Octadecanethiol Molecules Research Articles

Superhydrophobic ODT-TiO2 NW-PDA nanocomposite-coated polyurethane sponge for spilled oil recovery and oil/water separation

Frequent occurrences of accidental oil spills, chemical leakages and oily water discharge make the development of effective and efficient methods for spilled oil and organic pollutants clean-ups extremely critical and urgent. Here, a novel superhydrophobic octadecanethiol-TiO2 nanowires-polydopamine nanocomposites-modified polyurethane sponge was fabricated by a facile and cost-effective synthesis process, wherein, self-polymerization of dopamine was coated on the polyurethane skeleton structure, followed by direct incorporation of TiO2 nanowires to enhance surface roughness and lastly, surface coating with the low surface energy octadecanethiol molecules. The resultant PU-PDA-TiO2-ODT sponge showed superhydrophobic and superoleophilic with the water contact angle (WCA) of 154.0 ± 2° and the oil contact angle of 0°, as well as self-cleaning and anti-fouling capabilities. The as-fabricated sponge demonstrated high oil adsorption capacity for a broad variety of oils and organic solvents, also exhibiting good reusability of more than 30 cycles without diminishing adsorption performance. The potential for practical applications was demonstrated through gravity-driven and vacuum assisted continuous separations, yielding more than 99.9% oil purity. Moreover, the as-prepared sponge exhibited superior mechanical strength through exceptional performance in compression, ultrasonication and frictions tests, and consistent superhydrophobicity in harsh environments including exposure to pH, temperature and NaCl concentration variations. Thus, the novel superhydrophobic and superoleophilic sponge has great potential for practical application in oil-water separations.

AFM imaging and plasmonic detection of organic thin-films deposited on nanoantenna arrays

In this study, atomic force microscopy (AFM) imaging has been used to reveal the preferential deposition of organic thin-films on patterned nanoantenna array surfaces - identifying the localised formation of both monolayer and multilayer films of octadecanethiol (ODT) molecules, depending on the concentration of the solutions used. Reliable identification of this selective deposition process has been demonstrated for the first time, to our knowledge. Organic thin-films, in particular films of ODT molecules, were deposited on plasmonic resonator surfaces through a chemi-sorption process - using different solution concentrations and immersion times. The nanoantennas based on gold asymmetric-split ring resonator (A-SRR) geometries were fabricated on zinc selenide (ZnSe) substrates using electron-beam lithography and the lift-off technique. Use of the plasmonic resonant-coupling technique has enabled the detection of ODT molecules deposited from a dilute, micromolar (1 μM) solution concentration - with attomole sensitivity of deposited material per A-SRR – a value that is three orders of magnitude lower in concentration than previously reported. Additionally, on resonance, the amplitude of the molecular vibrational resonance peaks is typically an order of magnitude larger than that for the non-resonant coupling. Fourier-transform infrared (FTIR) spectroscopy shows molecule specific spectral responses – with magnitudes corresponding to the different film thicknesses deposited on the resonator surfaces. The experimental results are supported by numerical simulation.

Grain Structures and Boundaries on Microcrystalline Copper Covered with an Octadecanethiol Monolayer Revealed by Sum Frequency Generation Microscopy.

An octadecanethiol (ODT) self-assembled monolayer on microcrystalline copper was investigated by sum frequency generation (SFG) imaging microscopy. The crystal grain and grain boundaries of the copper surface were mapped in the SFG image based on the strong brightness contrast of the SFG signal across the boundary. Local SFG spectra reveal significant difference with each other as well as the average SFG spectra, indicating the heterogeneity of the copper surface resulting from copper grains with distinct crystallographic facets and orientations. It is demonstrated that the SFG signal of crystalline domain areas contains azimuthal anisotropy with respect to the plane of incidence. In addition, the statistical orientation analyses of amplitude ratio of CH3-sym/CH3-asym and corresponding contour maps imply that the orientation of ODT molecules is affected by the underlying copper.

In Situ Vibrational Study of the Reductive Desorption of Alkanethiol Monolayers on Gold by Sum Frequency Generation Spectroscopy

In situ sum frequency generation vibrational spectroscopy (SFG) was used to monitor the reductive desorption of decanethiol (DT) and octadecanethiol (ODT) self-assembled monolayers (SAMs) grown on evaporated gold on silica. At negative potentials, the alkyl chains of both monolayers became disordered as monitored by the appearance of methylene symmetric stretching modes in the collected spectra. The increased tilting of the terminal methyl groups on the chains of the DT monolayer further support this observation. The disappearance of the methyl C–H stretching vibrational modes at the reductive potential suggests that DT molecules diffused away from the surface after reduction. ODT molecules, on the other hand, retained their two-dimensional structure near the gold surface, implied by the strong methyl vibrational modes at the reductive potential. After four reductive cycles, a large portion of the DT SAM was fully desorbed, while the ODT monolayer existed as a combination of physisorbed and chemisorbed mo...

Directed assembly of nanodiamond nitrogen-vacancy centers on a chemically modified patterned surface.

Nitrogen-vacancy (NV) centers in nanodiamond (ND) particles are an attractive material for photonic, quantum information, and biological sensing technologies due to their optical properties-bright single photon emission and long spin coherence time. To harness these features in practical devices, it is essential to realize efficient methods to assemble and pattern NDs at the micro-/nanoscale. In this work, we report the large scale patterned assembly of NDs on a Au surface by creating hydrophobic and hydrophilic regions using self-assembled monolayer (SAM). Hydrophobic regions are created using a methyl (-CH3) terminated SAM of octadecanethiol molecules. Evaporating a water droplet suspension of NDs on the SAM patterned surface assembles the NDs in the bare Au, hydrophilic regions. Using this procedure, we successfully produced a ND structures in the shape of dots, lines, and rectangles. Subsequent photoluminescence imaging of the patterned NDs confirmed the presence of optically active NV centers. Experimental evidence in conjunction with computational analysis indicates that the surface wettability of the SAM modified Au surface plays a dominant role in the assembly of NDs as compared to van der Waals and other substrate-ND interactions.

Interaction of Alkanethiols with Nanoporous Cluster-Assembled Au Films

This article presents a study of the interaction of octadecanethiol molecules (C(18)) with nanoporous cluster-assembled gold films under a liquid environment based on a combined spectroscopic ellipsometry and X-ray photoelectron spectroscopy investigation. By comparing the optical response, following the deposition of C(18), of cluster-assembled films with varying degrees of porosity with that of flat surfaces and by resolving the corresponding features of the molecule-Au bond, we have been able to define the conditions that either favor molecular in-depth diffusion into the pores or promote the formation of a molecular self-assembled monolayer (SAM) restricted to the film surface. In the presence of abundant open pores, C(18) molecules strongly diffuse within the film interior and bind to the pore walls, whereas in the presence of porous films with less abundant open pores we have observed that the molecules tend to remain confined to the surface region, adopting a SAM-like configuration.

Self-Assembled Monolayers of Alkanethiols on InAs

We describe the deposition and properties of self-assembled monolayers (SAMs) of methyl-terminated alkanethiols on InAs(001) surface. For these model hydrophobic films, we used water contact angle measurements to survey the preparation of alkanethiol monolayers from base-activated ethanolic solutions as a function of the solution and deposition parameters, including chain length of alkanethiols, deposition time, and solution temperature and pH. We then used X-ray photoelectron spectroscopy (XPS), ellipsometry, and electrochemistry to characterize the composition and structure of octadecanethiol (ODT) monolayers deposited on InAs under optimized conditions. When applied to a thoroughly degreased InAs(001) wafer surface, the basic ODT solution removes the native oxide without excessively etching the underlying InAs(001) substrate. The resulting film contains approximately one monolayer of ODT molecules, attached to the InAs surface almost exclusively via thiolate bonds to In atoms, with organic chains extended away from the surface. These ODT monolayers are stable against degradation and oxidation in air, organic solvents, and aqueous buffers. The same base-activated ODT treatment can also be used to passivate exposed InAs/AlSb quantum well (QW) devices, preserving the unique electronic properties of InAs surfaces and allowing the operation of such passivated devices as continuous flow pH-sensors.

Langmuir–Blodgett films of octadecanethiol – properties and potential applications

Octadecanethiol (ODT) is known to form self-assembled monolayer on noble metal surfaces which has potential technological applications. Langmuir–Blodgett (LB) technique is another useful method of obtaining highly ordered assembly of molecules. It is of interest to find whether ODT molecules can also form a stable Langmuir monolayer which facilitates the preparation of LB films. In literature, it has been reported that ODT molecules form an unstable Langmuir monolayer. We have studied the stability of the monolayer of the ODT molecules at air–water interface using surface manometry and microscopy techniques. We find the monolayer to be stable on ultrapure water of resistivity greater than 18 MΩ cm. However, the behavior changes in the presence of even small amount of additives like NaOH or CdCl 2 in the subphase. Our AFM studies on the LB films of ODT deposited from ion-free ultrapure water showed streak-like bilayer domains. The LB films of ODT deposited from CdCl 2 containing aqueous subphase yield dendritic domains of the complexed unit grown over ODT monolayer. These nanostructures on surfaces may have potential applications in molecular electronics.

Quantitative electrostatic force microscopy on heterogeneous nanoscale samples

Locally resolved electrostatic force spectroscopy is combined with Kelvin force microscopy to compare the results obtained using either the force or the frequency as signal source for tip-sample interaction. A two-component locally heterogeneous sample—islands of octadecanethiol molecules self-assembled on Au(111)—is used as a nanometer scale model system. On this kind of sample, electrostatic force spectroscopy as well as Kelvin force microscopy clearly demonstrate that local and quantitative electrostatic force microscopy has to be implemented with the frequency as the signal source.

Preparation of Alkanethiol Monolayers on Mild Steel Surfaces Studied with Sum Frequency Generation and Electrochemistry

An n-alkanethiol, octadecanethiol (ODT), monolayer was successfully prepared onto an oxide-free mild steel (MS) surface under cathodic polarization in a 0.1 M LiCl/CH(3)OH solution containing 1 mM ODT. Cyclic voltammetry (CV) and electrochemical impedance (EIS) and sum frequency generation (SFG) spectroscopy were applied to study and characterize the adsorption of ODT at a MS surface. In 0.1 M LiCl/CH(3)OH solution containing 1 mM ODT, CV of the MS electrode shows a dramatic decrease in charging current and a positive shift in oxidation potential when compared to a solution without ODT. The interfacial capacitance was obtained as 2.52 microF/cm(2) from the impedance data. An average chain tilt angle of 48 degrees for the ODT molecules was deduced from the comparison of the interfacial capacitances of the ODT/MS and ODT/Au monolayers. X-ray photoelectron spectroscopy confirmed the formation of the ODT monolayer on mild steel. The ppp SFG spectrum of the ODT-modified MS features three strong methyl vibrational modes at 2877, 2943, and 2967 cm(-1), indicating the formation of the oriented and densely packed ODT monolayer. However, the appearance of the two weak CH(2) groups' vibrational modes at 2850 and 2914 cm(-1) implies the presence of defects in the ODT monolayer. ODT/Au films were prepared to compare with the ODT/MS films. Orientation analysis of the air/solid interface suggests that the methyl group of ODT/Au films has a tilt angle of 30 degrees , while the methyl group of ODT/MS films has a tilt angle of 23 degrees . Water was found to have an impact on the shape of the SFG spectra of ODT/MS. This suggests that the solution penetrated through the defects to reach the MS surface.

Tribological behavior of self-assembled double layer measured by a pin-on-plate method

We investigated the frictional properties and the durability of self-assembled double layers using pin-on-plate methods and X-ray photoelectron spectroscopy (XPS). We found that double layers made from octadecanethiol (ODT) and mercaptohexadecanoic acid (MHA) connected via Cu ions exhibited lower frictional coefficients (approximately 0.1–0.15) than that of ODT monolayer (∼0.2). XPS measurements revealed that ratios of C(1s)/Au(4f) after friction tests were lower than that before friction but was higher than that measured on ODT monolayer, suggesting that some of ODT molecules were desorbed from the surface, i.e. formation of loosely packing molecular layers after friction. These findings suggest that the loosely packed molecular layer contributed to decrease the friction.

In situ UV–visible and IR absorption study of the aggregation of silver colloidal particles via chemisorption of octadecanethiol

AbstractAggregation of silver colloidal particles in the hydrosol via chemisorption of octadecanethiol (ODT) molecules was investigated based on in situ UV–visible transmission and infrared attenuated total reflection (ATR) measurements. As‐prepared silver hydrosol exhibits a single absorption peak at 395 nm because of the plasma resonance of the metal particles. Upon addition of ODT‐dissolved ethanol to the hydrosol, the resonance band red‐shifts and broadens, the detailed features of which depend on the ODT concentration and elapsed time. Both the red‐shift and the broadening are attributed to particle aggregation in the solution via ODT chemisorption. Aggregation on a germanium prism surface by the addition of ODT‐dissolved ethanol to the hydrosol was investigated using infrared ATR spectroscopy. At moderate ODT concentrations, intense aggregation via ODT chemisorption occurs strongly on the prism surface, allowing observation of ODT absorption bands. Angle‐dependent infrared ATR measurements for the ethanol and ODT molecules at the prism/solution interface clearly show that aggregation on the prism surface proceeds via the exclusion of ethanol. Copyright © 2004 John Wiley & Sons, Ltd.

A Novel Nanolithography Technique for Self-Assembled Monolayers Using a Current Sensing Atomic Force Microscope

A nanolithography technique for a self-assembled monolayer (SAM) using a current sensing atomic force microscope (CSAFM) is proposed. Using this method, we prepared nanometer-sized patterns on the octadecanethiol SAM by removing octadecanethiol molecules at a force of a few nanonewtons in toluene when an appropriate positive or negative bias was applied. The relation between the pattern formation and the applied bias was studied at both positive and negative polarizations. The minimum pattern size achieved by this method was 15 nm. The formation probability as a function of the applied force and the trace amount of water contained in toluene was also systematically investigated. These results suggested an electrochemical mechanism for the removal of thiol molecules.

Molecular Dynamics Study of Partial Monolayer Ordering of Chain Molecules

We present the results of a molecular dynamics study of a partial monolayer of self-assembled octadecanethiol molecules. The correlations between various statistical measures of surface induced chain ordering are examined. These include the density profile, chain morphology, tilt angle distributions, and gauche defect distributions. Particular attention is focused on the significance of the strength of the alkane chain surface interaction, as well as the role of temperature, on the type and degree of disorder which we observe. Our simulations are in accord with experimental evidence which indicates that the quality, in the sense of reproducibility in the laboratory, of dense films increases as the coupling of the chain molecules with the surface decreases. We believe that our findings have general implications for the establishment of experimental protocols for self-assembled surface films of organic molecules with varying degrees of prescribed disorder.

Phase Transfer of Aqueous Gold Colloidal Particles Capped with Inclusion Complexes of Cyclodextrin and Alkanethiol Molecules into Chloroform

Colloidal gold particles synthesized in water have been capped with octadecanethiol (ODT) molecules rendered water-soluble by threading with α-cyclodextrin (α-CD) molecules. Thereafter, the gold nanoparticles could be transferred into an organic solvent such as chloroform by vigorous shaking of a biphasic mixture of the α-CD-threaded ODT-stabilized gold hydrosol and chloroform. The phase transfer of the gold nanoparticles could be observed as a rapid transfer of color from the aqueous phase to the organic phase. During shaking of the biphasic mixture, it is believed that α-CD molecules are dislodged from the octadecanethiol molecules, rendering the gold particles hydrophobic and amenable to phase transfer. Transmission electron microscopy studies of films of the gold nanoparticles in chloroform formed by solvent evaporation indicate a uniform size distribution of the nanoparticles and hexagonal close-packing of the particles in the film.

Studies of Adsorption Kinetics and Defects of Self‐Assembled Thiol Monolayers on Gold by Capacitance Plane Plot

AbstractThe capacitive property of an electrode/electrolyte interface can be described by complex capacitance. The capacitance plane plots (CPPs) of ideal polarized and kinetic controlled electrodes are derived based on the concept of complex capacitance. By using CPPs, the capacitance of electrode/electrolyte interface can be conveniently determined. In this work, CPPs obtained in ac impedance experiments are employed for the first time in studying the kinetics of adsorption process of the thiol monolayer. The coverage of octadecanethiol (ODT) monolayer on gold is examined as a function of adsorption time. The adsorption process of ODT molecules on gold exhibits two distinct phases: an initial rapid step followed by a slow one. The simple Langmuir model best explains our experimental data in the initial adsorption stage. CPPs and cyclic voltammetry (CV) indicate that, in the initial adsorption step, the ODT monolayer contains defects whose number decreases with the increasing of adsorption time.

Phase Transfer of Aqueous CdS Nanoparticles by Coordination with Octadecanethiol Molecules Present in Nonpolar Organic Solvents

The transfer of CdS nanoparticles of dimensions 60 A synthesized in an aqueous environment into petroleum ether (pet ether) by coordination of the nanoparticles with octadecanethiol (ODT) molecules present in the organic phase is described. The phase transfer of the CdS nanoparticles into pet ether occurs extremely rapidly during vigorous stirring of the biphasic mixture (CdS-in-water/ODT-in-pet ether). Hydrophobization of the CdS nanoparticles due to surface coordination of ODT facilitates the phase transfer process. The hydrophobized CdS nanoparticles may be precipitated and redispersed in different nonpolar organic solvents without an apparent distortion in the particle size distribution. Close-packed CdS nanoparticle thin films were formed by immersion of suitable substrates in the organic solutions and evaporation of the organic component. The CdS nanoparticles have been characterized at different stages of the synthesis procedure using UV−vis spectroscopy, Fourier transform infrared (FTIR) spectrosc...

Solvent trapping during the self-assembly of octadecanethiol monolayer on roughened gold electrodes from surface-enhanced Raman scattering studies

Abstract The possibility of solvent molecules being trapped within the monolayer interior during the self-assembly of octadecanethiol molecules on gold was investigated by means of surface-enhanced Raman scattering (SERS). The monolayers were self-assembled from acetonitrile solution. The rationale behind the choice of this particular solvent was its characteristic strong band in the SERS spectrum around 2250 cm −1 , where there are no Raman bands in the spectra of alkanethiols. With the example of acetonitrile, we point out the possibility of trapping molecules of the solvent from which the monolayer self-assembly is carried out. Traces of solvent molecules within the monolayer can affect the electrochemical behaviour of monolayer-modified electrodes.

Two-dimensional ordering of octadecanethiol molecules on graphite observed by scanning tunneling microscope

Molecular-resolution images of n-octadecanethiol monolayer molecules on a graphite substrate are successfully observed with a scanning tunneling microscope (STM) in air. The images reveal that the molecules arrange in a hexagonal p(3 × 3) structure with a periodicity of 7.5 Å, a feature associated with the graphite substrate. X-ray photoelectron spectroscopy studies suggest that the methyl terminal group is adsorbed on the graphite. A model for the possible arrangement of the molecules on graphite surfaces is proposed.

Three-probe voltammetric characterisation of octadecanethiol self-assembled monolayer integrity on gold electrodes

Abstract The passivating behaviour of self-assembled octadecanethiol monolayers on polycrystalline gold electrodes was tested by means of the cyclic voltammetry technique in the presence of three different redox probe molecules. The three compounds chosen for this purpose, ruthenium hexamine chloride [Ru(NH 3 )Cl 3 ], potassium ferrocyanide [K 4 Fe(CN) 6 ] and benzoquinone, were selected on the basis of the differences in their heterogeneous electron transfer rate constants and their hydrophobic/hydrophilic character. Our studies show that passivating properties of octadecanethiol monolayers against these probes are different. The results obtained are discussed in terms of Tafel approach and monolayer integrity. It appears that the screening of self-assembled films with different probes is necessary in order to properly characterise the film integrity and passivating behaviour. Additionally, the interaction of octadecanethiol molecules with a polycrystalline gold surface was evaluated by means of potentiostatic pulse measurements.