Advances in Polymeric Neutron Shielding: The Role of Benzoxazine-h-BN Nanocomposites in Nuclear Protection.

Given their substantial neutron capture cross-section, extreme hardness, and high chemical and thermal stability, boron-based materials are widely used as building blocks to protect against highly ionizing radiations such as gamma rays and neutrons. Indeed, uncontrolled nuclear radiation exposure can be highly hazardous to radiation workers and the public. In this sense, this work presents an extensive study and experimental evaluation of the nuclear shielding features of hexagonal-boron nitride (h-BN) based nanocomposite, where bisphenol-A based polybenzoxazine (BA-PBz) was used as matrix. The neutron shielding studies were carried out at the nuclear research reactor of Algeria NUR. The surface treatment of h-BN nanoparticles was confirmed by FTIR and XPS techniques. The curing behavior and the degradation phenomena of the nanocomposites were evaluated by DSC-TGA analyses. The distribution of h-BN nanoparticles within the polymer matrix was assessed by TEM and SEM. The results showed that the developed boron nitride-based nanocomposite exhibits intriguing shielding performances and good thermal stability. The DSC-TGA tests exhibit high degradation temperature that reach 279°C. The highest performances were obtained at an h-BN concentration of 7 wt%, where the macroscopic cross was found to be (Σ = 3.844 cm-1) with a screening ratio of (S = 96.12%), equivalent to a mean free path (λ) of 0.138 cm.

Pulsed electrodeposition of Ag+ doped prosthetic Fluorohydroxyapatite coatings on stainless steel substrates.

In order to reinforce the antibacterial character of fluorohydroxyapatite (FHA) prosthetic layers on 316L stainless steel (316L SS), Ag+ ions (an antibacterial agent) are included in the electrodeposition medium to be incorporated in the FHA layers created by pulsed protocol. The doped coatings (Ag-FHA) with different concentrations of silver ions (5, 10, 20, 40 and 100 ppm) were characterized electrochemically (polarization curves and electrochemical impedance spectroscopy) in simulated body fluid (SBF) solution and microbiologically against two pathogenic bacteria (Staphylococcus aureus and Escherichia coli). XPS, EDX and Raman spectroscopies were used to complement these evaluations. Whatever the concentration of incorporated Ag+ ions, the FHA morphology, structure and composition are not affected. The XPS and EDX results confirm the Ag+ presence within the apatite crystals, mostly concentrated at the extreme surface of the coatings. They also show the lowering of the stoichiometry of the coatings, confirmed by Raman analyses. The corrosion studies indicate that the prosthetic coatings act as a barrier against corrosion of the 316L SS alloy. Moreover, the results of the microbiological tests show that a content of 40 ppm of silver, introduced into the prosthetic coatings, inhibits the bacterial growth. Lower concentrations showing only a partial inhibition. In conclusion, using a pulsed current mode in the electrodeposition processes generates Ag-FHA/316L SS systems suitable for biomedical applications.

Polypyrrole-Wrapped Carbon Nanotube Composite Films Coated on Diazonium-Modified Flexible ITO Sheets for the Electroanalysis of Heavy Metal Ions.

Highly sensitive multicomponent materials designed for the recognition of hazardous compounds request control over interfacial chemistry. The latter is a key parameter in the construction of the sensing (macro) molecular architectures. In this work, multi-walled carbon nanotubes (CNTs) were deposited on diazonium-modified, flexible indium tin oxide (ITO) electrodes prior to the electropolymerization of pyrrole. This three-step process, including diazonium electroreduction, the deposition of CNTs and electropolymerization, provided adhesively-bonded, polypyrrole-wrapped CNT composite coatings on aminophenyl-modified flexible ITO sheets. The aminophenyl (AP) groups were attached to ITO by electroreduction of the in-situ generated aminobenzenediazonium compound in aqueous, acidic medium. For the first time, polypyrrole (PPy) was electrodeposited in the presence of both benzenesulfonic acid (dopant) and ethylene glycol-bis(2-aminoethylether)-tetraacetic acid (EGTA), which acts as a chelator. The flexible electrodes were characterized by XPS, Raman and scanning electron microscopy (SEM), which provided strong supporting evidence for the wrapping of CNTs by the electrodeposited PPy. Indeed, the CNT average diameter increased from 18 ± 2.6 nm to 27 ± 4.8, 35.6 ± 5.9 and 175 ± 20.1 after 1, 5 and 10 of electropolymerization of pyrrole, respectively. The PPy/CNT/NH2-ITO films generated by this strategy exhibit significantly improved stability and higher conductivity compared to a similar PPy coating without any embedded CNTs, as assessed by from electrochemical impedance spectroscopy measurements. The potentiometric response was linear in the 10-8-3 × 10-7 mol L-1 Pb(II) concentration range, and the detection limit was 2.9 × 10-9 mol L-1 at S/N = 3. The EGTA was found to drastically improve selectivity for Pb(II) over Cu(II). To account for this improvement, the density functional theory (DFT) was employed to calculate the EGTA-metal ion interaction energy, which was found to be -374.6 and -116.4 kJ/mol for Pb(II) and Cu(II), respectively, considering solvation effects. This work demonstrates the power of a subtle combination of diazonium coupling agent, CNTs, chelators and conductive polymers to design high-performance electrochemical sensors for environmental applications.

A novel and sensitive hexadecyltrimethylammoniumbromide functionalized Fe decorated MWCNTs modified carbon paste electrode for the selective determination of Quercetin.

The fabrication of differential pulse voltametry (DPV) sensor for the effective detection of Quercetin (QR) was achieved by modifying carbon paste electrode (CPE) with Iron decorated multi walled carbon nano tubes (Fe-MWCNTs) followed by drop casting of hexadecyltrimethylammonium bromide onto the surface for optimal results. Cyclic voltammetry and DPV techniques were used for qualitative and quantitative analysis of QR (Quercetin) respectively. The sensor revealed impressive electro-catalytic behavior towards oxidation of QR with almost 6.4 times increase in current compared to bare carbon paste electrode CPE and also decrease in the energetics. Under optimum conditions, a wide linear dynamic range of 0.06 to 3000µM, with a lower limit of detection, 1.20nM with S/N=3 was observed. Absence of peak for the interfering molecules such as Folic acid and Ascorbic acid makes it a unique sensor with significant analytical advantage. The quantification of QR at this sensor was not affected by the presence of 1000 fold Uric Acid implying that the sensor is capable of specifically identifying QR in a mixture of interfering molecules. In this paper, we demonstrate that with minimal use of modifiers and simple procedures of fabrication, the fabricated sensor exhibits excellent stability, reproducibility and swift responses. Application of the developed electrode was demonstrated by detecting QR in wine and coconut water samples with satisfactory recoveries.

Electroassisted Functionalization of Nitinol Surface, a Powerful Strategy for Polymer Coating through Controlled Radical Surface Initiation.

Coating Nitinol (NiTi) surfaces with a polymer layer has become very appealing in the past few years owing to its increased attraction in the biomedical field. Although its intrinsic properties helped ensure its popularity, its extensive implementation is still hampered by its nickel inclusion, making it sensitive to pitting corrosion and therefore leading to the release of carcinogenic Ni2+ ions. Among all recent ways to modify NiTi surfaces, elaboration of self-assembled monolayers is of great interest as their high order confers a reinforcement of the metal surface corrosion resistance and brings new functionalities to the metal for postmodification processes. In this work, we compare the electroassisted and thermally assisted self-assembling of 11-(2-bromoisobutyrate)-undecyl-1-phosphonic acid (BUPA) to the classical immersion process on NiTi surfaces initially submitted to a hydrothermal treatment. Among all tested conditions, the electroassisted grafting of BUPA at room temperature appears to be the most promising alternative, as it allows grafting in very short times (5-10 min), thus preventing its degradation. The thus-formed layer has been proven to be sufficient to enable the surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-(dimethylamino)ethyl methacrylate.

Iron nanoparticles decorated multi-wall carbon nanotubes modified carbon paste electrode as an electrochemical sensor for the simultaneous determination of uric acid in the presence of ascorbic acid, dopamine and L-tyrosine.

Iron nanoparticles decorated multi-wall carbon nanotubes modified carbon paste electrode (Fe-MWCNTs/MCPE) was prepared by bulk-modification method. The electrochemical impedance spectroscopy (EIS) suggests least charge transfer resistance at the modified electrode. The electrochemical behavior of UA was studied in 0.1M phosphate buffer solution (PBS) of pH3.0 using cyclic voltammetry (CV) while differential pulse voltammetry (DPV) was used for quantification. The spectroelectrochemial study of oxidation of UA at Fe-MWCNTs/MCPE showed a decrease in the absorbance of two peaks with time, which are ascribed to π to π(⁎) and n to π(⁎) transitions. Under optimum condition, the DPV response offered two linear dynamic ranges for UA in the concentration range 7.0×10(-8)M-1.0×10(-6)M and 2.0×10(-6)M-1.0×10(-5)M with detection limit (4.80±0.35)×10(-8)M (S/N=3). The practical analytical application of this sensor was successfully evaluated by determination of spiked UA in clinical samples, such as human blood serum and urine with good percentage recovery. The proposed electrochemical sensor offers a simple, reliable, rapid, reproducible and cost effective analysis of a quaternary mixture of biomolecules containing AA, DA, UA and Tyr which was free from mutual interferences.

Synergistic effect on corrosion resistance of Phynox substrates grafted with surface-initiated ATRP (co)polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) and 2-hydroxyethyl methacrylate (HEMA).

Phynox is of high interest for biomedical applications due to its biocompatibility and corrosion resistance. However, some Phynox applications require specific surface properties. These can be imparted with suitable surface functionalizations of its oxide layer. The present work investigates the surface-initiated atom transfer radical polymerization (ATRP) of 2-methacryloyoxyethyl phosphorylcholine (MPC), 2-hydroxyethyl methacrylate (HEMA), and ATRP copolymerization of (HEMA-co-MPC) (block and statistic copolymerization with different molar ratios) on grafted Phynox substrates modified with 11-(2-bromoisobutyrate)-undecyl-1-phosphonic acid (BUPA) as initiator. It is found that ATRP (co)polymerization of these monomers is feasible and forms hydrophilic layers, while improving the corrosion resistance of the system.

Pristine multi-walled carbon nanotubes/SDS modified carbon paste electrode as an amperometric sensor for epinephrine.

An amperometric sensor for the determination of epinephrine (EP) was fabricated by modifying the carbon paste electrode (CPE) with pristine multi-walled carbon nanotubes (pMWCNTs) using bulk modification followed by drop casting of sodium dodecyl sulfate (SDS) onto the surface for its optimal potential application. The modified electrode showed an excellent electrocatalytic activity towards EP by decreasing the overpotential and greatly enhancing the current sensitivity. FE-SEM images confirmed the dispersion of pMWCNTs in the CPE matrix. EDX analysis ensured the surface coverage of SDS. A comparative study of pMWCNTs with those of oxidized MWCNTs (MWCNTsOX) modified electrodes reveals that the former is the best base material for the construction of the sensor with advantages of lower oxidation overpotential and the least background current. The performance of the modified electrode was impressive in terms of the least charge transfer resistance (Rct), highest values for diffusion coefficient (DEP) and standard heterogeneous electron transfer rate constant (k°). Analytical characterization of the modified electrode exhibited two linear dynamic ranges from 1.0×10(-7) to 1.0×10(-6)M and 1.0×10(-6) to 1.0×10(-4)M with a detection limit of (4.5±0.18)×10(-8)M. A 100-fold excess of serotonin, acetaminophen, folic acid, uric acid, tryptophan, tyrosine and cysteine, 10-fold excess of ascorbic acid and twofold excess of dopamine do not interfere in the quantification of EP at this electrode. The analytical applications of the modified electrode were demonstrated by determining EP in spiked blood serum and adrenaline tartrate injection. The modified electrode involves a simple fabrication procedure, minimum usage of the modifier, quick response, excellent stability, reproducibility and anti-fouling effects.

Multi-walled carbon nanotube/poly(glycine) modified carbon paste electrode for the determination of dopamine in biological fluids and pharmaceuticals.

A modified carbon paste electrode (CPE) for the selective detection of dopamine (DA) in presence of large excess of ascorbic acid (AA) and uric acid (UA) at physiological pH has been fabricated by bulk modification of CPE with multi-walled carbon nanotubes (MWCNTs) followed by electropolymerization of glycine (Gly). The surface morphology is compared using SEM images. The presence of nitrogen was confirmed by the energy dispersion X-ray spectroscopy (EDS) indicating the polymerization of Gly on the surface of the modified electrode. The impedance study indicates a better charge transfer kinetics for DA at CPE modified with MWCNT/polyglycine electrode. The presence of MWCNTs in carbon paste matrix triggers the extent of electropolymerization of Gly and imparts more selectivity towards DA by electrochemically not sensing AA below a concentration of 3.1×10(-4)M. Due to the exclusion of the signal for AA, the interference of AA in the determination of DA is totally ruled out by DPV method which is used for its detection at lower concentrations. Large peak separation, good sensitivity, reproducibility and stability allow this modified electrode to analyze DA individually and simultaneously along with AA and UA. Detection limit of DA was determined from differential pulse voltammetric (DPV) study and found to be 1.2×10(-8)M with a linear dynamic range of 5.0×10(-7)M to 4.0×10(-5)M. The practical analytical application of this electrode was demonstrated by measurement of DA content in dopamine hydrochloride injection and human blood serum.

Multi-walled carbon nanotube modified carbon paste electrode as an electrochemical sensor for the determination of epinephrine in the presence of ascorbic acid and uric acid.

A biocompatible electrochemical sensor for selective detection of epinephrine (EP) in the presence of 1000-fold excess of ascorbic acid (AA) and uric acid (UA) was fabricated by modifying the carbon paste electrode (CPE) with multi-walled carbon nanotubes (MWCNTs) using a casting method. The electro-catalytic activity of the modified electrode for the oxidation of EP was investigated. The current sensitivity of EP was enhanced to about five times upon modification. A very minimum amount of modifier was used for modification. The voltammetric response of EP was well resolved from the responses of AA and UA. The electrochemical impedance spectroscopic (EIS) studies reveal the least charge transfer resistance for the modified electrode. The AA peak that is completely resolved from that of EP at higher concentrations of AA and the inability of the sensor to give an electrochemical response for AA below a concentration of 3.0×10(-4)M makes it a unique electrochemical sensor for the detection of EP which is 100% free from the interference of AA. Two linear dynamic ranges of 1.0×10(-4)-1.0×10(-5) and 1.0×10(-5)-5.0×10(-7)M with a detection limit of 2.9×10(-8)M were observed for EP at modified electrode. The practical utility of this modified electrode was demonstrated by detecting EP in spiked human blood serum and EP injection. The modified electrode is highly reproducible and stable with anti fouling effects.

Sol-gel synthesis of tantalum oxide and phosphonic acid-modified carbon nanotubes composite coatings on titanium surfaces.

Carbon nanotubes used as fillers in composite materials are more and more appreciated for the outstanding range of accessible properties and functionalities they generate in numerous domains of nanotechnologies. In the framework of biological and medical sciences, and particularly for orthopedic applications and devices (prostheses, implants, surgical instruments, …), titanium substrates covered by tantalum oxide/carbon nanotube composite coatings have proved to constitute interesting and successful platforms for the conception of solid and biocompatible biomaterials inducing the osseous regeneration processes (hydroxyapatite growth, osteoblasts attachment). This paper describes an original strategy for the conception of resistant and homogeneous tantalum oxide/carbon nanotubes layers on titanium through the introduction of carbon nanotubes functionalized by phosphonic acid moieties (-P(=O)(OH)2). Strong covalent C-P bonds are specifically inserted on their external sidewalls with a ratio of two phosphonic groups per anchoring point. Experimental results highlight the stronger "tantalum capture agent" effect of phosphonic-modified nanotubes during the sol-gel formation process of the deposits compared to nanotubes bearing oxidized functions (-OH, -C=O, -C(=O)OH). Particular attention is also paid to the relative impact of the rate of functionalization and the dispersion degree of the carbon nanotubes in the coatings, as well as their wrapping level by the tantalum oxide matrix material. The resulting effect on the in vitro growth of hydroxyapatite is also evaluated to confirm the primary osseous bioactivity of those materials. Chemical, structural and morphological features of the different composite deposits described herein are assessed by X-ray photoelectron spectroscopy (XPS), scanning (SEM) and transmission (TEM) electronic microscopies, energy dispersive X-rays analysis (EDX) and peeling tests.

Poly(Patton and Reeder's reagent) modified carbon paste electrode for the sensitive detection of acetaminophen in biological fluid and pharmaceutical formulations.

An electrochemical sensor for sensitive detection of acetaminophen (AAP) was developed by electropolymerizing Patton and Reeder's reagent at carbon paste electrode (CPE). Modification improves the redox kinetics of AAP with increased current sensitivity. A similar modification at multiwall carbon nanotube (MWCNT) modified CPE did not result in an impressive charge transfer. Electrochemical impedance spectroscopy (EIS) of the bare and modified electrodes investigated imply a least charge transfer resistance at Patton and Reeder's reagent modified carbon paste electrode (MCPE/PR) as compared to bare CPE and MWCNT modified electrode. Differential pulse voltammetric (DPV) study at MCPE/PR electrode did not suffer any interference from its hydrolytic degradation product 4-aminophenol (4-AP) even in 1000-fold excess of its concentration and enables its detection simultaneously. A linear dynamic range of 0.7-100 µM with detection limit (S/N=3) of 0.53 µM was obtained for AAP. This modified electrode is easy to prepare, cheap, and having good reproducibility and stability. The analytical performance of the modified electrode is assessed by successfully applying it for the estimation of acetaminophen in different pharmaceutical samples and spiked biological fluid.

1-Dodecanethiol self-assembled monolayers on cobalt.

Cobalt and its alloys are used in a broad range of application fields. However, the use of this metal is especially limited by its strongly oxidizable nature. The use of alkanethiol self-assembled monolayers (SAMs) is a very efficient way to protect against such oxidation and/or to inhibit corrosion. This surface modification method has been particularly applied to oxidizable metals such as copper or nickel, yet the modification of cobalt surfaces by alkanethiol SAMs received limited attention up to now. In this work, we study the influence of parameters by which to control the self-assembly process of 1-dodecanethiol monolayers on cobalt: nature of the surface pretreatment, solvent, immersion time, and concentration. Each of these parameters has been optimized to obtain a densely packed and stable monolayer able to efficiently prevent the reoxidation of the modified cobalt substrates. The obtained monolayers were characterized by X-ray photoelectron spectroscopy (XPS), polarization modulation infrared reflection-absorption spectroscopy, and contact angle measurements. The stability of the optimized 1-dodecanethiol monolayer upon air exposure for 28 days has been confirmed by XPS.

Induction heating for surface triggering styrene polymerization on titanium modified with ATRP initiator.

Titanium and its alloys present high interests for technological applications due to their high corrosion resistance, mechanical properties and biocompatibility. In combination with these remarkable characteristics, some Ti applications require specific surface properties that can be imparted with suitable surface functionalizations of the TiO(2) oxide layer. The present work aims to study the surface-initiated ATR polymerization of styrene on titanium substrates, using grafted 11-(2-bromoisobutyrate)-undecyl-1-phosphonic acid as initiator and to compare the impact of two different heating ways on the efficiency of this polymerization: induction vs. conventional heating. The ability of the initiator to bind titanium substrates and act as an initiator for ATRP of styrene is investigated: both heating conditions led to the polymerization of styrene on modified titanium substrates. However, induction heating appeared to be much more efficient than conventional heating, leading to the formation of a thicker, much denser polystyrene layer than conventional heating after only 1h of polymerization.

Preparation of a polyacrylonitrile/multi-walled carbon nanotubes composite by surface-initiated atom transfer radical polymerization on a stainless steel wire for solid-phase microextraction.

We report on the fabrication and performances of a solid-phase microextraction (SPME) fiber based on a stainless steel wire coated with a covalently attached polyacrylonitrile (PAN)/multi-walled carbon nanotubes (MWCNTs) composite. This new coating is obtained by atom transfer radical polymerization (ATRP) of acrylonitrile mixed with MWCNTs. ATRP is initiated from 11-(2-bromo-2-methylpropionyloxy)-undecyl-phosphonic acid molecules grafted on the wire surface via the phosphonic acid group. The extraction performances of the fibers are assessed on different classes of compounds (polar, non-polar, aromatic, etc.) from water solutions by headspace extraction. The optimization of the parameters affecting the extraction efficiency of the target compounds was studied as well as the reproducibility and the repeatability of the fiber. The fibers sustain more than 200 extractions during which they remain chemically stable and maintain good performances (detection limits lower than 2 microg/l, repeatability, etc.). Considering their robustness together with their easy and inexpensive fabrication, these fibers could constitute promising alternatives to existing products.

Bilayers coating on titanium surface: the impact on the hydroxyapatite initiation.

Most of the actual orthopaedic devices, widely made of titanium and its alloys, present different weaknesses like ions release and risks of loosening over a long period. To solve such problems, new developments in surface modification are crucial. This work is an extension of our recent effort on the development and improvement of a multifunctional inorganic/organic bilayers coating. A thin tantalum oxide layer is formed by sol-gel synthesis followed by the modification with organophosphonic acids of the tantalum oxide layer. We focus in particular on the effect of the bilayers coating on corrosion resistance and hydroxyapatite growth rate by immersion in a simulated body fluid solution. It is also highlighted that the structure of the organophosphonic acid is of major importance on the osteoinduction character of the material.

Surface-initiated ATRP of PMMA, PS and diblock PS-b-PMMA copolymers from stainless steel modified by 11-(2-bromoisobutyrate)-undecyl-1-phosphonic acid.

A new ATRP initiator, 11-(2-bromoisobutyrate)-undecyl-1-phosphonic acid, has been synthesized and grafted as a film on a mechanically polished stainless steel (ASI304) substrate. Molecular integrity of the grafted initiator in the film, alkyl chain ordering, wettability were determined by X-ray photoelectron spectroscopy, infrared, and water contact angles. Polystyrene, poly(methyl methacrylate) and diblock copolymer (polystyrene-b-poly(methyl methacrylate)) brushes have been grafted from the flat stainless steel surfaces through surface-initiated atom transfer radical polymerization (ATRP) and characterized to check the effectiveness of the new initiator for future uses in surface-initiated ATRP.

New semifluorinated dithiols self-assembled monolayers on a copper platform.

New alpha,omega-semifluorinated dithiols HS-(CH2)11-(CF2)n-(CH2)11-SH, called DTn, and corresponding dithioacetate molecules CH3COS-(CH2)11-(CF2)n-(CH2)11-SCOCH3, called DTAn ( n = 4, 6, 8), were synthesized and used to create self-assembled monolayers (SAMs) on both untreated copper surfaces and electrochemically reduced ones. The aim of this study is to assess the organization of the resulting SAMs, particularly the effect of the presence of two perhydrogenated segments surrounding the perfluorinated one, and the ability of these difunctional molecules to bind copper substrates by only one end per molecule. In each case, the organization of the SAM is rather poor and only DTA8 molecules seem to adopt an upright position on reduced copper. In addition, the layers have been investigated by cyclic voltammetry (CV) to assess their coverage. DT4 SAMs reveal a covering ratio higher than 99%.