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It is accepted that the macroscopic properties of functional plasma polymer films (PPF) are defined by their functional density and their crosslinking degree ( χ ) which are quantities that most of the time behave in opposite trends. If the PPF chemistry is relatively easy to evaluate, it is much more challenging for χ . This paper reviews the recent work developed in our group on the application of principal component analysis (PCA) to time-of-flight secondary ion mass spectrometric (ToF-SIMS) positive spectra data in order to extract the relative cross-linking degree ( χ ) of PPF. NH 2 -, COOR- and SH-containing PPF synthesized in our group by plasma enhanced chemical vapor deposition (PECVD) varying the applied radiofrequency power ( P RF ), have been used as model surfaces. For the three plasma polymer families, the scores of the first computed principal component (PC1) highlighted significant differences in the chemical composition supported by X-Ray photoelectron spectroscopy (XPS) data. The most important fragments contributing to PC1 (loadings > 90%) were used to compute an average C/H ratio index for samples synthesized at low and high P RF . This ratio being an evaluation of χ , these data, accordingly to the literature, indicates an increase of χ with P RF excepted for the SH-PPF. These results have been cross-checked by the evaluation of functional properties of the plasma polymers namely a linear correlation with the stability of NH 2 -PPF in ethanol and a correlation with the mechanical properties of the COOR-PPF. For the SH-PPF family, the peculiar evolution of χ is supported by the understanding of the growth mechanism of the PPF from plasma diagnostic. The whole set of data clearly demonstrates the potential of the PCA method for extracting information on the microstructure of plasma polymers from ToF-SIMS measurements. [ABSTRACT FROM AUTHOR]

In this work, we report on the synthesis of ethyl lactate-based plasma polymer film (ELPPF) by plasma enhanced chemical vapour deposition (PECVD). Using a design of experiments, it appears that, among other, the injected power ( PRF) is the key parameter affecting the ELPPF features. Indeed, we observe a strong decrease of the COO-C/H functionalities (from 12 to 2 at.%) within a limited PRF domain. A more precise analysis of the film chemistry by combining XPS and chemical derivatization reveals that up to 95% of these carboxyl-based functions are esters. On the other hand, we show that the cross-linking degree of the ELPPF can be increased by a factor of two as a function of PRF. This work paves the way for the tailoring of the barrier properties of ELPPF by controlling the ester content and the cross-linking degree of the PPF. [ABSTRACT FROM AUTHOR]

Abstract: Superhydrophobic poly(tetrafluoro-ethylene) (PTFE) like thin films were grown on silicon wafers using a plasma-based hybrid process consisting on sputtering a carbon target in an Ar/CF4 atmosphere. The influence of the bias voltage applied to the substrate (VBias) as well as of the gas mixture composition (%CF4) on the chemical composition, the wettability and the morphology of the deposited thin films were evaluated. The chemical composition measured by X-ray Photoelectron Spectroscopy (XPS) has revealed that the F/C atomic ratio is always lower than for conventional PTFE (F/C=2) and that it decreases when VBias increases (from F/C=1 for VBias =−100V to F/C=0.75 for VBias =−200V). This behavior is associated with the preferential sputtering of the fluorine atoms during the plasma-assisted growth of the films. Consecutively, a self-nanostructuration enhanced when increasing VBias is observed. As a consequence, the water contact angle (WCA) measurements range from 70° up to 150° depending on (i) the fluorine concentration and (ii) on the magnitude of the nanostructuration. In addition, for the films presenting the highest WCAs, a small hysteresis between the advancing and receding WCAs is observed (<10°) allowing these films to fulfill completely the requirements of superhydrophobicity. The nanostructuration is probably due to the chemical etching by fluorine atoms of the fluorinated group. In order to get more understanding on the wettability mechanisms of these surfaces, the topography of the films has been evaluated by atomic force microscopy (AFM). The data have revealed, for all films, a dense and regular structure composed by conic objects (AvH is their average height and AvD is the average distance between them) for which the dimensions increase with VBias. A correlation between AvH/AvD, defined as the “morphological ratio”, with the WCA was established. Theoretical evaluations of the WCA using the Wenzel and Cassie equations with, as inputs, the features of the deposited thin film surfaces measured by AFM suggest that the wetting regime is intermediate between these two ideal situations. [Copyright &y& Elsevier]

In this work, we provide new insight on the influence of the precursor (CH4 vs. C2H2) on the mechanical properties of a-C:H coatings synthesized in a hybrid PECVD/PVD process. For a given set of plasma parameters, the films synthesized in CH4/Ar gas mixture are found harder than the ones prepared in C2H2/Ar atmosphere despite their lower sp3 density and similar hydrogen content. This unusual behavior is attributed to different molecular organization of the polymeric network constituting the films. The latter is explained considering the influence of the chemical nature of the film-forming species on the cross-linking and branching degree of the films. The whole set of our results unambiguously demonstrates that additional factors than the sp3 and hydrogen content have to be considered for explaining the mechanical properties of a-C:H layers. [ABSTRACT FROM AUTHOR]

• Ag nanoclusters- SiO 2 /Al 2 O 3 /ZrO 2 coatings were obtained on SS316L, Tigr4 and Tigr5 by co-sputtering. • All coatings have a mean roughness <0.2 µm and good mechanical adhesion to the substrate. • ZrO 2 based coatings are the most stable in wet environment. • ZrO 2 -Ag coatings can reduce S. aureus adhesion even if Ag release is negligible. • ZrO 2 -Ag coatings are promising for temporary fixation devices. Bacterial contamination and bone tissue overgrowth are currently the main issues for temporary fixation devices. The aim of this research is the development of innovative inorganic coatings able to reduce bacterial adhesion and bone tissue overgrowth without hampering cytocompatibility. 316L stainless-steel, Titanium grade4 and Titanium grade5 were selected as substrates, as currently used in temporary fixation devices. Starting from previous results on silica, alumina and zirconia were selected as coating matrices, according to their higher chemical stability, reduced bacterial adhesion and possible reduction of tissue overgrowth. Coatings were produced by co-sputtering. Coating adhesion was evaluated by tape test. Samples were immersed in ultrapure water up to 28 days to investigate silver release and chemical stability in fluids. Surface roughness was measured by contact profilometry. Surface wettability was determined by contact angle measurements and antibacterial activity was studied against antibiotic resistant S aureus. The research demonstrates the possibility to obtain coatings with roughness lower than the critical threshold for the increase of bacterial adhesion (0.2 µm) and optimal mechanical adhesion to metallic substrates. Coating chemical stability in water is strongly affected by the coating matrix composition. Silver release can be tailored to obtain antibacterial and biocompatible surfaces. [ABSTRACT FROM AUTHOR]