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Poly tetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF) polymer surfaces were exposed to a remote N 2 or O 2 r.f. plasma. The effect of the plasma power and treatment time on the surface energy and the surface composition were studied by static water contact angle (WCA) and X-ray photoelectron spectroscopy (XPS). In every case, a strong defluorination of the surface was observed. Except for PTFE treated by oxygen, all the surfaces became more hydrophilic after plasma treatment, owing to the grafting of polar nitrogen or oxygen functions. The kinetics of defluorination and grafting seems to be favoured for PVDF and PVF surfaces.

International audienceSurface functionalization with ultrathin layers exhibiting a highly robust interface is of paramount importance for designing materials with tailored properties or operating functions, without modifying drastically the material’s bulk structures. A fine-tuning of the surface composition obtained, for instance from binary mixed layers, is also a key issue for developing high value-added applications like efficient sensors. Herein, binary mixtures of calix[4]arene-tetra-diazonium salts generated in situ from their corresponding calix[4]tetra-anilines are electrografted to form covalently bound monolayers onto substrates for yielding versatile functionalizable molecular platforms. Wettability studies, X-ray photoelectron spectroscopy analyses, and scanning electrochemical microscopy show the formation of homogeneous mixed monolayers. The distribution of the two calixarenes on the surface is directed by their relative molar fraction in the deposition solution. The strategy allows the control of the composition of mixed monolayers in a one-step approach. Postfunctionalization of the mixed layers with ferrocene centers is performed to exemplify the benefit of a dilution procedure when functional groups are introduced at the calix[4]arene small rim. This study highlights the potential of diazonium salt electrografting as a competitive alternative to chemisorption strategies such as self-assembled monolayers of alkyl thiols in the field of surface functionalization

DNA microarray assay performance is commonly compromised by spot-spot probe and signal variations as well as heterogeneity within printed microspots. Accurate metrics for captured DNA target signal rely upon uniform spot distribution of both probe and target DNA to yield reliable hybridized signal. While often presumed, this is neither easily achieved nor often proven experimentally. High resolution imaging techniques were used to determine spot heterogeneity in identical DNA array microspots comprising varied ratios of unlabeled and dye-labeled DNA probes contact printed onto commercial arraying surfaces. Epifluorescence imaging data for individual array microspots were correlated with time-of-flight secondary ion mass spectrometry (TOF-SIMS) chemical state imaging of the same spots. Epifluorescence imaging intensity distinguished varying DNA density distributed both within a given spot and from spot-to-spot. TOF-SIMS chemical analysis confirmed these heterogeneous printed DNA distributions by tracking bound Cy3 dye-, DNA base, and phosphate- specific ion fragments often correlating to fluorescence patterns within identical spots. TOF-SIMS ion fragments originating from probe DNA and Cy3 dye are enriched in microspot centers, correlating with high fluorescence intensity regions. Both TOF-SIMS and epifluorescence supports Marangoni flow effects on spot drying, with high density DNA-Cy3 located in spot centers and non-homogeneous DNA distribution within printed spots. Microspot image dimensional analysis results for DNA droplet spreading show differing DNA densities across printed spots. The study directly supports different DNA probe chemical and spatial microenvironments within spots that yield spot-spot signal variations known to affect DNA target hybridization efficiencies and kinetics. These variations critically affect probe-target duplex formation and DNA array signal generation.

A comparative study of polytetrafluoroethylene (PTFE) surfaces treated by the post-discharge of He and He-O2 plasmas at atmospheric pressure is presented. The characterization of treated PTFE surfaces and the species involved in the surface modification are related. In pure He plasmas, no significant change of the surface has been observed by X-ray photoelectron spectroscopy (XPS), dynamic water contact angles (dWCA) and atomic force microscopy (AFM), in spite of important mass losses recorded. According to these observations, a layer-by-layer physical etching without any preferential orientation is proposed, where the highly energetic helium metastables are the main species responsible for the scission of −(CF2)n− chains. In He−O2 plasmas, as the density of helium metastables decreases as a function of the oxygen flow rate, the treatment leads to fewer species ejected from the PTFE surfaces (in agreement with mass loss measurements and the detection of fluorinated species onto aluminum foil). However, the dWCA and AFM measurements show an increase in the hydrophobicity and the roughness of the surface. The observed alveolar structures are assumed to be caused by an anisotropic etching where the oxygen atoms etch mainly the amorphous phase.

PTFE samples were treated by low-pressure, O RF plasmas. The adsorption of BSA was used as a probe for the protein resistant properties. The exposure of PTFE to an O plasma leads to an increase in the chamber pressure. OES reveals the presence of CO, CO and F in the gas phase, indicating a strong etching of the PTFE surface by the O plasma. Furthermore, the high resolution C1s spectrum shows the appearance of CF, CF and C-CF components in addition to the CF component, which is consistent with etching of the PTFE surface. WCA as high as 160° were observed, indicating a superhydrophobic behaviour. AFM Images of surfaces treated at high plasma power showed a increase in roughness. Lower amounts of BSA adsorption were detected on high power, O plasma-modified PTFE samples compared to low power, oxygen plasma-modified ones.

PTFE surfaces have been exposed to neutral atoms and molecules, and to electrons originating from a modified RF nitrogen plasma, able to filter out the cations. The changes in surface energy of the modified polymer, determined by the water contact angle, are linearly related to the increase of the nitrogen concentration at the surface, determined by XPS. The deconvolution of the spectral envelope of the C 1s photoelectron peak shows a strong modification of the nature of the chemical groups on the surface, depending on the treatment time and on the plasma power. Electrons are postulated to be mainly responsible for the appearance of the CF 3 group, while the major functions induced by nitrogen seem to be C N, C-N and a possible F-C-N group.