M.Sc. in phosphorus chemistry from Bar-Ilan University in 1971. After a brief period in industry, he moved to the Weizmann Institute in Rehovot, Israel, and received his Ph.D. in 1978 for work on heterosubstituted porphyrins. He then spent two years at Northwestern University in Evanston, IL, where his main interest was onedimensional organic conductors. In 1985 he joined the Corporate Research Laboratories of Eastman Kodak Company, in Rochester, NY, where his research interests were molecular design of materials for nonlinear optics and self-assembled monolayers. In 1994 he moved to Polytechnic University where he is the Alstadt-Lord-Mark Professor of Chemistry. His interests encompass self-assembled monolayers, surface engineering, polymers at interface, and surfaces phenomena. 1533 Chem. Rev. 1996, 96, 1533−1554

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Formation and Structure of Self-Assembled Monolayers.

Using two-phase (water–toluene) reduction of AuCl4– by sodium borohydride in the presence of an alkanethiol, solutions of 1–3 nm gold particles bearing a surface coating of thiol have been prepared and characterised; this novel material can be handled as a simple chemical compound.

Synthesis of thiol-derivatised gold nanoparticles in a two-phase liquid-liquid system

https://is.muni.cz/el/1431/podzim2006/C7780/um/Read/2711172/SAM_str_grwth_ProgSurfSci00_151.pdf

Structure and growth of self-assembling monolayers

Mesoporous silica materials containing functionalized organic monolayers have been synthesized. Solid-state nuclear magnetic resonance suggests that a cross-linked monolayer of mercaptopropylsilane was covalently bound to mesoporous silica and closely packed on the surface. The relative surface coverage of the monolayers can be systematically varied up to 76 percent. These materials are extremely efficient in removing mercury and other heavy metals from both aqueous and nonaqueous waste streams, with distribution coefficients up to 340,000. The stability of these materials and the potential to regenerate and reuse them have also been demonstrated. The surface modification scheme reported here enables rational design of the surface properties of tailored porous materials and may lead to the synthesis of more sophisticated functionalized composites for environmental and industrial applications.

https://science.sciencemag.org/content/sci/276/5314/923.full.pdf

Functionalized Monolayers on Ordered Mesoporous Supports

Spontaneously organized molecular assemblies. 4. Structural characterization of n-alkyl thiol monolayers on gold by optical ellipsometry, infrared spectroscopy, and electrochemistry

Formation and structure of a spontaneously adsorbed monolayer of arachidic on silver

The quantitative aspects of Infrared external reflection spectroscopy (IR-ERS) for the characterlzatlon of thln polymer fibns (<OS pm) on glassy carbon (GC) have been developed. Classical electromagnetlc theory has been appHed to caiculate the mean-square electrlc fleld (MSEF) as a function of angle of Incidence, polarization, and substrate optical properties. These data were used to determine conditions for optlmum Sensitivity. Maximum MSEF occur at 60' from the surface normal for p-polarized llght and at normal Incidence for s-polarlzed light. Spectral band shapes due to the low reflectivity of GC for films of poly(methy1 methacrylate) (PMMA) at GC are severely distorted with respect to those for transmlsslon spectra. For example, the band shape for the carbonyl stretch for a 78-A PMMA film, analyzed with p-polarized irradiation that was lncldent at 60°, Is very asymmetric with an absorption maximum shifted several wavenumbers higher in energy. Irradiation at 20' with spolarlzed light results in derlvative-ilke band shapes that strongly resemble the mirror-Image of the anomalous dlspersion of the real part of the PMMA refractive Index. Integrated absorption strengths for spectra calculated via the parallel layer model for classical electromagnetlc theory agree, In almost every Instance, to within about 7% of those measured; absorbance maxima and minima agree to within 1-2 cm-'. This agreement Indicates that the observed dlstortions restdl from the Inherent d#ferences between ERS and transmlsslon measurements and, more Importantly, demonstrates the quantltatlve capabilities of IR-ERS.

Quantitative Aspects of Infrared External Reflection Spectroscopy: Polymer/Glassy Carbon Interface

Grazing incidence infrared (GI-IR) spectra of spontaneously adsorbed monolayers of arachidic acid on ambient silver surfaces have been recorded. These spectra are very similar to previously obtained measurements on Langmuir - Blodgett (L-B) deposited films prepared from the corresponding carboxylate salts indicating great similarity between the L-B and spontaneously formed films. The acidic head group has reacted with the silver/silver oxide surface to form a carboxylate salt. Additionally, the hydrocarbon chains have assumed a planar zig-zag conformation. These chains are oriented approximately normal to the surface. The spectrum of arachidic acid, CH3(CH2 -) 18COOH, indicates an orthorhombic subcell packing arrangement. Studies with isotopically labeled n-alkanoic acids have been carried out to confirm some mode assignments.

Thomas B. Bright

Papers

Spontaneously organized molecular assemblies. 4. Structural characterization of n-alkyl thiol monolayers on gold by optical ellipsometry, infrared spectroscopy, and electrochemistry

Formation and structure of a spontaneously adsorbed monolayer of arachidic on silver

Quantitative Aspects of Infrared External Reflection Spectroscopy: Polymer/Glassy Carbon Interface

Surface Organization of a Spontaneously Adsorbed Monolayer of Arachidic Acid on Silver