Self-assembled monolayers (SAMs) formed from organic substances can improve the inhibition of metal corrosion, because uniform and closely packed films formed on the metal surface providing an insulating layer1, 2. SAMs on the iron surface are studied so far because iron is one active metal which is easily corroded in the air. In this paper, SECM and SEM have successfully been applied in the study of SAMs inhibition corrosion for iron. SECM has been used to study the electrochemically a… 相似文献
The wire‐like properties of four S‐(4‐{2‐[4‐(2‐phenylethynyl)phenyl]ethynyl}phenyl) thioacetate derivatives, PhC≡CC6H4C≡CC6H4SAc ( 1 ), H2NC6H4C≡CC6H4C≡CC6H4SAc ( 2 ), PhC≡CC6H2(OMe)2C≡CC6H4SAc ( 3 ) and AcSC6H4C≡CC6H4C≡CC6H4SAc ( 4 ) (Figure 1 ), all of which possess a high degree of conjugation along the oligo(phenyleneethynylene) (OPE) backbone, were investigated as self‐assembled monolayers (SAMs) on gold and platinum electrodes by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The redox probe [Fe(CN)6]4? was used in both the CV and impedance experiments. The results indicate that the thiolates derived from thioacetate‐protected precursor molecules 1 and 2 form well‐ordered monolayers on a gold electrode, whereas SAMs derived from 3 and 4 exhibit randomly distributed pinholes. The electron tunnelling resistance and fractional coverage of SAMs of all four compounds were examined using electron tunnelling theory. The analysis of the results reveal that the well‐ordered SAMs of 1 and 2 exhibit higher charge‐transfer resistance in comparison to the defect‐ridden SAMs of 3 and 4 . The additional steric bulk offered by the methoxy groups in 3 is likely to prevent efficient packing within the SAM, leading to a microelectrode behaviour, when assembled on a gold electrode surface. The protected dithiol derivative 4 probably binds to the surface through both terminal groups which prevents dense packing and leads to the formation of a monolayer with randomly distributed pinholes. Atomic force microscopy (AFM) was used to examine the morphology of the monolayers, and height images gave root‐mean‐square (RMS) roughness′s which are in agreement with the proposed SAM structures. 相似文献
The dielectric properties of mixed monolayers of per-(6-amino-2,3-di-O-hexyl) β-CD hydrochloride (NH3-β-CD-OC6) and 1,2 dipalmitoyl, 3-sn-phosphatidic acid (DPPA) have been assessed using surface potential measurements at constant area. From the comparison of these surface potential (ΔV) versus surface density (δ) relationships with those of surface pressure (π) against surface density (δ) it was apparent that the increase in the NH3-β-CD-OC6 content in mixed films gave rise to a gradual increase in the saturation value of the surface potential (ΔVmax). This potential for pure DPPA was found to be equal to 396 mV and for pure CD 554 mV. The ΔVmaxvalues reflect the onset of reorientation effects that arrive at molar areas before the collapse of these films. Independently of reorientation effects, the obtained results strongly indicate that the dipolar term contributing to the overall ΔVvalue was for NH3-β-CD-OC6 due to the hydration of its NH+3group. For both DPPA and NH3-β-CD-OC6 molecules the contribution of the electric double layer (Ψ) was calculated and was found for DPPA and NH3-β-CD-OC6 to be equal to −249 and +252 mV, respectively. These calculated Ψ values made possible the evaluation of dipole moments for NH3-β-CD-OC6 and DPPA monolayers which revealed a marked difference in dipolar properties between these two film forming components. In contrast to DPPA which exhibited a decrease in the surface dipole moment (μ) with the decrease inA, NH3-β-CD-OC6 displayed an increase in μwith the decrease inAforAvalues above 580 Å2. Below this value μdecreases with decreasing molecular area and this variation arises from a change in the polarity of the electric double layer arising from interactions with the complementary anion. The differences in dielectric properties between the two film forming molecules have been attributed to modification, during compression, in the structure of the interfacial water bound to the cyclodextrin. 相似文献
Interfacial proton transfer reactions of pure mercaptoacetic acid (MA) and 2-mercaptobenzothiazole (Mbz) mixed self-assembled monolayers (SAMs) have been studied using a.c. impedance titration method. The charge-transfer resistance (Rct) is measured with the monolayer composition and the ionic strength ofpH solution. The surface pKa can be obtained by the plots of Rct and pH, the reasons of shifts of surface pKa are also explained. 相似文献
In situ techniques are indispensable to understanding many topics in surface chemistry. As a consequence, several spectroscopic methods have been developed to provide molecular‐level information that only spectroscopy can supply. However, as important as this information is, it is just as critical to realize that nearly all surfaces under investigation have spatial heterogeneities of the order of nanometers to millimeters; thus, spatial analysis is very important to the overall interpretation. This Minireview focuses on a few of the recent developments in spectroscopic techniques that can provide spatial, spectroscopic, and in situ information. These techniques include photo‐electron microscopy, infrared and Raman imaging, and nonlinear optical imaging vibrational spectroscopy as applied to topics in corrosion, catalysis and self‐assembled monolayers. 相似文献
Superhydrophobic films mainly based on poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) polyelectrolyte multilayer have been deposited onto cleaned glass substrate by a layer-by-layer dip coating method. 3 bilayers of the PAH and PAA was directly coated onto the substrate as an underlying layer for subsequent coating. Desired surface roughness on the polyelectrolyte bilayers was created by etching the bilayers in hydrochloric acid solution so as to create the open pore having suitable size at the surface. Then, nanoparticles such as SiO2 and TiO2 of various sizes were deposited onto the etched polyelectrolyte bilayers. Finally, the surfaces were further modified with semifluorinated silane followed by cross-linking at 180 °C for 2 h to obtain desirable surface morphological features. The effect of etching time and addition of nanoparticles on surface morphology was investigated using an atomic force microscope (AFM). Wetting ability of the prepared film was determined by measuring water droplet contact angle using a goniometer. Adhesion between the superhydrophobic films and the substrate was evaluated by using a standard tape test method (D3359). The adhesion was improved by reducing the organic content in the films. 相似文献
The self-assembled monolayers (SAMs). which were prepared by spontaneous adsorption of cysteamine on gold surface, were characterized using contact-angle titrations. Contact-angle titration data acquired for the cysteamine SAMs exhibited a smooth transition in contact angle between plateau regions at low and high pH value. The surface pKb, was estimated to be 1.8±0.2, much lower than that in solution. The electroactive azobenzene group was anchored to the monolayer via amide surface reaction. Thus the formed SAMs were further subjected to exchange in dilute pentanethiol soluition. At each stage of modification, the surface was monitored by con-tact-angle titration and cyclic voltanimetry. It was found that the titration curves obviously shifted to the higher contact-angle direction with the increase of surface hydrophobicity. The results are in good agreement with the cyclic voltammetric measurements, demonstrating that the contact-angle titration is a useful technique for monitoring the step by step surface reactions. 相似文献
Functional monolayers : RuII and OsII bis‐terpyridine complexes have been attached through a piperazine‐supported dithiocarbamate to a gold substrate (see picture). The robust tether, and the favourable reduction in oxidation potential induced by the electron‐rich piperazine result in self‐assembled monolayers with excellent reversible redox behaviour and exceptional stability.
Fluorescent noble metal nanoclusters (NCs) are emerging optical nanomaterials with properties similar to those of quantum dots. Their applications can be expanded by combining them with polymer matrices to obtain flexible and transparent light-emitting nanocomposites. However, achieving highly fluorescent nanocomposites of this type remains challenging due to phase separation and aggregation of NCs in polymer hosts leading to a strong reduction in fluorescence efficiency. We address this key issue by covalently grafting a layer of a specifically selected matrix polymer onto a transparent plastic film and photochemically synthesizing the fluorescent metal NCs directly in the grafted layer. The surface-grafted matrix polymer effectively captures the noble metal (Ag) ions, photo-reduces them to atoms, acts as a capping ligand for the growing Ag NCs, and immobilizes them on the substrate surface. The Ag NCs were produced by both wet and dry synthesis, and effects of synthesis method, reaction time, and matrix polymer layer thickness on the fluorescence properties of the resulting nanocomposites were investigated and discussed. Importantly, the fluorescence intensity of these nanocomposite films is sensitive to submicromolar concentrations of aqueous Hg2+ that makes them useful as fluorescent sensing materials for selective and ultrasensitive detection of Hg2+ ions in water. Besides, the nanocomposite films obtained by the dry synthesis of NCs exhibit an intensive emission covering the whole green to red range of the visible spectrum and, hence, produce bright white light under illumination with a blue LED that makes them attractive as down-conversion materials in one-phosphor-converted white LEDs. 相似文献
