Octadecylphosphonic Acid Research Articles

Organic/inorganic Langmuir–Blodgett films based on metal phosphonates 2: zirconium phosphonate-based alternating layer films

Langmuir–Blodgett (LB) films of zirconium salts of the functionalized phosphonic acids 4-octadecyloxyphenylphosphonic acid (P0), 4-octadecyloxybiphenylphosphonic acid (B0), and 4-(4-octadecyloxyphenyldiazenyl)phenylphosphonic acid (A0) have been prepared and characterized. Layers of P0, B0, or A0 can be deposited onto zirconated octadecylphosphonic acid layers using a three-step deposition procedure to form alternating zirconium phosphonate LB bilayers. Film composition and molecular orientations are characterized through X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR).

Atomic Force Microscopy Studies of Microstructure and Properties of Self Assembled Monolayers

Abstract Ex-situ and in-situ studies were performed for self-assembled monolayers (SAMs) formation on mica. The behavior of two surfactants [octadecylphosphonic acid (OPA) and dodecylphosphonic acid (DPA)] in two different solutions [ethanol or tetrahydrofuran (THF)] were studied at different concentrations. A cross section analysis of the monolayer images at partial coverage showed thickness of 1.8 nm, 0.7 nm, and 1.0 nm for OPA, DPA and mixed OPA/DPA, respectively. These values are similar to the ones presented by Xiao and those expected for a monolayer of mixed surfactants as proposed by Whitesides. Since the topography of a monolayer resembles the substrate, the presence of the monolayer at full coverage was determinated by force-distance curve measurements. It was observed that the solvent had the ability to re-dissolve the OPA monolayer, suggesting that the bonding is of a physisorption nature.

Dewetting Modes of Surfactant Solution as a Function of the Spreading Coefficient

The surface coverage of an adsorbed monolayer of octadecylphosphonic acid on mica was varied via solution concentration and immersion time, thereby controlling the surface free energy. For low surface coverage, a stable wetting layer of deposition solution was formed. For slightly greater coverage, the substrate was initially wetted by a thin liquid layer which quickly ruptured, leaving the sample dry. For large coverage, the liquid layer receded from the sample edge. Atomic force microscopy and video microscopy showed that the intermediate regime corresponds to dewetting via nucleation and growth of holes (0.25−5 μm in diameter) in the liquid layer while the dewetting at large coverage proceeds from the sample edge. The dependence of the wetting mode upon surface coverage and solution concentration was explained in terms of a competition between two rates: the nucleation rate of holes in the liquid layer and the speed at which the three-phase line advances.

Kinetics of Self-Assembled Monolayer Growth Explored via Submonolayer Coverage of Incomplete Films

We have studied the growth kinetics of self-assembled monolayers of octadecylphosphonic acid on mica by examining films removed from solution before completion. Atomic force microscope (AFM) images of the quenched films showed islands approximately 2 nm high indicating a growth mechanism consisting of nucleation, growth, coalescence, etc. of dense submonolayer islands. This was consistent with previous in situ AFM studies. Infrared spectroscopy data were consistent with well-ordered alkyl chains and indicated only one type of chain conformation, implying that the areas between islands were bare, not covered with loosely packed disordered molecules. The surface coverage of the submonolayer islands was extracted from AFM images as a function of immersion time for solution concentrations ranging from 0.02 to 2 mM. These data were compared to two common models for adsorption kineticsdiffusion-limited kinetics and adsorption-limited (Langmuir) kinetics. The previously reported quasi-Langmuir−Blodgett deposition process occurring during removal was also taken into account in this modeling. The data were completely inconsistent with the adsorption-limited kinetics and were in reasonable agreement with the functional form for diffusion-limited kinetics. However, the diffusion parameters extracted from the latter fits were much smaller than expected for molecular diffusion in solution and did not scale correctly with solution concentration. We conclude that the island growth is limited by a process that obeys diffusion-like kinetics but not by actual solution diffusion.

Atomic Force Microscopy Studies of Aluminum Corrosion Inhibition by Adsorbed Self Assembled Monolayers

Abstract Atomic force microscopy (AFM) studies on the microstructure of the phosphonic acid (PA) / Al (with native oxide) self assembled monolayer (SAM) system (a possible corrosion resistant coating interface monolayer) has been evaluated as a function of molecular chain length and processing conditions (i.e. adsorption time) in previous works. It was apparent from the AFM topography and phase images of the monolayer microstructure that the octadecylphosphonic acid (OPA) monolyer was the most conformal and showed little dependence on adsorption time (for times ≤ 24 hours). It was therefore chosen as the most promising monolayer compound of the PA/A1 system with which to study corrosion inhibiting properties. In this present work, AFM is used to study the corrosion inhibiting ability of OPA SAMs on aluminum, and also to investigate the “nucleation” and progression of Al corrosion and oxide formation in water at the nanometer level; with and without SAM passivation.

Self-Assembled Monolayers of Alkylphosphonic Acids on Metal Oxides

Dense, highly ordered monolayers can be prepared by the adsorption of octadecylphosphonic acid (ODPA) onto nonporous ZrO2, TiO2, and zirconated silica powders. ODPA reacts strongly with Al2O3 to form a bulk (aluminoalkyl)phosphonate. The infrared spectra of the ODPA monolayers indicate a degree of conformational order comparable to self-assembled monolayers on planar substrates. From the solid-state 31P and 13C NMR spectra, the strength of the surface interaction and the degree of conformational order decrease in the following order: zirconated silica > ZrO2 > TiO2. Although the inner methylenes are primarily in an all-trans conformation, the chain termina are highly disordered. In the case of zirconated silica, there is evidence for the formation of some bulk zirconium alkylphosphonate. Proton line width measurements from 2D WISE NMR experiments reveal that considerable chain mobility is present in the ODPA monolayers on ZrO2 and TiO2, in contrast to bulk crystalline phases.

Self-Assembled Monolayer Growth of Octadecylphosphonic Acid on Mica

Self-assembled monolayers are formed by exposing freshly cleaved mica to a solution of octadecylphosphonic acid in tetrahydrofuran. Atomic force microscope images of samples immersed in solution for varying exposure times show that prior to forming a complete monolayer the molecules aggregate into dense islands (1.8 ± 0.2 nm high) on the surface. The islands have a compact, rounded morphology. The cosine of the contact angle between hexadecane and the partial monolayers has an approximately linear dependence on coverage. However, the cosine of the contact angle of water decreases linearly to about 50% coverage (the percolation threshold of the phosphonate islands) and then appears to saturate.

Thermochromic Properties of Mixture Systems of Octadecylphosphonic Acid and Fluoran Dye

We have examined the thermochromic behavior of thin films formed by mixing a fluoran dye (FD: 2′-( o-chloroanilino)-6′-di- n-butylaminospiro[isobenzofuran-1(3 H),9′-[9 H]xanthene]-3-one) and octadecylphosphonic acid (P18). The coloring and discoloring states were revealed to be controllable by changing the rate of cooling from the colored mixture liquid ( 100°C); quenching at 0°C maintained the solidified colored state, yet discoloring occurred after slow cooling at the rate of 4°C/min. We confirmed by X-ray diffraction and FT-IR spectra that the solidified colored state is produced by formation of the supramolecules, in which seven molecules of P18 and one molecule of FD combined, whose aggregates are in a lamellar structure. In the discoloring state, the supramolecule is decomposed to P18 and FD due to the fractional crystallization of P18.

Molecular self-assembly at a pre-formed Langmuir-Blodgett template

The use of a Langmuir-Blodgett monolayer as a template for subsequent self-assembly of organic molecules from solution has been investigated. The template is formed by transferring a monolayer of octadecylphosphonic acid to a hydrophobic substrate and then binding Zr 4+ ions to the surface from solution. The asymmetric methylene ( v a(CH 2)) band of the template layer appears at 2918 cm −1 and possesses a full width at half-maximum of 20 cm −1 indicating that an all- trans close-packed template is formed. X-ray photoelectron spectroscopy (XPS) analysis of the template layer shows a 1:1 ratio of Zr:P. Octadecylphosphonic acid, 1,10-decadediyldiphosphonic acid (DDPA) and quaterthiophenediphosphonic acid (QDP) have been self-assembled to the template and characterized by attenuated total reflection-Fourier transform IR, XPS and UV-visible techniques. Octadecylphosphonic acid self-assembles to the zirconium template and produces a well-ordered close-packed film as followed by IR analysis. Multilayers of DDPA have been assembled to the template layer; however, the increase in the integrated area of the v a(CH 2) band is not linear with the number of DDPA layers assembled. A rigid diphosphonic acid molecule such as QDP has also been assembled one layer at a time to the template. A plot of UV-visible absorbance vs. the number of layers of QDP shows a linear increase in absorbance after each QDP deposition step.

Single layers of inorganic extended lattices formed at Langmuir-Blodgett templates

Zirconium octadecylphosphonate monolayer and multilayered films have been prepared and characterized by Brewster angle microscopy (BAM), attenuated total reflection-Fourier transform IR spectroscopy, ellipsometry, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). BAM data reveal the rigid nature of a Langmuir monolayer of octadecylphosphonic acid compressed on a Zr 4+ ion subphase; therefore a deposition procedure combining Langmuir-Blodgett (LB) and self-assembly techniques has been developed. First, an octadecylphosphonic acid organic template is prepared by the LB technique and then Zr 4+ ions are self-assembled onto the template from solution. Finally, a capping layer of octadecylphosphonic acid is transferred to the zirconated template to complete the bilayer assembly. The asymmetric methylene stretch frequency υ a(CH 2) appears at 2918 cm −1 and possesses a full width at half-maximum of 20 cm −1 for the template layer, a bilayer and a multilayered film. The position and width of the ν a(CH 2) band indicates that close-packed well-ordered films are formed. Ellipsometry demonstrates a layer-by-layer deposition in multilayered films, while X-ray diffraction proves that the films are indeed layered, possessing a d spacing of 52 Å. XPS analysis of the template layer shows a Zr:P ratio of 1:1 within 10% error, while the bilayer and multilayered films possess a Zr:P ratio of 1:2 consistent with the stoichiometry of the bulk zirconium phosphonates.

Inorganic monolayers formed at an organic template: a Langmuir-Blodgett route to monolayer and multilayer films of zirconium octadecylphosphonate

Single-layer and multilayer films of zirconium octadecylphosphonate have been prepared on silicon oxide surfaces and characterized by Langmuir-Blodgett (LB) transfer data, contact angle, ATR-FTIR, XPS, ellipsometry and X-ray diffraction. The deposition method uses a preformed, organized organic template for assembling the inorganic lattice by combining LB and self-assembly (SA) techniques. First, an LB template of octadecylphosphonic acid is formed on an octadecyltrichlorosilane-covered substrate, then Zr[sup 4+] ions are [open quotes]self-assembled[close quotes] from solution. A capping octadecylphosphonic acid LB monolayer is added to complete the bilayer. Transfer of the phosphonic acid is continuous with transfer ratios ranging between 1.1 and 1.2. Contact angle measurements on a completed bilayer give an advancing contact angle of 112 [plus minus] 1[degrees]. The asymmetric methylene (v[sub a](CH[sub 2])) band remains unchanged in the progression from the template layer to bilayer to multilayers. XPS analysis of the zirconated LB template shows a 1:1 ratio Zr:P, while bilayer and multilayer films possess a Zr:P ratio of 1:2 consistent with the stoichiometry observed in solid zirconium phosphonate. Ellipsometry shows a layer-by-layer increase in film thickness corresponding to a bilayer thickness of 51 [angstrom], while X-ray diffraction reveals a d spacing 52 [angstrom] and thus demonstrates the layered naturemore » of the films. The zirconium phosphonate films are quite insoluble in both water and organic solvents. 51 refs., 8 figs.« less

Patents on videodisc. A Future system almost with us

Combining functional organic self-assembled monolayers (SAMs) with conventional semiconductor materials is a key step in the development of integrated electronics-based devices. T-BAG (Tethering by Aggregation and Growth) has been shown to be a simple and reliable method to grow SAMs of alkylphosphonates on oxide surfaces. However, distinguishing SAMs from ultra-thin multilayers is a challenge for most conventional surface characterization techniques.Self-assembled films of octadecylphosphonic acid (ODPA) were deposited on oxide-covered silicon coupons, converted to the corresponding phosphonates, and characterized by high resolution angularly resolved X-ray photoelectron spectroscopy (XPS). It was our goal to distinguish among different bonding configurations for phosphorous in the phosphonate head groups, namely, mono-dentate, bi-dentate or tri-dentate interactions with the oxide surface, as well as to assess quantitatively the near-surface layer composition.We also present an innovative method that allows us to distinguish between monolayer and multilayer films of ODPA on silicon oxide surfaces. This method is based on differential surface charging effects in XPS. It was found that variation in the ODPA film thickness causes differential responses of various spectral characteristics to an electrical bias applied to the sample during XPS measurements. Both positive and negative applied biases were found to affect the carbon core-level (C1s) line-shape and intensity in the case of the multilayer ODPA film, whereas line-shapes and intensities of all XPS lines measured for the monolayer film were unaffected by the application of a dc bias in the ±30 V range.

Monomolecular films of mixtures: I. Stearic acid with isostearic acid and with tri- p-cresyl phosphate. Comparison of components with octadecylphosphonic acid and with tri- o-xenyl phosphate

Pressure-area isotherms have been obtained for mixed monolayers of pure compounds whose structures are related to those of lubricant additives. Individually, stearic acid and octadecylphosphonic acid with long unbranched chains form strong films. Isostearic acid has a larger molecular area and a much lower collapse pressure than stearic acid. This difference demonstrates the great sensitivity of monolayers to a single methyl side chain. Tri- p-cresyl phosphate and tri- o-xenyl phosphate have much larger areas and lower collapse pressures. An equimolar mixture of two similar compounds, stearic acid and isostearic acid, has monolayer properties close to the calculated average. An equimolar mixture of dissimilar compounds, stearic acid and tri- p-cresyl phosphate, shows film properties of the phosphate at low pressures, expulsion of the phosphate from the monolayer at intermediate pressures, and properties of stearic acid at high pressures.