Dipolar glass polymers containing polarizable groups as dielectric materials for energy storage applications. A minireview

Materials that have high dielectric constants, high energy densities and minimum dielectric losses are highly desirable for use in capacitor devices. In this sense, polymers and polymer blends have several advantages over inorganic and composite materials, such as their flexibilities, high breakdown strengths, and low dielectric losses. Moreover, the dielectric performance of a polymer depends strongly on its electronic, atomic, dipolar, ionic, and interfacial polarizations. For these reasons, chemical modification and the introduction of specific functional groups (e.g., F, CN and R−S(=O)2−R´) would improve the dielectric properties, e.g., by varying the dipolar polarization. These functional groups have been demonstrated to have large dipole moments. In this way, a high orientational polarization in the polymer can be achieved. However, the decrease in the polarization due to dielectric dissipation and the frequency dependency of the polarization are challenging tasks to date. Polymers with high glass transition temperatures (Tg) that contain permanent dipoles can help to reduce dielectric losses due to conduction phenomena related to ionic mechanisms. Additionally, sub-Tg transitions (e.g., γ and β relaxations) attributed to the free rotational motions of the dipolar entities would increase the polarization of the material, resulting in polymers with high dielectric constants and, hopefully, dielectric losses that are as low as possible. Thus, polymer materials with high glass transition temperatures and considerable contributions from the dipolar polarization mechanisms of sub-Tg transitions are known as “dipolar glass polymers”. Considering this, the main aspects of this combined strategy and the future prospects of these types of material were discussed

Optical, morphological and photocatalytic properties of biobased tractable films of chitosan/donor-acceptor polymer blends

Biobased tractable films consisting of blends of chitosan (CS) with polymer bearing carbazole derivatives as pendant groups and fluorene-thiophene as donor-acceptor units (referred to as DA) were prepared, and their optical, morphological and photocatalytic properties were studied. DA was dissolved in tetrahydrofuran (THF) and mixed with an acidified aqueous solution containing chitosan to obtain chitosan/DA (CS/DA) films by solution casting. The fabricated biobased films were characterized using spectroscopic techniques (FT-IR and UV–vis), thermogravimetry, mechanical assays, contact angle analysis, and atomic force microscopy (AFM). The effects of varying DA compositions and the results of exposure to visible-light irradiation of the films were also analyzed. The results indicated the existence of interactions between chitosan and DA and a potentially profitable light-driven response of these biobased films. This behavior was reflected in the optical, topographical, and contact angle properties of the films, which exhibited different characteristics before and after visible-light exposure. Finally, the photocatalytic performance of the biobased films was tested via the decomposition of methyl orange (MO), as a reaction model system. Our results revealed a significant photocatalytic activity (according to biobased film composition, approximately 64 % and 87 % of methyl orange were degraded under continuous visible-light irradiation for 120 min) of the films which is attributed to the combined presence and synergetic effects of the film-forming ability of chitosan and the photoproperties of DA

Novel 3D copper nanoparticles/chitosan/nanoporous alumina (CCSA) membranes with catalytic activity. Characterization and performance in the reduction of methylene blue

Herein, we report the surface modification of H2O2-treated nanoporous alumina (anodic aluminum oxide, MO) membranes with chitosan (CS) by a solution casting method. Later, copper nanoparticles were incorporated into this CS-AAO membrane by immersion in an aqueous solution of a copper salt precursor and subsequent reduction using NaBH4. The IR spectra and energy dispersive X-ray spectroscopy (EDS) analyses helped to confirm the presence of CS and copper nanoparticles both on the surface and inside the nanochannels of this AAO membrane (denoted CCSA). Notable differences in the surface energy, surface topography and morphology were observed between the CS-AAO and CCSA membranes. The catalytic performance of the CCSA membrane was tested in the reduction of methylene blue (MB).Our findings revealed that this system adequately combines the attractive properties of supporting of the AAO membranes, ion retention by CS and the catalytic activity of copper nanoparticles into a tridimensional array. Finally, the recyclability of the CCSA membrane was also assessed. The results showed that the performance of this membrane was not dramatically affected after four cycles of use. (C) 2018 Elsevier Ltd. All rights reserved

Optical and electronic activities of biobased films of chitosan/POTE containing gold nanoparticles: Experimental and theoretical analyses

Biobased films consisting of blends of chitosan with poly(octanoic acid 2-thiophen-3-yl-ethyl ester) (POTE), a conducting polymer, and gold nanoparticles (AuNPs) were prepared, and their thermal, morphological and surface potential properties were studied. POTE was dissolved in THE and mixed with an acidified aqueous solution containing chitosan to obtain chitosan/POTE (CS/POTE) films by solution casting. To produce gold nanoparticles in the CS/POTE films (i.e., CS/POTE/AuNP films), an aqueous solution of KAuCl4 salt at fixed concentration was added to the initial chitosan solution. The fabricated biobased films were characterized by spectroscopic techniques (FT-IR and UV-visible), thermogravimetry, contact angle analysis, polarized light microscopy (PLM), field emission scanning electron microscope (FE-SEM) and scanning Kelvin probe force microscopy (SKPFM). The effects of varying POTE composition and the presence of gold nanoparticles in the films were analyzed. For example, the results indicated the existence of interactions between chitosan and POTE, and LPM studies revealed a predominantly amorphous nature of these biobased films. In addition, the optical and surface potential behaviors of the films were examined by UV visible and KPFM techniques. From the UV visible spectra, the optical band gaps were estimated for the samples, and their surface potential maps exhibited differences according to the composition of POTE and the presence of AuNPs. Finally, theoretical electronic calculations provided insight into the contributions of POTE and gold nanoparticles to the electronic activity of the films