Designing Nanostructured Organic-Based Material by Combining Plasma Polymerization and the Wrinkling Approach.

In this work, an innovative and versatile strategy for the fabrication of nanostructured organic thin films is established based on the wrinkling phenomenon taking place in a bilayer system constituted by a liquid plasma polymer film (PPF) and a top Al coating. By means of morphological characterization (i.e., atomic force microscopy and scanning electron microscopy), it has been demonstrated that the wrinkle dimensions (i.e., wavelength and amplitude) evolve as a function of the PPF thickness according to models established for conventional polymers. The wrinkled surfaces exhibit great stability over time as their dimension did not vary after 100 days of aging, resulting from a pinning phenomenon between the Al layer and the Si substrate, hence freezing the morphology. In a second step, the wrinkled surfaces have been employed as templates for the deposition of an additional PPF third layer, giving rise to the formation of a nanostructured organic-based surface. The chemical composition of the material can be tuned through an appropriate choice of precursor (i.e., allyl alcohol or propanethiol).

Investigating the relationship between the mechanical properties of plasma polymer-like thin films and their glass transition temperature.

This work aims at understanding the influence of the substrate temperature (Ts) on the viscoelastic properties of propanethiol plasma polymer films (PPFs). By means of state-of-the-art AFM characterization-based techniques including peak force quantitative nanomechanical mapping (PFQNM), nano dynamic mechanical analysis (nDMA) and "scratch" experiments, it has been demonstrated that the mechanical behaviour of PPFs is dramatically affected by the thermal conditions of the substrate. Indeed, the material behaves from a high viscous liquid (i.e. viscosity ∼ 106 Pa s) to a viscoelastic solid (loss modulus ∼ 1.17 GPa, storage modulus ∼ 1.61 GPa) and finally to an elastic solid (loss modulus ∼ 1.95 GPa, storage modulus ∼ 8.51 GPa) when increasing Ts from 10 to 45 °C. This behaviour is ascribed to an increase in the surface glass transition temperature of the polymeric network. The latter has been correlated with the chemical composition through the presence of unbound molecules acting as plasticizers and the cross-linking density of the layers. In a second step, this knowledge is exploited for the fabrication of a nanopattern by generating surface instabilities in the propanethiol PPF/Al bilayer system.

Enhanced plasmonic processes in amino-rich plasma polymer films for applications at the biointerface.

A new plasmonic biosensor was developed in a planar chip-based format by coupling the plasmonic properties of gold nanoparticles (Au NPs) with the mechanical and bioadhesive features of unconventional organic thin films deposited from plasma, namely primary amine-based plasma polymer films (PPFs). A self-assembled layer of spherical Au NPs, 12 nm in diameter, was electrostatically immobilized onto optically transparent silanised glass. In the next step, the Au NP layer was coated with an 18 nm polymeric thick PPF layer via the simultaneous polymerization/deposition of a cyclopropylamine (CPA) precursor performed by radio frequency discharge, both in pulsed and in continuous wave modes. The CPA PFF surface plays the dual role of an adsorbent towards negatively charged chemical species as well as an enhancer of plasmonic signals. The biosensor was tested in a proof-of-concept series of experiments of human serum albumin physisorption, and chosen as a model system for blood serum. The peculiar surface features of CPA PPF, before and after the exposure to buffered solution of fluorescein isothiocyanate-labelled human serum albumin (FITC-HSA), were investigated by a multi-technique approach, including UV-visible and X-ray photoelectron spectroscopies, atomic force microscopy, scanning electron microscopy, contact angle and surface free energy measurements. The results showed the very promising potentialities from both bioanalytical and physicochemical points of view in scrutinizing the macromolecule behavior at the biointerface.

N-Doped TiO2 Photocatalyst Coatings Synthesized by a Cold Atmospheric Plasma.

This work presents a simple, fast (20 min treatment), inexpensive, and highly efficient method for synthesizing nitrogen-doped titanium dioxide (N-TiO2) as an enhanced visible light photocatalyst. In this study, N-TiO2 coatings were fabricated by atmospheric pressure dielectric barrier discharge (DBD) at room temperature. The composition and the chemical bonds of the TiO2 and N-TiO2 coatings were characterized by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The results indicate that the nitrogen element has doped the TiO2 lattice, which was further confirmed by Raman spectroscopy and grazing incidence X-ray diffraction (GIXRD). The doping mechanism was investigated using OES to study the plasma properties under different conditions. It suggests that the NH radicals play a key role in doping TiO2. The concentration of nitrogen in the N-TiO2 coatings can be controlled by changing the concentration of NH3 in the plasma or the applied power to adjust the concentration of NH radicals in the plasma. The band gap of N-TiO2 was reduced after NH3/Ar plasma treatment from 3.25 to 3.18 eV. Consequently, the N-TiO2 coating showed enhanced photocatalytic activity under white-light-emitting-diode (LED) irradiation. The photocatalytic degradation rate for the N-TiO2 coating was about 1.4 times higher than that of the undoped TiO2 coating.

Surface Engineering of Bromine-Based Plasma Polymer Films: A Step toward High Thiol Density Containing Organic Coatings.

Nowadays, the development of synthetic methods regarding the fabrication of -SH containing organic coatings continues to attract a considerable attention. Among the potential techniques, the plasma polymerization appears as one of the most promising method but the difficulty to control the chemical composition of the layers is highly limiting. In this context, in this work, we report on an original method combining dry and wet chemistry approaches in view of selectively incorporating -SH functions in organic coatings. Our strategy is based on the (i) synthesis of a bromine-containing plasma polymer film, followed by (ii) a selective grafting of dithiol-based molecule on C-Br bond. Investigating the plasma polymerization process has revealed that, in our experimental window, the load of energy in the discharge has little influence on the chemical composition as well as on the cross-linking degree of the layers. This behavior is explained by considering the concomitant influence of the gas-phase reactions and the supply of energy to the growing film through ion bombardment. With regard to the functionalization strategy, based on comparative X-ray photoelectron spectroscopy measurements, it has been unambiguously demonstrated that a selective reaction between propanedithiol and the C-Br bond acting as the reactive center takes place resulting in the removing of the bromine atom and the incorporation of -SH groups in the PPF. Depending on the grafting reaction duration, the relative proportion of carbon bearing the -SH group is found to evolve from 4 to 6%. On the other hand, the dissolution of unbounded bromine-based species in the liquid medium during the grafting procedure is also evidenced. The whole set of our results clearly demonstrates the attractiveness of our strategy paving the way for new development in the fabrication of -SH-rich-containing organic thin films.

Free-Radical-Induced Grafting from Plasma Polymer Surfaces.

With the advances in science and engineering in the second part of the 20th century, emerging plasma-based technologies continuously find increasing applications in the domain of polymer chemistry, among others. Plasma technologies are predominantly used in two different ways: for the treatment of polymer substrates by a reactive or inert gas aiming at a specific surface functionalization or for the synthesis of a plasma polymer with a unique set of properties from an organic or mixed organic-inorganic precursor. Plasma polymer films (PPFs), often deposited by plasma-enhanced chemical vapor deposition (PECVD), currently attract a great deal of attention. Such films are widely used in various fields for the coating of solid substrates, including membranes, semiconductors, metals, textiles, and polymers, because of a combination of interesting properties such as excellent adhesion, highly cross-linked structures, and the possibility of tuning properties by simply varying the precursor and/or the synthesis parameters. Among the many appealing features of plasma-synthesized and -treated polymers, a highly reactive surface, rich in free radicals arising from deposition/treatment specifics, offers a particular advantage. When handled carefully, these reactive free radicals open doors to the controllable surface functionalization of materials without affecting their bulk properties. The goal of this review is to illustrate the increasing application of plasma-based technologies for tuning the surface properties of polymers, principally through free-radical chemistry.

Near interface ionic transport in oxygen vacancy stabilized cubic zirconium oxide thin films.

The cubic phase of pure zirconia (ZrO2) is stabilized in dense thin films through a controlled introduction of oxygen vacancies (O defects) by cold-plasma-based sputtering deposition. Here, we show that the cubic crystals present at the film/substrate interface near-region exhibit fast ionic transport, which is superior to what is obtained with similar yttrium-stabilized cubic zirconia thin films.

Controlling the Formation of Nanocavities in Kirkendall Nanoobjects through Sequential Thermal Ex Situ Oxidation and In Situ Reduction Reactions.

Controlling the porosity, the shape, and the morphology of Kirkendall hollow nanostructures is the key factor to tune the properties of these tailor-made nanomaterials which allow in turn broadening their applications. It is shown that by applying a continuous oxidation to copper nanowires following a temperature ramp protocol, one can synthesize cuprous oxide nanotubes containing periodic copper nanoparticles. A further oxidation of such nanoobjects allows obtaining cupric oxide nanotubes with a bamboo-like structure. On the other hand, by applying a sequential oxidation and reduction reactions to copper nanowires, one can synthesize hollow nanoobjects with complex shapes and morphologies that cannot be obtained using the Kirkendall effect alone, such as necklace-like cuprous oxide nanotubes, periodic solid copper nanoparticles or hollow cuprous oxide nanospheres interconnected with single crystal cuprous oxide nanorods, and aligned and periodic hollow nanospheres embedded in a cuprous oxide nanotube. The strategy demonstrated in this study opens new avenues for the engineering of hollow nanostructures with potential applications in gas sensing, catalysis, and energy storage.

Simple method for gas temperature determination in CO2-containing discharges.

A simple gas temperature determination method based on the line ratio between two rotational peaks from the CO Angstrom rotational emission band is reported. A formula based on CO spectral synthesis provides a way for temperature control in plasmas containing CO molecules. This approach is validated in a CO2 flowing gas surfaguide microwave discharge operating at 2.45 GHz. The gas temperature results are compared with the ones obtained using a Boltzmann plot approach, as well as using direct comparison of measured and calculated rotational spectra of the same rotational band.

Modification of the adhesive properties of silicone-based coatings by block copolymers.

The improvement of the (bio)adhesive properties of elastomeric polydimethylsiloxane (PDMS) coatings is reported. This is achieved by a surface modification consisting of the incorporation of block copolymers containing a PDMS block and a poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) block in a PDMS matrix, followed by matrix cross-linking and immersion of the obtained materials in water. Contact angle measurements (CA), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) showed the presence of the PDMAEMA block at the surface, drastic morphology changes, and improved adhesion properties after immersion in water. Finally, underwater bioadhesion tests show that mussels adhere only to block copolymer-filled coatings and after immersion in water, i.e., when the PDMAEMA blocks have been brought to the coating surface. These observations highlight the significant role of hydrophilic groups in the surface modification of silicone coatings.

Tailoring Oxygen Reduction Reaction Kinetics of Fe-N-C Catalyst via Spin Manipulation for Efficient Zinc-Air Batteries.

The interaction between oxygen species and metal sites of various orbitals exhibits intimate correlation with the oxygen reduction reaction (ORR) kinetics. Herein, a new approach for boosting the inherent ORR activity of atomically dispersed Fe-N-C matrix is represented by implanting Fe atomic clusters nearby. The as-prepared catalyst delivers excellent ORR activity with half-wave potentials of 0.78 and 0.90 V in acidic and alkaline solutions, respectively. The decent ORR activity can also be validated from the high-performance rechargeable Zn-air battery. The experiments and density functional theory calculations reveal that the electron spin-state of monodispersed Fe active sites is transferred from the low spin (LS, t2g 6 eg 0) to the medium spin (MS, t2g 5 eg 1) due to the involvement of Fe atomic clusters, leading to the spin electron filling in σ∗ orbit, by which it favors OH- desorption and in turn boosts the reaction kinetics of the rate-determining step. This work paves a solid way for rational design of high-performance Fe-based single atom catalysts through spin manipulation.

Highly ordered hollow oxide nanostructures: the Kirkendall effect at the nanoscale.

Highly ordered ultra-long oxide nanotubes are fabricated by a simple two-step strategy involving the growth of copper nanowires on nanopatterned template substrates by magnetron sputtering, followed by thermal annealing in air. The formation of such tubular nanostructures is explained according to the nanoscale Kirkendall effect. The concept of this new fabrication route is also extendable to create periodic zero-dimensional hollow nanostructures.

Establishment of a derivatization method to quantify thiol function in sulfur-containing plasma polymer films.

Thiol-supported surfaces draw more and more interest in numerous fields of applications from biotechnology to catalysis. Among the various strategies to generate such surfaces, the plasma polymerization of a thiol-containing molecule appears to be one of the ideal candidates. Nevertheless, considering such an approach, a careful characterization of the material surface chemistry is necessary. In this work, an original chemical derivatization method aiming to quantitatively probe the -SH functions in plasma polymers was established using N-ethylmaleimide as a labeling molecule. The method was qualitatively and quantitatively validated on self-assembled monolayers of 3-mercaptopropyltrimethoxysilane exhibiting a -SH-terminated group used as "model" surface. For a quantitative determination of the -SH content in propanethiol plasma polymers, the kinetics of the reaction was investigated. The latter is described as a two-step mechanism, namely a fast surface reaction followed by a diffusion-limited one. The density of -SH groups deduced from the derivatization method (~4%) is in good agreement with typical values measured in some other plasma polymer families. The whole set of our data opens up new possibilities for optimizing the -SH content in thiol-based plasma polymer films.

Combining physical vapor deposition structuration with dealloying for the creation of a highly efficient SERS platform.

Nanostructured noble metal thin films are highly studied for their interesting plasmonic properties. The latter can be effectively used for the detection of small and highly diluted molecules by the surface-enhanced Raman scattering (SERS) effect. Regardless of impressive detection limits achieved, synthesis complexity and the high cost of gold restrict its use in devices. Here, we report on a novel two-step approach that combines the deposition of a silver-aluminum thin film with dealloying to design and fabricate efficient SERS platforms. The magnetron sputtering technique was used for the deposition of the alloy thin film to be dealloyed. After dealloying, the resulting silver nanoporous structures revealed two degrees of porosity: macroporosity, associated to the initial alloy morphology, and nanoporosity, related to the dealloying step. The resulting nanoporous columnar structure was finely optimized by tuning deposition (i.e., the alloy chemical composition) and dealloying (i.e., dealloying media) parameters to reach the best SERS properties. These are reported for samples dealloyed in HCl and with 30 atom % of silver at the initial state with a detection limit down to 10-10 mol·L-1 for a solution of rhodamine B.

Innovative One-Shot Paradigm to Tune Filler-Polymer Matrix Interface Properties by Plasma Polymer Coating in Osteosynthesis Applications.

The present study aims to improve the interfacial bonding between hydroxyapatite particles (HAs) and polylactide (PLA) to enhance the mechanical performance and biocompatibility of bone implants based on HA/PLA. For this, one-shot surface functionalization of HA via plasma polymerization is developed. Taking advantage of acetylene plasma chemistry, the hydrophobicity of HA particles was finely tuned prior to their introduction into a PLA matrix via an extrusion process. The effect of the plasma power (20 or 100 W) on the composition of the plasma polymer film (PPF) formed on the HA surface was studied via Fourier transform infrared (FTIR) spectroscopy, time-of-flight secondary-ion mass spectrometry (ToF-SIMS), and X-ray photoelectron spectroscopy (XPS). The amount of PPF formed was evaluated via thermogravimetric analyses (TGA). Cytotoxicity of the modified HA particles was monitored by the WST-1 proliferation assay and lactate dehydrogenase (LDH) release and showed that independent on the studied conditions, cell viability remained above the 70% threshold and LDH accumulation changes were insignificant, suggesting good biocompatibility. Contact angle measurements and morphological and rheological analyses showed that the low working power promoted more hydrophobic surfaces and a better HA/PLA interface. Dynamic mechanical analyses revealed that the storage modulus at 37 °C increased for the composite containing functionalized particles by 1.5 times compared to the neat particle's composites. This work opens a route toward further one-shot development of improved scaffolds for bone tissue engineering.

Recent Advances in the Development of Nano-Sculpted Films by Magnetron Sputtering for Energy-Related Applications.

In this paper, we overview the recent progress we made in the magnetron sputtering-based developments of nano-sculpted thin films intended for energy-related applications such as energy conversion. This paper summarizes our recent experimental work often supported by simulation and theoretical results. Specifically, the development of a new generation of nano-sculpted photo-anodes based on TiO2 for application in dye-sensitized solar cells is discussed.

Mechanical and microstructural properties of hybrid poly(ethylene glycol)-soy protein hydrogels for wound dressing applications.

Biomimetic hydrogel made of poly(ethylene glycol) and soy protein with a water content of 96% has been developed for moist wound dressing applications. In this study, such hybrid hydrogels were investigated by both tensile and unconfined compression measurements in order to understand the relationships between structural parameters of the network, its mechanical properties and protein absorption in vitro. Elastic moduli were found to vary from 1 to 17 kPa depending on the composition, while the Poisson's ratio (approximately 0.18) and deformation at break (approximately 300%) showed no dependence on this parameter. Further calculations yielded the crosslinking concentration, the average molecular weight between crosslinks (M(C)) and the mesh size. The results show that reactions between PEG and protein create polymeric chains comprising molecules of PEG and protein fragments between crosslinks. M(C) is three times higher than that expected for a "theoretical network." On the basis of this data, we propose a model for the 3D network of the hydrogel, which is found to be useful for understanding drug release properties and biomedical potential of the studied material.

Spectroscopic observation of oxygen dissociation on nitrogen-doped graphene.

Carbon nanomaterials' reactivity towards oxygen is very poor, limiting their potential applications. However, nitrogen doping is an established way to introduce active sites that facilitate interaction with gases. This boosts the materials' reactivity for bio-/gas sensing and enhances their catalytic performance for the oxygen reduction reaction. Despite this interest, the role of differently bonded nitrogen dopants in the interaction with oxygen is obscured by experimental challenges and has so far resisted clear conclusions. We study the interaction of molecular oxygen with graphene doped via nitrogen plasma by in situ high-resolution synchrotron techniques, supported by density functional theory core level simulations. The interaction leads to oxygen dissociation and the formation of carbon-oxygen single bonds on graphene, along with a band gap opening and a rounding of the Dirac cone. The change of the N 1 s core level signal indicates that graphitic nitrogen is involved in the observed mechanism: the adsorbed oxygen molecule is dissociated and the two O atoms chemisorb with epoxy bonds to the nearest carbon neighbours of the graphitic nitrogen. Our findings help resolve existing controversies and offer compelling new evidence of the ORR pathway.

Fluorination of vertically aligned carbon nanotubes: from CF4 plasma chemistry to surface functionalization.

The surface chemistry of plasma fluorinated vertically aligned carbon nanotubes (vCNT) is correlated to the CF4 plasma chemical composition. The results obtained via FTIR and mass spectrometry are combined with the XPS and Raman analysis of the sample surface showing the dependence on different plasma parameters (power, time and distance from the plasma region) on the resulting fluorination. Photoemission and absorption spectroscopies are used to investigate the evolution of the electronic properties as a function of the fluorine content at the vCNT surface. The samples suffer a limited ageing effect, with a small loss of fluorine functionalities after two weeks in ambient conditions.

Surface tailoring of polyacrylate-grafted graphene oxide for controlled interactions at the biointerface.

The actual surface termination and lateral size of a nanomaterial is crucial in its interaction with biomolecules at the aqueous interface. Graphene oxide (GO) nanosheets have been demonstrated as promising nanoplatform for both diagnostic and therapeutic applications. To this respect, 'smart' GO nanocarriers have been obtained by the surface functionalisation with polymers sensitive, e.g., to pH, as the polyacrylate (PAA) case. In this work, hybrid GO/PAA samples prepared respectively at low (GOPAAthin) or high (GOPAAthick) monomer grafting ratio, were scrutinised both theoretically, by molecular dynamic calculations, and experimentally by a multitechnique approach, including spectroscopic (UV-visible, fluorescence, Raman, Attenuated-total reflectance-Fourier transformed infrared and X-ray photoelectron spectroscopies), spectrometric (time-of-flight secondary ion and electrospray ionisation mass spectrometries) and microscopic (atomic force and confocal microscopies) methods. The actual surface termination, evaluated in terms of the relative ratio between polar and dispersive groups at the surface of the GO/polymer systems, was found to correlate with the average orientation of hydrophilic/hydrophobic domains of albumin, used as model protein. Moreover, the comparison among GO, GO-PAAthin and GO-PAAthick in the optical response at the interface with aqueous solutions, both at acid and at physiological pH, showed that the hybrid GO-polymer platform could be suitable not only to exploit a pH-triggered drug release but also for a modulation of the GO intrinsic emission properties. Energy transfer experiments on the GO/polymer oxide/fluorescein-labelled albumin/doxorubicin assembly showed significant differences for GO and GO-PAA samples, thus demonstrating the occurrence of different electronic processes at the hybrid nano-bio-interfaces. Confocal microscopy studies of cellular uptake in neuroblastoma cells confirmed the promising potentialities of the developed nanoplatform for applications at the biointerface.