The study of Diels-Alder reactions in materials science is of increasing interest. The main reason for that is the potential thermoreversibility of the reaction. Aiming to predict the behavior of a ...material modified with maleimido and furyl moieties,
H NMR and UV-Vis solution studies of the Diels-Alder reaction between furfuryl alcohol and two
-hydroxymaleimides are explored in the present study. Rate constants, activation energy, entropy, and enthalpy of formation were determined from each technique for both reacting systems.
and
isomers were distinguished in
H NMR, and the transition from a kinetic, controlled Diels-Alder reaction to a thermodynamic one could be observed in the temperature range studied. A discussion on the effect of that on the application in a material was performed. The approach selected considers a simplified equilibrium of the Diels-Alder reaction as the kinetic model, allowing materials scientists to evaluate the suitability of using the reacting molecules for the creation of thermoresponsive materials. The proposed approach determines the kinetic constants without the direct influence of the equilibrium constant value, thereby allowing a more objective data analysis. The effects of the selection of kinetic model, analytical method, and data treatment are discussed.
•We examine the hydrophobic recovery of plasma treated PDMS surfaces.•We find the occurrence of singularities under nitrogen for low aging temperatures.•Theses singularities account for different ...population of relaxation processes.•The faster concerns reorientation processes at the surface of the crosslinked layer.•The slower concerns diffusion processes in the sub-surface region.
Herein, the hydrophobic recovery of argon plasma treated polydimethylsiloxane surfaces is explored. In contrast to previous works, environmental contamination is here taken into account. We find that diffusion and reorientation strongly dominate the hydrophobic recovery under high thermal activation (60°C), no matter the surrounding environment during storage. However, at lower temperature (24°C and below), we find that contamination plays a major role in lab atmosphere environment. By working at low temperature and under inert nitrogen atmosphere to slow down the diffusion and reorientation dynamics and to avoid contamination, we identify two different temperature-dependent regimes in the kinetics of the hydrophobic recovery. One is fast and involves exclusively relaxation processes occurring in the surface region. The second, much slower, concerns diffusion phenomena in the sub-surface region. Thereby, the specific impact of bulk diffusion and surface reorientation processes can be distinguished during aging by slowing down the surface dynamics and by eliminating all possible sources of contamination.
Maleic anhydride plasma polymer was deposited at the surface of carbon fibers and functionalized with vinyl and thiol groups to improve its adhesion strength with an acrylate matrix cured by an ...electron beam. A characterization of the fiber surface properties was done before and after coating (topography, surface chemistry, and surface energy). Sharp improvements of the interfacial shear strength (+ 120%), measured by a micromechanical test derived from the pull-out test, were obtained and, to the best of our knowledge, never reported before. The values were close to the ones obtained with a thermal cure. The comparison of this approach with other types of surface treatments (oxidation, grafting of coupling agents) enabled the establishment of a general strategy for the improvement of the interfacial adhesion in carbon fiber composites cured by an electron beam and potentially the improvement of their mechanical properties. This strategy is based on a high surface density of functionalities that are generating covalent bonding during the polymerization of the matrix and on the insertion of a polymer layer strongly attached to the fiber surface and acting as a buffer between the fiber surface and the matrix to counteract the generation of stress in the interphase.
In this work, the use of Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) was explored as a technique for monitoring the interfacial retro Diels–Alder (retro DA) reaction occurring on ...well-controlled self-assembled monolayers (SAMs). A molecule containing a Diels–Alder (DA) adduct was grafted on to the monolayers, then the surface was heated at different temperatures to follow the reaction conversion. A TOF-SIMS analysis of the surface allowed the detection of a fragment from the molecule, which is released from the surface when retro DA reaction occurs. Hence, by monitoring the decay of this fragment’s peak integral, the reaction conversion could be determined in function of the time and for different temperatures. The viability of this method was then discussed in comparison with the results obtained by 1H NMR spectroscopy.
Plasma polymers are micro-, or more commonly, nano-sized coatings that can be deposited on a variety of substrates through different approaches. The versatility of these polymers is incremented by ...the possibility to use other precursors than conventional polymerization reactions and by potential changes in the polymerization mechanisms according to the intrinsic physical and chemical properties of the plasma. That flexibility offers a fruitful ground to a great range of scientific and engineering fields, but it also brings many challenges for universalization of empirical observations. In this review, the use of different precursors, substrates and changes in plasma external parameters were evaluated as common, but not necessarily ideal nor exhaustive, variables for the analysis of mechanical properties of plasma polymer films. The commonly reported trends are complemented with the exceptions, and a variety of hypothesis drawn by the empirical observations are shown. The techniques and methods used for determining the mechanical properties of plasma polymers, the effect of post-treatments on them and some applications are evaluated. Finally, a general conclusion highlighting the challenges of the field is provided.
Article highlights
The mechanical properties of plasma polymers are evaluated as a function of selected parameters.
The techniques of characterization of mechanical properties of plasma polymers are summarized.
A discussion of future and current demands for the analysis of mechanical properties of plasma polymers is done.
Chemo-mechanotransduction, the way by which mechanical forces are transformed into chemical signals, plays a fundamental role in many biological processes. The first step of mechanotransduction often ...relies on exposure, under stretching, of cryptic sites buried in adhesion proteins. Likewise, here we report the first example of synthetic surfaces allowing for specific and fully reversible adhesion of proteins or cells promoted by mechanical action. Silicone sheets are first plasma treated and then functionalized by grafting sequentially under stretching poly(ethylene glycol) (PEG) chains and biotin or arginine-glycine-aspartic acid (RGD) peptides. At unstretched position, these ligands are not accessible for their receptors. Under a mechanical deformation, the surface becomes specifically interactive to streptavidin, biotin antibodies, or adherent for cells, the interactions both for proteins and cells being fully reversible by stretching/unstretching, revealing a reversible exposure process of the ligands. By varying the degree of stretching, the amount of interacting proteins can be varied continuously.
A new method is described for producing patterned solid surfaces with reactive groups. This entails pulsed plasma deposition of anhydride functionalized films, followed by the covalent attachment of ...an amine-terminated nucleophile via aminolysis reaction. Characterization of the surface chemistry was achieved by XPS, PM-IRRAS and contact angle measurement. Patterning was achieved by DUV irradiation using an ArF excimer laser and an interferometric set-up. Well-defined patterns have been obtained at different scales on a large surface area and using this unique procedure. Spectroscopic characterizations coupled with AFM measurements allow explanation to some measure of the photoinduced phenomena. Trenches with a width ranging from 75 to 500 nm and a depth up to 30 nm were written. Using this approach it is possible to create combinatorial patterned surfaces with well-controlled topography and chemistry.
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► Changes in surface composition of polydimethylsiloxane surfaces were studied after argon plasma exposition. ► Aging processes were studied in different atmospheric conditions. ► ...Free radicals are created and the nature of these radicals has been highlight. ► Silyl radicals react with allyl groups of antagonist filler-free polydimethylsiloxane resin during the crosslinking step. ► A high interfacial resistance has been observed under elongation/retraction cycles.
We propose a simple method to elaborate a filler-free stretchable PDMS surface strong enough to resist to successive elongation/retraction cycles even at high degree of stretching. It consists in creating free radicals on a filler-containing PDMS surface by argon plasma exposure and reacting them with a filler-free PDMS resin during the crosslinking step. Changes of physical and chemical properties upon plasma modification are monitored by FTIR and XPS spectroscopies, contact angle measurements and atomic force microscopy. Electron spin resonance (ESR) is used to identify the nature of radicals involved in interfacial bonding. Although a brittle silica-like layer is created on the filler-containing PDMS surface after plasma treatment, an increase in the PDMS/PDMS interfacial strength is observed and a high interfacial resistance has been found under elongation/retraction (stretching/relaxation) cycles.
The development of coating methods that enable us to combine antagonist properties on a single material is a real challenge. This active research topic can impact, for instance, the textile field to ...engineer fabrics with liquid-repellent properties on one side and superhydrophilic properties on the opposite side. In this context, we have developed an easy surface functionalization process that provides durable Janus wetting properties to fabrics. On the basis of plasma-enhanced chemical vapor deposition (PECVD), we report a simple and reproducible three-step functionalization method that led to a coating with superhydrophobic and superoleophobic properties on one side of the porous substrate and superhydrophilic properties on the opposite side. A thin, fluorinated polymer film was deposited on one side, while the other side was functionalized with a polymer coating made of maleic anhydride, subsequently hydrolyzed to provide carboxylic acid groups to the surface. Static contact angles up to 169° with water and 162° with hexadecane were obtained on the fluorinated side of the fabric thanks to an appropriate combination of surface chemistry with dual-scale surface roughness. In addition, roll-off angles of 6 and 14° with water and hexadecane, respectively, were measured on this side of the sample. As for the opposite side, the hydrolyzed plasma polymer made of maleic anhydride enables us to obtain a surface that fully absorbs water and hexadecane. In addition, these tremendous properties were durable because no significant change was observed after aging and washing cycles. This simple surface functionalization process based on plasma polymerization is an innovative solution for the fabrication of textile with durable waterproof and breathable properties. Besides, the described concept can be adapted to numerous other applications that require Janus properties to porous substrates.
Plasma polymerization has gained increasing attention in surface functionalization. We use here chemical force titration to characterize PDMS (polydimethylsiloxane) substrates modified by maleic ...anhydride-pulsed plasma polymerization. The coating is hydrolyzed to promote the formation of dicarboxylic acid groups. To enhance the variation of the adhesion forces as a function of pH, we use AFM tips modified in the same way as the substrates. The pH-dependent adhesion measurements are performed at different KCl concentrations. The dicarboxylic nature of the maleic acid groups clearly emerges from the force titration curves. The surface pK a values (pK a 1 = 3.5 ± 0.5 and pK a 2 = 9.5 ± 0.5) of the dicarboxylic acids are evaluated from low electrolyte concentration solutions. The values are shifted toward higher pK a values when compared to maleic acid in solution. The first pK a appears in the titration force curve for low salt concentration as a peak. This peak changes to a sigmoidal shape at higher salt concentrations. The appearance of a peak is attributed to the formation of strong hydrogen bonds between the tip and the substrate as reported in the literature. The effect of the ionic strength on the force curves is explained by the condensation of counterions on the carboxylate groups. At high pH, the adhesion force almost vanishes. On the approach, at high pH, one first observes repulsion between the tip and the substrate, which varies exponentially with the tip/substrate distance. The decay length of this repulsion force is in good agreement with theoretical predictions of the Debye length, attesting to the electrostatic nature of the interactions. We also find that the replacement of monovalent cation K+ by the divalent cation Ca2+ leads to significant changes in the force titration curve at high pH where the dicarboxylic groups are fully ionized. We observe that the adhesion force no longer vanishes at high pH but even slightly increases with pH, an effect that is explained by Ca2+ ions bridging between two carboxylate groups.
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