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 - 1.4 V v s . ( A g / A g C l / K C l ) compared to - 1.2 and - 1.5 V v s . ( A g / A g C l / K C l ) . 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.

Self-assembly mechanism of thiol, dithiol, dithiocarboxylic acid, disulfide and diselenide on gold: an electrochemical impedance study.

The self-assembly mechanism of normal aliphatic thiol (RSH), disulfide (RSSR), diselenide (RSeSeR), dithiol (R(SH)2) and dithiocarboxylic acid (RS2H) onto a gold surface was studied in real time by electrochemical impedance spectroscopy (EIS). The different stages of adsorption could be clearly followed from the interfacial capacitance variation. An initial very fast adsorption, varying from a few seconds to several minutes depending on concentration, is the major adsorption step. This fast step is followed by long-term additional adsorption and self-assembled monolayer (SAM) consolidation. However, an intermediate step, probably due to transformation from the initial physisorbed state to the self-assembled state, could be identified with RSH and R(SH)2. An intermediate rearrangement of RS2H molecules after their initial diffusion controlled Langmuir (DCL) adsorption through the thiol functional group was also recognized. Initial adsorption of RSH and R(SH)2 followed either purely diffusion controlled or DCL kinetics for a very short time. Their continuing fast adsorption followed DCL kinetics. The fast adsorption step of RSSR and RSeSeR also followed the same mechanism. The findings made with EIS on the SAM organization were analyzed by polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). The R(SH)2 based SAMs had comparatively poor organization.

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.

Fabrication of tantalum oxide/carbon nanotubes thin film composite on titanium substrate.

The development of new biomaterials is one of the most challenging tasks in material science. Metals and particularly titanium and its alloys are widely used because of their good corrosion resistance, mechanical properties and biocompatibility. However, the toxicity of alloys, long term degradation in body fluids and risks of loosening are still problematic. To increase the corrosion resistance of the material and reduce ion release, our interest focused on tantalum, another metal well known for its excellent biocompatibility and resistance to bio-corrosion. These very good properties make tantalum a metal of interest for biomaterials but its high cost and high density disqualify it for use as bulk material. In this paper, we propose to combine the good bulk properties of titanium with the excellent surface properties of tantalum by using sol-gel deposition of a tantalum oxide layer on bare titanium. Furthermore, as orthopedics implants are part of our long term goals, we report on the formation of a composite layer of tantalum oxide and multiwalled carbon nanotubes (MWCNTs). MWCNTs have been shown to have promising properties in contact with bone and bone cells and could strengthen the implant. Characterizations are performed using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM).

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.

Titanium modified with layer-by-layer sol-gel tantalum oxide and an organodiphosphonic acid: a coating for hydroxyapatite growth.

Titanium and its alloys are widely used in surgical implants due to their appropriate properties like corrosion resistance, biocompatibility, and load bearing. Unfortunately when metals are used for orthopedic and dental implants there is the possibility of loosening over a long period of time. Surface modification is a good way to counter this problem. A thin tantalum oxide layer obtained by layer-by-layer (LBL) sol-gel deposition on top of a titanium surface is expected to improve biocorrosion resistance in the body fluid, biocompatibility, and radio-opacity. This elaboration step is followed by a modification of the tantalum oxide surface with an organodiphosphonic acid self-assembled monolayer, capable of chemically binding to the oxide surface, and also improving hydroxyapatite growth. The different steps of this proposed process are characterized by surfaces techniques like contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM).

Alkanethiol-oxidized copper interface: the critical influence of concentration.

In this contribution, self-assembled monolayers of n-dodecanethiol (C(12)H(25)SH) at different concentrations on polycrystalline copper have been elaborated. Using XPS, PM-IRRAS, and electrochemical methods (cyclic voltammetry curves and cathodic desorption), the effect of the C(12)H(25)SH concentration on the reduction of the oxide layer has been studied. In all cases, a monolayer of good quality has been obtained. Results provide proof that while the concentration is increased, the thickness of the oxide layer is decreased, to a point that leads to metallic copper for the higher concentration. The results presented in this publication indicate the importance of controlling the interface when forming SAMs of organothiols on oxidizable metals.

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.

Chromosome-breaking activity of extracts of the mushroom Paxillus involutus Fries ex Batsch.

Dry and presoaked seeds of Nigella damascena were treated with aqueous extracts of the mushroom Paxillus involutus. At the first mitosis after the onset of germination, metaphase chromosomes showed damage independent of the origin of the mushrooms. The damaging substance(s) is (are) thermostable. Except a few achromatic gaps, all the lesions observed are of the chromosome type, i.e. are induced at the pre-synthetic G1 stage.

Induction of translocations in mouse spermatogonia after fractionated exposure to 60Co gamma-rays.

Male mice of the Q strain were exposed to 60Co gamma-rays at 2 Gy and 2 X 2 Gy separated by increasing time intervals (from 0 min to 4 min). The chromosome translocations induced in spermatogonia were scored at diakinesis-metaphase I. A significant decrease of the translocation frequency at time intervals higher than 2 min was observed, confirming results obtained with plant materials.

Low doses of pulsed ultrasound and chromosomal abnormalities in male mouse germ cells.

Male mice were exposed to pulsed ultrasound (intensity less than 1 mW, frequency 3.5 MHz) for 30 min or to sham treatment. After 30 h, 11, 12 or 13 days, the testes were cytologically and histologically examined (using squash preparations, air-drying and sections). The resulting damage was studied at diakinesis-metaphase I and II, spermatogonial metaphase and anaphase. The investigation by air-drying did not show any significant increase in chromosome damage, 30 h, 11, 12 and 13 days after treatment (spermatogonial and spermatocytic metaphases). There was, however, a significant increase of the frequency of aneuploid cells detected at metaphase II. Investigations by squash techniques or sections did not reveal adverse effects on the spindles at spermatogonial and spermatocytic anaphases. We suggest that the reduction of fertility previously observed in our clinic could be explained by an increase of aneuploidy if germ cells are exposed to ultrasound during diakinesis of the first meiotic division.

In vivo mutagenicity evaluation of domperidone in Drosophila germ cells and rat bone marrow cells.

Possible induction of chromosome aberrations and gene mutations by domperidone was studied in vivo respectively by a micronucleus test on female rats and a sex-linked recessive lethal test on Drosophila. In accordance with previous results all these studies revealed negative findings for domperidone so that it can be concluded that domperidone has no potential to induce chromosome aberrations and/or gene mutations.