Interfacial Thermoreversible Chemistry on Functional Coatings: A Focus on the Diels–Alder Reaction

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.     

A new approach for design of organic electrochromic devices with inter-digitated electrode structure

We present a new approach for design of organic electrochromic devices (ECD) with inter-digitated electrode (IDE) structure and three-electrode dynamic operation. The advantages of the IDE design include the ability to produce fast and homogenous color change over large areas. In addition, it enables fabrication of multi-color devices. Our method involves photolithographic etching of ITO followed by electrophoretic deposition (EPD) and mechanical compression of porous titania to produce finely patterned electrodes with high surface area. The titania layer is chemically modified by new stable and reversible electrochromic viologen derivatives involving phenylphosphonic acid anchoring moiety. The new device demonstrates reversible and strong color change from colorless to deep blue and yellow.     

Dyeability of corona-treated fabrics

In this study, corona technology is applied in the wet processing of cotton fabrics. The properties of cotton, such as hydrophilicity, ionisation and mechanical properties, are evaluated and compared with previous results of cuticle oxidation and morphological changes. The results of dyeings of coronatreated materials under different conditions are compared with those of raw, bleached and desized cotton. The dyeings are carried out with three different commercial direct dyes. The classical method for the processing of cotton materials and the corona discharge method are discussed and compared in order to analyse the advantages of this innovative process.     

Origin of crystallization-induced refractive index changes in photo-thermo-refractive glass

Photo-thermo-refractive (PTR) glass is a multi-component silicate that undergoes localized refractive index decrease after UV-exposure and thermal treatment for partial crystallization. Based on this refractive index change, high efficiency volume Bragg gratings have been developed in PTR glass and have been successfully used for laser beam control. However, despite the fact that this type of glass has been widely studied and used over the last 20 years, the origin of the refractive index change upon crystallization is poorly understood. In this paper, we introduce three possible mechanisms (the precipitation of nano-sized NaF crystals and the associated local chemical changes of the glass matrix, the volumetric changes due to relaxation, and the local residual stresses) for the refractive index decrement in PTR glass and estimate the partial refractive index change due to each mechanism. Refractive index measurements are compared with high temperature XRD experiments and a general approach for the simulation of the refractive index change in PTR glass is proposed. We show that among the studied variables the residual stresses surrounding the crystals are the main responsible for the local refractive index decrement in this glass.     

Synthesis,characterization and antibacterial activity studies of poly-{styrene-acrylic acid} with silver nanoparticles

This work reports the preparation and characterization of copolymer poly-{styrene-acrylic acid} with monomeric ratio of styrene/acrylic acid of 9:1 using benzoyl peroxide as initiator and furthermore filled with nanosilver (25 ppm and 50 ppm) in water/acetone (1:40 v/v). The nanosilver emulsion was obtained from chemical reduction using NaBH₄ as reducing agent and sodium citrate as the stabilizer. The preparation of nanosilver emulsion was monitored by the appearance of a Plasmon Resonant Absorption band in a UV–visible spectrophotometer and the particles sizes were observed through TEM. Microbiological studies were performed to investigate the antimicrobial activity of this new material against the microorganisms Escherichia coli (ATCC-25922) and Staphylococcus aureus (ATCC-6538), used as reference strains. The antimicrobial activity of the poly-{styrene-acrylic acid} filled with nanosilver was confirmed by the presence of an inhibition halo of the bacterial growth in seeded culture media, but was not found with the poly(styrene-acrylic acid) alone. The present work suggests that silver ions are released from the polymeric matrix to the culture media and have the ability to tune the Ag⁺ ions released by controlling the amount of Ag nanoparticles embedded in the composite.     

Development and characterization of wheat gluten microspheres for use in a controlled release system

The purpose of this study was the development and characterization of wheat gluten microspheres for use as controlled release devices, and the evaluation of the effect of the addition of poly (ethylene glycol) (PEG). Diltiazem hydrochloride was used as the model drug in the in vitro release essay. The physical–chemical and morphological properties of the microspheres were evaluated, as well as their encapsulation efficiency. Porosity varied with the presence or absence of PEG. The diltiazem encapsulation efficiency was 72.8% and 96.7% for wheat gluten and gluten/PEG 95/05 microspheres, respectively. The DSC and FTIR results indicated interactions between the microparticles and additives used. In the in vitro release tests it was observed that, for all the studied systems, the burst effect occurred in the first 2 h of release and the microspheres prepared with PEG had a faster release rate. In the attempt to elucidate the release mechanism, the systems were treated based on two well known mathematical models: the Higuchi and the power law. It was found that the microsphere release mechanism is not exclusively diffusion-controlled and, probably, the release occurs through a combination of partial diffusion through the swelling matrix and hydrophilic pores.     

Responses to powerlessness: Stereotyping as an instrument of social conflict.

In the context of recent arguments that stereotyping plays an important role in the subjugation of powerless groups, this article explores the possibility that stereotyping may also contribute to social change processes engaged in by the disadvantaged. In a partial replication of an experiment by S. C. Wright, D. M. Taylor, and F. M. Moghaddam (1990), participants (N?=?44) were placed in powerless, low-status groups and denied entry to an attractive high-status group. The intergroup boundary was open, slightly permeable, or completely impermeable. Participants could respond to this disadvantage in 1 of 3 ways: acceptance, individual protest, or collective protest. As predicted, open boundaries produced acceptance and reproduction of stereotypes consistent with the established status relationship, whereas closed boundaries encouraged collective protest and stereotypes that challenged the powerful group's position. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Collector-Shell Mesoporous Electrodes for Dye Sensitized Solar Cells

We present results for dye sensitized solar cell (DSSC) electrodes based on high surface area indium tin oxide (ITO) coated with an active TiO₂ layer. This design, denoted as a “collector-shell electrode”, ensures a distance of several nanometers between the TiO₂-electrolyte interface and the current collector throughout the porous electrode, in contrast to several micrometers associated with the standard electrode. The new design also enables an inherent screening capability due to the high doping level of the conductive core matrix. Therefore, the importance of this electrode configuration is its ability to overcome the collection and image field problems in DSSCs, especially for solid-state hole–conductor-based devices. Efficiencies of 1.37% for cells containing ITO-TiO₂ collector-shell electrodes and 1.63% for similar electrodes that received an additional coating of a thin MgO layer were achieved. We expect greater cell performance improvement after optimization of the nature and the size of conductive material particles, the TiO₂ shell thickness and uniformity, and the barrier layer(s) properties.     

PBAT/TPS-nanowhiskers blends preparation and application as food packaging

About 85–90% of the market for new materials in biodegradable packaging is served by various blends and composites containing starch in some portion. In an attempt to satisfy the increasing consumer demand, innovative materials are being developed. This includes the concept of active packaging, which, in addition to protecting, interacts with the packaged product. In this context, flexible films have been prepared from blends of poly(butylene adipate-co-terephthalate), thermoplastic starch (TPS), and cellulose nanowhiskers (CNW) at different concentrations (0–3.0 wt %) and with distinct compatibilizing agents (glycerol, stearic acid, and citric acid) by flat extrusion. Palm oil was packaged in the films, and was stored under accelerated oxidation conditions as a model system. The films were also used for packing lettuce. The TPS increased the rate of water vapor permeability of the blends. The micrographs showed the films with very porous surface as a function of the CNW concentration. In addition to the antimicrobial action pronounced within 10 days (fungi—molds and yeasts; bacteria—mesophilic and psychrotrophic), the film showed a prooxidant action, indicating its suitability for fruit and vegetable packaging. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47699.