Grafting of 4-pyrrolyphenyldiazonium in situ generated on NiTi, an adhesion promoter for pyrrole electropolymerisation?

Electrografting of 4-Nitrobenzenediazonium Salts on Al-7075 Alloy Surfaces-The Role of Intermetallic Particles

In this work, the electrografting of Al-7075 aluminium alloy substrates with 4-nitrobenzenediazonium salt (4-NBD) films was studied on a complex aluminium alloy surface. Prior to the electrografting reaction, the substrates were submitted to different surface treatments to modify the native aluminium oxide layer and unveil intermetallic particles (IMPs). The formation of the 4-NBD films could be correlated with the passive film state and the distribution of IMPs. The corresponding electrografting reaction was performed by cyclic voltammetry which allowed the simultaneous analysis of the redox reaction by a number of complementary surface-analytical techniques. Spatially resolved thin film analysis was performed by means of SEM-EDX, AFM, PM-IRRAS, Raman spectroscopy, XPS, and SKPFM. The collected data show that the 4-NBD film is preferentially formed either on the Al oxide layer or the IMP surface depending on the applied potential range. Potentials between -0.1 and -1.0 VAg/AgCl mostly generated nitrophenylene films on the oxide covered aluminium, while grafting between -0.1 and -0.4 VAg/AgCl favours the growth of these films on IMPs.

Improving the abrasion resistance of Ti6Al4V alloy by modifying its surface with a diazonium salt and attaching of polyurethane

Commonly used endoprostheses in the orthopedic industry are those made of Ti6Al4V titanium alloy. Unfortunately, this material has low abrasion resistance, and therefore methods of their modification are still sought. A sensible approach is coating the alloy with a layer of a polymer having higher abrasion resistance. The adhesion of polymers to alloy is low, therefore the alloy requires prior modification. In this work, the alloy was modified with three types of diazonium salt and the influence of substituent on the effectiveness of modification was determined. Then, five or ten polyurethane layers were attached to the surface of the modified alloy. Using Raman mapping, the uniform distribution of layers was proved. Layers are stable in simulated human body fluids. The effectiveness of attaching subsequent layers of polyurethane was also confirmed by nanoindentation. The main focus of this work was to improve the wear resistance of the titanium alloy. The obtained results indicate that the titanium alloy with a polyurethane layer has almost ten times lower coefficient of friction compared to pure alloy. Such a low value has not been described in the literature so far. These results are the first step for obtaining endoprostheses with very high abrasion resistance.

Surface Characterization of Electro-Assisted Titanium Implants: A Multi-Technique Approach

The understanding of chemical-physical, morphological, and mechanical properties of polymer coatings is a crucial preliminary step for further biological evaluation of the processes occurring on the coatings' surface. Several studies have demonstrated how surface properties play a key role in the interactions between biomolecules (e.g., proteins, cells, extracellular matrix, and biological fluids) and titanium, such as chemical composition (investigated by means of XPS, TOF-SIMS, and ATR-FTIR), morphology (SEM-EDX), roughness (AFM), thickness (Ellipsometry), wettability (CA), solution-surface interactions (QCM-D), and mechanical features (hardness, elastic modulus, adhesion, and fatigue strength). In this review, we report an overview of the main analytical and mechanical methods commonly used to characterize polymer-based coatings deposited on titanium implants by electro-assisted techniques. A description of the relevance and shortcomings of each technique is described, in order to provide suitable information for the design and characterization of advanced coatings or for the optimization of the existing ones.

Diazonium Salts: Versatile Molecular Glues for Sticking Conductive Polymers to Flexible Electrodes

Adhesion of polymers to surfaces is of the upmost importance in timely applications such as protective coatings, biomaterials, sensors, new power sources and soft electronics. In this context, this work examines the role of molecular interactions in the adhesion of polypyrrole thin films to flexible Indium Tin Oxide (ITO) electrodes grafted with aryl layers from various diazonium salts, namely 4-carboxybenzenediazonium (ITO-CO2H), 4-sulfonicbenzenediazonium (ITO-SO3H), 4-N,N-dimethylbenzenediazonium (ITO-N(CH3)2), 4-aminobenzenediazonium (ITO-NH2), 4-cyanobenzenediazonium (ITO-CN) and 4-N-phenylbenzenediazonium (ITO-NHPh). It was demonstrated that PPy thin layers were adherent to all aryl-modified surfaces, whereas adhesive failure was noted for bare ITO following simple solvent washing or sonication. Adhesion of polypyrrole was investigated in terms of hydrophilic/hydrophobic character of the underlying aryl layer as probed by contact angle measurements. It was found that sulfonic acid-doped polypyrrole (PPy-BSA) thin films were preferably deposited on the most hydrophobic surfaces. More importantly, the redox properties and electrochemical impedance of PPy were closely related to the hydrophobic character of the aryl layers. This work demonstrates that diazonium compounds are unique molecular glues for conductive polymers and permit to tune their interfacial properties. With robust, diazonium-based architectured interfaces, one can design high performance materials for e.g., sensors, printed soft electronics and flexible thermoelectrics.

Tracking metal ions with polypyrrole thin films adhesively bonded to diazonium-modified flexible ITO electrodes

Adhesively bonded polypyrrole thin films doped with benzene sulfonic acid (BSA) were electrodeposited on aminobenzenediazonium-modified flexible ITO electrodes and further employed for the detection of Pb²⁺, Cu²⁺, and Cd²⁺ metal ions in aqueous medium. The aminophenyl (AP) adhesive layer was grafted to ITO by electroreduction of the in situ generated parent diazonium compound. Polypyrrole (PPy) thin films exhibited remarkable adhesion to aminophenyl (ITO-AP). The strongly adherent polypyrrole films exhibited excellent electroactivity in the doped state with BSA which itself served to chelate the metal ions in aqueous medium. The surface of the resulting, modified flexible electrode was characterized by XPS, SEM, and electrochemical methods. The ITO-AP-PPy electrodes were then used for the simultaneous detection of Cu²⁺, Cd²⁺, and Pb²⁺ by differential pulse voltammetry (DPV). The detection limits were 11.1, 8.95, and 0.99 nM for Cu²⁺, Cd²⁺, and Pb²⁺, respectively. In addition, the modified electrodes displayed a good reproducibility, making them suitable for the determination of heavy metals in real wastewater samples.

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.