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.
Stimuli‐responsive materials have properties that depend on the environment in which they are used. In most cases, the material itself is formulated to react to the corresponding stimulus. However, ...many phenomena occur at the surface of the material. In this context, the design and the investigation of the reactivity of stimuli‐responsive surfaces are particularly interesting. More precisely, this review focuses on functional coatings that react via Diels–Alder (DA) chemistry, a thermoreversible reaction between a diene and a dienophile. According to the nature of the substrate, these coatings are mainly based on self‐assembled monolayers or silane assemblies, on polydopamine derivatives, or on polymer thin films deposited by vapor‐phase processes including plasma polymerization. The different works discussed here show that interfacial thermoreversible reactions occur between a DA‐functionalized surface and a DA reactant in solution but also between two solid substrates are possible. The direct cycloaddition is always described in the cited papers but the reversibility of the reaction is less discussed. The latter however remains very challenging for smart applications in material science.
This review reports on the fabrication of functional surfaces with thermoreversible properties and the understanding of their reactivity via the Diels–Alder reaction. Based on various functionalization processes, the designed surfaces have various physico‐chemical properties, leading to different Diels–Alder reactivity. The direct cycloaddition is always described in the cited papers but the reversibility of the reaction is less discussed.
The plasma polymerization of hexamethyldisiloxane (HMDSO) leads to the environmentally friendly fabrication of water-repellent coatings through a vapor-phase surface functionalization process using ...alternatives to the controversial perfluoroacrylate precursors. However, the durability of these coatings is their Achilles’ heel, which requires an in-depth study of the relationship between the structure and properties of these thin films in order to propose concrete solutions for the fabrication of fluorine-free water-repellent textiles. In this context, HMDSO plasma polymers have been deposited on cotton fabrics in an original reactor that allows easy tuning of temporal and spatial parameters of the glow discharge. The functionalized fabrics were characterized to gain insights into the chemical composition of the coatings, their morphology and, above all, their adhesion properties. Interestingly, the results after washing tests revealed a significant dependence of the durability of the superhydrophobic property on the elastic modulus of the deposited polymer. The formation of some radicals at the substrate–thin film interface in the early stages of deposition also correlates with some results. These relationships between the operating conditions of the plasma polymerization, the interfacial properties and the performances of the functionalized fabrics, but also the characterization methodology developed in this work, can undoubtedly serve the engineering of water-repellent fluorine-free coatings on fabrics with optimal durability.
•Carbamation of cellulose nanocrystals with TDI obtained at various surface DS.•Efficiency of grafting different Diels-Alder moieties onto CNCs surface assessed.•Thorough spectroscopy ...characterization of functionalized CNCs.
The Diels-Alder reaction is a promising click chemistry for the design of advanced materials from cellulose nanocrystals (CNCs). Transferring such chemistry to cellulose nanocrystals requires the precise grafting of reactive Diels-Alder moeities under heterogeneous conditions without compromising the nanocrystals morphology. In this study toluene diisocyanate is used as a spacer to graft Diels-Alder moieties viz the furyl and protected maleimido moieties onto cellulose nanocrystals. A factorial experimental design reveals that reaction time and reactant molar ratio positively affect the grafting efficiency, as evidenced by FTIR and CHNS elemental analysis. The surface degree of substitution was analyzed via CHNS elemental analysis and XPS and found to range between 0.05 to 0.30, with a good agreement between the two techniques. 13C CP/MAS NMR confirmed that the grafted moieties and CNCs are intact after reaction. Side reactions were also observed and their impact on performing controllable click chemistry between cellulose nanocrystals is discussed.
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.
Weather conditions and the Brazilian fertile soil contribute to abundant natural resources in a wide variety of fiber types. These fibers have attracted interest in Materials Science area for such ...characteristics as: low cost, high elasticity modulus and renewability. In this context, the objective of this work was physical, chemical and morphological characterization of purple banana fibers (Musa velutina). The following characterizations were employed: TG, DSC, FTIR, XRD, SEM, density, mechanical properties and chemical composition. The results showed that the purple banana fibers had good thermal, mechanical, morphological and structural properties. Treatment with sodium hydroxide was efficient in removing amorphous regions present on the fiber as evidenced by the chemical composition, increasing the crystallinity index. Therefore, the purple banana fiber is promising as reinforcement in polymer matrices.
Several alternatives have been considered to minimize the environmental impact caused by conventional polymers. This study aims to evaluate the chemical, mechanical and morphological properties of ...flexible thermoplastic films of cassava and corn starch, using glycerol and lignin as plasticizers and reinforcement. The films were produced through casting. It was observed that the presence of lignin effectively increased the maximum stress and the elastic modulus by about of 840% and 4200%, respectively, when comparing to the film containing only glycerol. In addition, lignin improved thermal properties, modified some structural properties and made the surface of the material rougher.
The properties of the final product resulting from plasma polymerization strongly depend on the operating conditions and they impact the final application of the plasma polymer coating. Low‐pressure ...pulsed plasma polymerization of maleic anhydride was investigated at two different positions in relation to the glow discharge in a 1‐m‐long tubular reactor. Interestingly, competition was observed in the deposition of maleic anhydride plasma polymer in the form of a smooth thin film versus that in the form of nanoparticles. The possibility of a spatiotemporal control of plasma polymerization enabled the deposition of a plasma coating with tunable morphological properties depending on the sample position from the glow discharge and on the plasma pulse parameters (on‐time and off‐time).
Low‐pressure pulsed plasma polymerization of maleic anhydride was investigated at two different positions in relation to the glow discharge in a tubular reactor. Interestingly, competition was observed in the deposition of maleic anhydride plasma polymer in the form of a smooth thin film versus that in the form of nanoparticles. The morphology of the plasma polymer coating could be tailored by selecting the appropriate sample position from the glow discharge and plasma pulse parameters (on‐time and off‐time).
Biodegradable films are widely exploited among scientists nowadays. Their positive environmental impact, besides their potential to promote better food conservation and an increase in shelf life ...motivate research in this field. Availability, low cost and biodegradability of starch increase the interest of using this material to produce biodegradable films. However, starch films tend to be brittle and they need addition of a plasticizer to enable their usage. In this work, starch films were synthesized with different carboxylic acids as plasticizers, aiming to observe the effect of the acids' chain size in the final films properties. Oxalic, succinic and adipic acids were used. The materials were produced by casting and characterized by DSC, TG, XRD, FTIR and SEM. It was observed that the acids chain size influenced on the thermal and structural properties of the films.
Given the limited resources and the growing demand for critical metals as well as the strict environmental regulations, it is essential to develop new metals recovery technologies (more efficient, ...less expensive and environmentally friendly) especially concerning the treatment of high volume of diluted wastes. In this sense, continuous flow processes appear as the best alternative. But this approach requires suitable adsorbents in term of low pressure drop and ability to adsorb ppm or even ppb traces of metal which are sine qua non key-features. Herein, we have modified the surface of a commercially available open cell melamine foam using the mussel inspired chemistry through an original and ultrafast process. This non-toxic bioinspired coating is based on the polymerization of polyphenols such as dopamine leading to a commonly called polydopamine (PDA) layer resulting to me@PDA adsorbent. Using Pb(II) as model, we have demonstrated its efficient adsorption even from ppb level, leading to a capacity of 1.2 mmol.g−1 determined from a continuous process. By increasing the path passing through me@PDA, it is observed an increase of the Pb(II) loading capacity concomitantly with the PDA mass. Since me@PDA is an elastic adsorbent, its compression in the filtration column to insert more foam results in an increase of Pb(II) adsorbed without significant increase of the pressure drop. Furthermore, desorption is obtained using a flow of acid solution. Finally, the similarity of three successive cycles of adsorption-desorption of Pb(II) highlights the repeatability of the process and the chemical robustness of the adsorbent me@PDA as designed.
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•Ultrarapid PDA deposition based on the compression-decompression of melamine foam.•The resulting me@PDA is a low-cost, robust and flexible adsorbent.•me@PDA adsorbs ppm/ppb of Pb(II) in a continuous process with a low pressure drop.•Adsorption/desorption cycles were realized without loss of the me@PDA efficiency.•Compression allows higher specific surface in a given volume increasing adsorption.
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