Comparative study of Cu-Zn coatings electrodeposited from sulphate and chloride baths

In this work, the effect of the nature of the salt anion (chloride and sulphate) in the Cu–Zn citrate bath was investigated, using cyclic voltammetry (CV) and chronoamperometry (CA). Experimental electrodeposition parameters (switching potential and imposed potential) were varied in order to examine their influence on the deposits. The coating microstructures were observed by scanning electron microscope (SEM-EDS), the coating phases were characterized by X-ray diffraction (XRD) analysis and the surface composition was assessed by XPS. Higher current efficiency was obtained in chloride baths compared to sulphate baths and best deposits were obtained at −1.4Vvs.(Ag/AgCl/KCl) compared to −1.2 and −1.5Vvs.(Ag/AgCl/KCl). Corrosion test results in 0.5 M NaCl solution show that Cu–Zn deposit produced from chloride bath exhibited the highest corrosion resistance.

Two-Step Nanoscale Approach for Well-Defined Complex Alkanethiol Films on Au Surfaces

Controlling the molecular organization of organic self-assembled monolayers (SAM) is of utmost importance in nanotechnology, molecular electronics, and surface science. Here we propose two well-differentiated approaches, double printing based on microcontact printing (μ-cp) and molecular backfilling adsorption, to produce complex alkanethiol films. The resulting films on model Au surfaces were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Double printing alkanethiols results in clear coexisting regions where no molecular displacement is observed, highlighting the slow diffusion rates of long alkanethiols and large attractive interaction between long alkyl chains. Exposing a single-print μ-cp Au substrate to an additional alkanethiol solution yields the formation of differently ordered domain boundaries with different thickness and micrometer lateral size. The high order is a result of enhanced molecular mobility and restructuring during solution backfilling. The formed molecular assemblies constitute an excellent testing ground for nanoscale phenomena that strongly depend on the nanoscale geometrical and chemical features of the surface such as designed functionality or corrosion initiation and inhibition.

Electrochemical and spectroscopic study of the self-assembling mechanism of normal and chelating alkanethiols on copper

The self-assembly of aliphatic thiol (RSH), dithiol (R(SH)(2)), and dithiocarboxylic acid (RS(2)H) onto mildly oxidized and highly oxidized copper was studied in real time by in situ electrochemical impedance spectroscopy (EIS). Ex situ characterization of the films was carried out using linear sweep voltammetry (LSV), polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), and X-ray photoelectron spectroscopy (XPS). In situ EIS studies found a very fast adsorption of RSH, R(SH)(2), and RS(2)H (within 10-15 s). This fast adsorption step is followed by the long-term additional adsorption and consolidation of SAM. However, the self-assembly of RS(2)H passes through an intermediate step of molecule rearrangement for around 10 to 30 min after around 2 to 7 min of self-assembly. The binding of both sulfur moieties of R(SH)(2) with Cu happens simultaneous. The oxide reduction capacity of RSH, R(SH)(2), and RS(2)H was good. However, the XPS studies showed the decomposition of RS(2)H-based SAMs to Cu(2)S. Monolayers prepared on both mildly oxidized and heavily oxidized Cu with R(SH)(2) had the highest stability. Monolayers of RS(2)H showed the least stability on both mildly oxidized and heavily oxidized Cu. Although RSH-based SAMs had good organization on both mildly oxidized and highly oxidized Cu, R(SH)(2)-based SAMs did not show good organization in either case. The RS(2)H monolayer had good organization only on mildly oxidized Cu.

Tantalum oxide/carbon nanotubes composite coatings on titanium, and their functionalization with organophosphonic molecular films: a high quality scaffold for hydroxyapatite growth

Nowadays, titanium is a very commonly used biomaterial for the preparation of orthopedic and dental implants. Its excellent mechanical and biochemical bulk properties are nevertheless counterbalanced by its propensity to long term degradation in physiological conditions and its weak osseointegrative capacities. In this context, surface modifications can significantly hinder titanium weaknesses. The approach considered in this work relies on the preparation of thin composite coatings based on tantalum oxide and carbon nanotubes by sol-gel process. Tantalum is particularly interesting for its high biocompatibility and bioactivity, as well as its strong resistance to bio-corrosion. Carbon nanotubes are exploited to reinforce the compactness and homogeneity of the coatings, and can act as a favorable factor to strengthen the interaction with bone components by biomimicry. The composite layers are further modified with specific organophosphonic acid molecular films, able to chemically bind the tantalum oxide surface and improve the hydroxyapatite formation process. The characteristics and the qualities of these hybrid inorganic/organic coatings are evaluated by XPS, SEM, TEM, peeling tests, contact angle measurements, and electrochemical characterizations (free potential, polarization curves).

Induction heating vs conventional heating for the hydrothermal treatment of nitinol and its subsequent 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate coating by surface-initiated atom transfer radical polymerization

Nitinol is an alloy of great interest in general and especially in the biomedical field where many researches are aimed to improve both its corrosion resistance and its biocompatibility. In this work, we report on the advantage of an induction heating treatment in pure water compared to a conventional hydrothermal procedure. Both treatments lead to a hydroxylation of the surface, a decrease of the nickel amount in the outer part of the oxide layer, and a drastically decreased corrosion current density. However, the amount of surface hydroxyl groups is higher in the case of the induction heating treatment, which in turn leads to a denser grafting of atom transfer radical polymerization initiators and ultimately to a thicker 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate (MPC) polymer layer than in the case of conventional heating treatments. X-ray photoelectron spectroscopy (XPS), static contact angle, and polarization curves measurements as well as scanning electron microscopy (SEM) have been used to characterize the obtained modified surfaces.

Surface state of carbon nanotubes and Hansen solubility parameters

Carbon nanotubes (CNTs) are often described as insoluble or poorly soluble in organic solvents. In a recent study, we have reported that nonfunctionalized CNTs can be solubilized in suitably chosen organic solvents. Furthermore, their solubility could be understood in terms of the Hansen Solubility Parameters (HSPs). The present work addresses further the question of the CNTs solubility by considering a larger range of solvents. A second part is devoted to the application of the HSPs to two types of functionalized CNTs: oxidized and silanized. These results stress the critical role played by the surface state of the CNTs, on the one hand, and the interest in using the HSPs to guide solubility investigations, on the other hand.

Formation of an adherent polyacrylonitrile/carbon nanotubes composite film onto a polyacrylonitrile brush electrografted on copper

An adherent polymer film based on a composite of polyacrylonitrile/multiwall carbon nanotubes (PAN/MWNTs) have been elaborated on a copper substrate. The first layer is an electrografted PAN brush on which of a subsequent layer of PAN/carbon nanotubes composite has been deposited by simple dipping from solution in dimethylformamide (DMF). MWNTs have been previously chemically functionalized with 3-cyanopropyltrichlorosilane to promote de-bundling and homogeneous dispersion of the carbon nanotubes in the composite.

Note on the dispersion in perfluoropolyether lubricants of multi-walled carbon nanotubes functionalized with (tridecafluoro-1,1 ,2,2-tetrahydrooctyl)trichlorosilane

Multi-walled carbon nanotubes functionalized with F3C-(CF2)5-(CH2)2-SiCl3, a molecule bearing a fluorinated terminal group is found to favor the carbon nanotubes dispersion in three perfluoropolyether fluids (Galden SV70, Fomblin Y25 and Fomblin YR1800). The stability of the suspension appears to be related to the perfluoropolyether viscosity. With respect to time, Fomblin YR1800, the more viscous fluid, leads to the most stable solutions, followed in order by Fomblin Y25 and Galden SV70. In general the smallest particles stay in suspensions. Stability extending over more than one year is observed in the case of Fomblin YR1800.

Comparison between CH3(CH2)15SH and CF3(CF2)3(CH2)11SH monolayers on electrodeposited silver

In this paper, two monolayers self-assembled on a silver substrate are compared: a monolayer of n-hexadecanethiol and a monolayer of n-11-perfluorobutylundecanethiol. The protecting properties of both monolayers have been extensively studied by X-ray photoelectron spectroscopy, contact angle, polarization modulation infrared reflection absorption spectroscopy, conventional electrochemical techniques (polarization curves and electrochemical impedance spectroscopy), and scanning vibrating electrode technique. Both monolayers were successfully self-assembled but organization is slightly different, the fluorinated segment introduces small disorganization. Nevertheless, good homogeneous corrosion protection is observed for each monolayer.