Multicolor Electrochromics: Rainbow-Like Devices.

Stimuli-responsive reversible coloration-change materials represent a highly demanded type of smart systems useful for a wide variety of applications, with a significant growing interest in multicolor abilities. In particular, electrochromic materials have received a great deal of attention due to their versatility and broad range of industrial uses. However, most of the existing electrochromic technologies provide a single coloration, while achieving multiple colors based on simple approaches remains a challenge. The present article reports on PVA gel-based electrochromic devices, containing a single viologen, providing a colorless and two different well-defined colored states. The successful fabrication of a device, based on two viologens (multi-EC gel) with a simple architecture (glass/TCO/multi-EC gel/TCO/glass), with five different multiswitchable colors based on four-zoned electrodes (rainbow-like ECD) is also demonstrated. This novel easy-to-make multichromic system represents a significant breakthrough toward the generation of full-color devices, expanding the potential of electrochromic technology.

Functionalization of Cellulose Nanocrystals in Choline Lactate Ionic Liquid.

Cellulose nanocrystals (CNCs) are valuable nanomaterials obtained from renewable resources. Their properties make them suitable for a wide range of applications, including polymer reinforcement. However, due to their highly hydrophilic character, it is necessary to modify their surface with non-polar functional groups before their incorporation into a hydrophobic polymer matrix. In this work, cellulose nanocrystals were modified using a silane coupling agent and choline lactate, an ionic liquid derived from renewable resources, as a reaction medium. Modified cellulose nanocrystals were characterized by infrared spectroscopy, showing new peaks associated to the modification performed. X-ray diffraction was used to analyze the crystalline structure of functionalized cellulose nanocrystals and to optimize the amount of silane for functionalization. Poly(lactic acid) (PLA) nanocomposites containing 1 wt % of functionalized cellulose nanocrystals were prepared. They were characterized by field-emission scanning electron microscopy (FE-SEM) and mechanical tests. The use of choline lactate as reaction media has been shown to be an alternative method for the dispersion and silanization of the cellulose nanocrystals without the addition of an external catalyst.

Injectable and Self-Healing Dynamic Hydrogels Based on Metal(I)-Thiolate/Disulfide Exchange as Biomaterials with Tunable Mechanical Properties.

Despite numerous strategies involving dynamic covalent bonds to produce self-healing hydrogels with similar frequency-dependent stiffness to native tissues, it remains challenging to use biologically relevant thiol/disulfide exchange to confer such properties to polymeric networks. Herein, we report a new method based on Metal(I) [Au(I) or Ag(I)] capping to protect thiolates from aerial oxidation without preventing thiolate/disulfide exchange. Dynamic hydrogels were readily prepared by injecting simultaneously aqueous solutions of commercially available HAuCl4 and 4-arm thiol-terminated polyethylene glycol [(PEGSH)4], resulting in a network containing a mixture of Au(I)-thiolate (Au-S) and disulfide bonds (SS). While the dynamic properties of the hydrogel were closely dependent on the pH, the mechanical properties could be easily tuned by adjusting (PEGSH)4 concentration and amount of Au-S, as judged by dynamic rheology studies. Permanent Au-S/SS exchange at physiological pH conferred self-healing behavior and frequency-dependent stiffness to the hydrogel. In addition, in vitro studies confirmed that Au-based dynamic material was not cytotoxic to human dermal fibroblasts, demonstrating its potential use as a medical device. Dynamic hydrogels obtained using Ag(I) ions demonstrated that the exchange reaction was not affected by the nature of the Metal(I) capping. Finally, this efficient thiolate capping strategy offers a simple way to produce injectable and self-healing dynamic hydrogels from virtually any thiol-containing polymers.

Aurophilically cross-linked "dynamic" hydrogels mimicking healthy synovial fluid properties.

We report a new supramolecular dynamic hydrogel, based on a new concept of reversible aurophilic cross-linkers, mimicking the rheological behaviour of healthy synovial fluid under physiological conditions with good cell viability.

Facile and scalable synthesis of nanoporous materials based on poly(ionic liquid)s.

A simple, fast, sustainable, and scalable strategy to prepare nanoporous materials based on poly(ionic liquid)s (PILs) is presented. The synthetic strategy relies on the radical polymerization of crosslinker-type ionic liquid (IL) monomers in the presence of an analogous IL, which acts as a porogenic solvent. This IL can be extracted easily after polymerization and recycled for further use. The great advantages of this synthetic approach are the atom-efficiency and lack of waste. The effects of different monomer/porogen ratios on the specific surface area, porosity, and pore size have been investigated. Finally, the potential of the materials as CO2 sorbents has been evaluated.

Flexible viologen electrochromic devices with low operational voltages using reduced graphene oxide electrodes.

Reduced graphene oxide (RGO) films have been electrodeposited on indium tin oxide-coated polyethylene terephthalate (ITO-PET) substrates from graphene oxide (GO) solutions, and the resulting flexible transparent electrodes have been used in electrochromic devices of ethyl viologen (EtV(2+)). The electrochromic performance of devices with bare ITO-PET electrodes and ITO-PET coated with RGO has been compared. Under continuous cycling tests up to large voltages, the RGO film was oxidized and dispersed in the electrochromic mixture. The resulting devices, which contained GO and RGO in the electrochromic mixture, showed lower switching voltages between the colored and bleached states. This electrocatalytic activity of the solution-phase GO/RGO pair toward the electrochemical reaction of the electrochromic redox couple (the dication EtV(2+) and the radical cation EtV(+•)) allowed devices with an optical contrast higher than the contrast of those free of GO at the same applied voltage.

Room temperature self-healing power of silicone elastomers having silver nanoparticles as crosslinkers.

Thiol-functionalised silicone-oils were crosslinked with silver nanoparticles to give mechanically consistent elastomers with high self-healing power. The materials were broken into small pieces and put together in intimate contact for 24 hours at room temperature, observing a complete macroscopic healing and a quantitative recovery of compression-stress and strain.

Single-chain polymer nanoparticles.

The synthesis of polymer nanoparticles (NPs) with controlled characteristics has become an appealing research topic lately. Nanomedicine, and especially drug delivery and imaging, are fields that require particles of a controlled size and with a tailored arrangement of functional groups. Intramolecular cross-linking or collapse of single polymer chains has emerged as an efficient alternative for the synthesis of well-defined polymer NPs. This technique allows the generation of 1.5-20 nm particles with a wide variety of chemical compositions and functionalities. This review begins by gathering synthetic strategies described in the literature and groups them into four main synthetic methods: homo-functional collapse, hetero-functional collapse, crosslinker-mediated collapse, and one-block collapse of diblock or triblock copolymers. Afterwards, the main characterization techniques and physical properties of single-chain polymer NPs (SCPNs) are exposed. Finally, several applications in nanomedicine are mentioned followed by some future perspectives.

Designing neutral metallophilic hydrogels from di- and tripeptides.

Here we report the metallophilic attraction driven gel-forming capability of four cysteine-containing short peptides at neutral pH. Such peptides were designed to have an isoelectric point (pI) close to 7, aided by the introduction of an arginine unit with its highly basic guanidinium group.

Converting drugs into gelators: supramolecular hydrogels from N-acetyl-L-cysteine and coinage-metal salts.

Here we present the concept of metallophilic hydrogels, supramolecular systems in which the gelator species are metal-thiolates that self-assemble through metallophilic attractions. The principle is applied for a small drug, the mucolytic agent N-acetyl-l-cysteine (NAC), which readily forms hydrogels in the presence of Au(iii), Ag(i) and Cu(ii) salts. The resulting transparent hydrogels present pH induced sol/gel transition. Scanning electron microscopy (SEM) measurements reveal a microporous structure in form of flakes for the three of them. The low pH at which these hydrogels are formed (pH < 4) limits their direct use as drug-delivery systems, but still this system constitutes a novel method for easy and fast conversion of small drugs into potent hydrogelators. Future developments will help to fully develop the idea in order to create a new class of supramolecular drug-delivery systems.

Structural codons: linearity/helicity interconversion by pyridine/pyrimidine exchange in molecular strands.

Pyridine and pyrimidine groups connected through amide functions can be combined into specific sequences that self-organize into either helical or linear structures enforced by the formation of intramolecular hydrogen bonds.

Contraction/extension molecular motion by protonation/deprotonation induced structural switching of pyridine derived oligoamides.

NMR, mass spectrometry and X-ray diffraction studies show reversible structural interconversion between helical and extended forms of pyridine derived oligoamide molecular strands, by simple protonation/deprotonation.

Highly Diastereoselective Aldol Reactions with Camphor-Based Acetate Enolate Equivalents.

New lithium enolates of alpha-hydroxy ketones, derived from camphor, are evaluated for asymmetric aldol reactions in the presence of lithium chloride. The diastereoselectivity of the reactions between the lithium enolate of 3 and a variety of achiral aldehydes is strongly influenced by the lithium chloride salt. In these instances, the achieved levels of asymmetric induction, typically 95:5 dr, are in the range of those attained in aldol reactions involving the lithium enolate of the methyl ketone 4, which is sterically more demanding. The resulting aldol adducts are easily transformed into beta-hydroxy carboxylic acids, ketones, and aldehydes with concomitant recovery of the camphor, the chiral controller of the process, which can be reused.