Polyelectrolyte complexes (PECs) are prepared by mixing solutions of oppositely charged polyelectrolytes. These diffuse, amorphous precipitates may be compacted into dense materials, CoPECs, by ...ultracentrifugation (ucPECs) or extrusion (exPECs). The presence of salt water is essential in plasticizing PECs to allow them to be reformed and fused. When hydrated, CoPECs are versatile, rugged, biocompatible, elastic materials with applications including bioinspired materials, supports for enzymes and (nano)composites. In this review, various methods for making CoPECs are described, as well as fundamental responses of CoPEC mechanical properties to salt concentration. Possible applications as synthetic cartilage, enzymatically active biocomposites, self‐healing materials, and magnetic nanocomposites are presented.
When plasticized by salt water, polyelectrolyte complexes prepared by mixing solutions of oppositely charged polyelectrolytes can be compacted and processed by ultracentrifugation or extrusion. These hydrated materials are tough, stretchable and self‐healing. Examples of applying these “saloplastics” as biomaterials, enzyme supports, and magnetic nanocomposites are presented.
•Emerging strategies for electrochemical nanoarchitectonic are extensively reviewed.•Applications to capacitors, electrochromism, sensing, corrosion, water splitting.•Fundamental electrochemistry on ...nanoarchitectonic-based LbL films is reviewed.•A special emphasis has been put on electroclick and carbazole chemistry approaches.•Applications for patterning, solar cells and biofunctional surfaces are summarized.
During the last few decades, electrochemistry and electrode modification have seen a tremendous fall off in creativity with the emergence of the nanoarchitectonic-based layer-by-layer (LbL) film deposition technique. An unprecedented variety of building blocks can be immobilized on surfaces, leading to progress in several fields including sensing, electrochromic, electro-responsive and energy devices. This review describes the state of the art of electrochemical devices based on LbL assemblies, with a focus on supercapacitors, biosensors, and electroresponsive LbL such as electrodissolution/electroswelling of coatings. Recently, electrochemistry has also been used as an “active trigger” to induce the formation of films by covalent coupling, leading to new nanoarchitectonic approaches beyond the LbL strategy. These emerging electro-coupling reactions, including electroclick and carbazole chemistry, open new perspectives toward architecture and patterning of functional films and are extensively reviewed.
Cells and bacteria use mechanotransduction processes to transform a mechanical force into a chemical/biochemical response. The area of chemistry where chemical reactions are induced by mechanical ...forces is called mechanochemistry. Over the last few years, chemists developed force-induced reactions affecting covalent bonds in molecules under tension which requires high energy input and/or high intensity forces. In contrast, in nature, mechanotransduction processes take place with forces of much weaker intensity and much less demanding energy. They are mainly based on protein conformational changes or changes in supramacromolecular architectures. Mechanochemistry based on such low-energy-demanding processes and which does not affect chemical bonds can be called soft-mechanochemistry. In this feature article, we first discuss some examples of soft-mechanochemistry processes encountered in nature, in particular, cryptic sites, allowing us to define more precisely the concepts underlying soft-mechanochemistry. A series of examples, developed over the past few years, of chemomechanoresponsive systems based on soft-mechanochemistry principles are given. We describe, in particular, cryptic site surfaces, enzymatically active films whose activity can be modulated by stretching and films where stretching induces changes in their fluorescence properties. Finally, we give our view of the future of soft-mechanochemistry.
Localized molecular self‐assembly processes leading to the growth of nanostructures exclusively from the surface of a material is one of the great challenges in surface chemistry. In the last decade, ...several works have been reported on the ability of modified or unmodified surfaces to manage the self‐assembly of low‐molecular‐weight hydrogelators (LMWH) resulting in localized supramolecular hydrogel coatings mainly based on nanofiber architectures. This Minireview highlights all strategies that have emerged recently to initiate and localize LMWH supramolecular hydrogel formation, their related fundamental issues and applications.
From the bottom to the top: Spatial control of the self‐assembly can be triggered by the surface itself. Different strategies have been developed to grow supramolecular hydrogels at the solid–liquid interface.
The alternate deposition of polyanions and polycations on a solid substrate leads to the formation of nanometer to micrometer films called Polyelectrolyte Multilayers. This step‐by‐step construction ...of organic films constitutes a method of choice to functionalize surfaces with applications ranging from optical to bioactive coatings. The method was originally developed by dipping the substrate in the different polyelectrolyte solutions. Recent advances show that spraying the polyelectrolyte solutions onto the substrate represents an appealing alternative to dipping because it is much faster and easier to adapt at an industrial level. Multilayer deposition by spraying is thus greatly gaining in interest. Here we review the current literature on this deposition method. After a brief history of polyelectrolyte multilayers to place the spraying method in its context, we review the fundamental issues that have been addresses so far. We then give an overview the different fields where the method has been applied.
Design of nanometer to micrometer thin films by spraying solutions of polyelectrolyte is a recent emerging concept in the field of surface coating. Herein the origin of this new process, the fundamental issues, and the resulting potential applications relative to spray assisted deposition from the current literature are reviewed.
The deposition of surface coatings using a step‐by‐step approach from mutually interacting species allows the fabrication of so called “multilayered films”. These coatings are very versatile and easy ...to produce in environmentally friendly conditions, mostly from aqueous solution. They find more and more applications in many hot topic areas, such as in biomaterials and nanoelectronics but also in stimuli‐responsive films. We aim to review the most recent developments in such stimuli‐responsive coatings based on layer‐by‐layer (LBL) depositions in relationship to the properties of these coatings. The most investigated stimuli are based on changes in ionic strength, temperature, exposure to light, and mechanical forces. The possibility to induce a transition from linear to exponential growth in thickness and to change the charge compensation from “intrinsic” to “extrinsic” by controlling parameters such as temperature, pH, and ionic strength are the ways to confer their responsiveness to the films. Chemical post‐modifications also allow to significantly modify the film properties.
The stimuli‐responsive properties of films deposited in a layer‐by‐layer manner are reviewed herein in relation to their physicochemical properties. The ability of these films to grow either linearly or exponentially with the number of deposition steps as well as their charge compensation mode allows the fine‐tuning of their dynamic response to external stimuli, such as pH changes, changes in temperature, or mechanical stresses.
The inherent room temperature mending and self‐healing properties of saloplastic PAA/PAH CoPECs are studied. After ultracentrifugation of PAA/PAH polyelectrolyte complexes, tough, elastic materials ...are obtained that undergo self‐healing facilitated by salt. At intermediate salt concentrations the CoPECs remain elastic enough to recover their original shape while the chains are mobile enough to repair the cut, thus leading to actual self‐healing behavior.
It has recently been demonstrated that dopamine solutions put in contact with a variety of solid substrates allow the production of thin coatings probably made of melanin ( Science 2007, 318, 426 ). ...In this article, we show that the thickness of these coatings can be controlled to allow a growth regime that is proportional to the reaction time if fresh dopamine is regularly provided. We propose that the growth is initiated by the adsorption of a radical compound. When dopamine polymerization or aggregation has reached a steady state in solution, the produced species do not adhere anymore to the substrate, emphasizing the role played by unoxidized dopamine. X-ray photoelectron spectroscopy showed that the thickness of the deposit increases linearly with the number of immersion steps, but the thickness measured in ultravacuum is about 4 times smaller than the thickness measured by ellipsometry in conditions of ambient humidity. This suggests that the drying of the deposit has a considerable influence on its properties. The Si2p signal characteristic of the silicon substrate decreases progressively when the number of deposition steps increases but does vanish even after 32 deposition steps. This observation will be discussed with respect to the formation of a continuous film. Cyclic voltammetry experiments showed that a deposit impermeable to ferrocyanide is obtained after the immersion in nine freshly prepared dopamine solutions, demonstrating the formation of a film. The atomic composition of the film determined by X-ray photoelectron spectroscopy is compatible with that of melanin. Finally, we show that the deposit can be quantitatively removed from the substrate when put in a strongly alkaline solution.
Inspired by biology, one current goal in supramolecular chemistry is to control the emergence of new functionalities arising from the self‐assembly of molecules. In particular, some peptides can ...self‐assemble and generate exceptionally catalytically active fibrous networks able to underpin hydrogels. Unfortunately, the mechanical fragility of these materials is incompatible with process developments, relaying this exciting field to academic curiosity. Here, we show that this drawback can be circumvented by enzyme‐assisted self‐assembly of peptides initiated at the walls of a supporting porous material. We applied this strategy to grow an esterase‐like catalytically active supramolecular hydrogel (CASH) in an open‐cell polymer foam, filling the whole interior space. Our supported CASH material is highly efficient towards inactivated esters and enables the kinetic resolution of racemates. This hybrid material is robust enough to be used in continuous flow reactors, and is reusable and stable over months.
CASH flow: Catalytically active supramolecular hydrogels (CASHs) generated from a porous polymer foam by an enzyme‐assisted self‐assembly strategy are ideal catalytic phases for continuous flow. A hydrogel prepared from an original bis‐phosphorylated heptapeptide enables highly efficient ester hydrolysis and kinetic resolution.
The diffusion of adequate peptide through an enzyme-embedded host hydrogel leads to the in situ start-up and growth of an interpenetrated fibrous network. Based on the enzyme-assisted self-assembly ...concept, both chemistry and mechanical features of the hybrid hydrogel can be tuned.
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