Suppressing Dielectric Loss in MXene/Polymer Nanocomposites through Interfacial Interactions

Although numerous polymer-based composites exhibit excellent dielectric permittivity, their dielectric performance in various applications is severely hampered by high dielectric loss induced by interfacial space charging and a leakage current. Herein, we demonstrate that embedding molten salt etched MXene into a poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE))/poly(methyl methacrylate) (PMMA) hybrid matrix induces strong interfacial interactions, forming a close-packed inner polymer layer and leading to significantly suppressed dielectric loss and markedly increased dielectric permittivity over a broad frequency range. The intensive molecular interaction caused by the dense electronegative functional terminations (-O and -Cl) in MXene results in restricted polymer chain movement and dense molecular arrangement, which reduce the transportation of the mobile charge carriers. Consequently, compared to the neat polymer, the dielectric constant of the composite with 2.8 wt % MXene filler increases from ∼52 to ∼180 and the dielectric loss remains at the same value (∼0.06) at 1 kHz. We demonstrate that the dielectric loss suppression is largely due to the formation of close-packed interfaces between the MXene and the polymer matrix.

Dielectric, Thermal and Water Absorption Properties of Some EPDM/Flax Fiber Composites

This paper deals with the dielectric and sorption properties of some flax fiber-reinforced ethylene-propylene-diene monomer (EPDM) composites containing different fiber loadings as well as their behavior after exposure to different doses of electron beam irradiation. Three relaxation processes were evinced, a weak relaxation β at sub-Tg temperatures and two α-type relaxations above the Tg. The EPDM/flax composites exhibited higher values of dielectric constant, dielectric loss and conductivity as compared to a pristine EPDM sample. Using thermogravimetric analysis (TG) coupled with Fourier transform infrared spectroscopy (FTIR) and mass spectrometry (MS) (TG/FTIR/MS system), the degradation products can be identified. The water uptake increased as the flax fiber level increased in composites. The water uptake tests of irradiated composites showed that the highest water content was obtained for a flax fiber level of 20 phr.

New perspectives on development of polysulfones/cellulose derivatives based ionic-exchange membranes: Dielectric response and hemocompatibility study

Due to the increasing need from the membrane technologies for diverse applications, development of new generation of materials with electroactive properties and significant impact on the future technological systems was imposed. An innovative way of designing the membrane materials with long-term stable hydrophilicity, enhanced workability, porosity, and good biocompatibility, has been adopted by blending of quaternized polysulfone (PSFQ) with a cellulose derivative (cellulose acetate phthalate, CAP). Moreover, the quaternization effect has significantly improved the electrical performances, in terms of the ionic conductivity, electron interactions, and dielectric properties, required by target applications, i.e., ionic-exchange membranes, IEMs. Results derived from dielectric spectroscopy confirm the enhanced dielectric quality, reflected by a low dielectric constant and dielectric loss at high frequency. Additionally, the relationship between the resulted dielectric properties and response at the blood-biomaterial interface, have confirmed their excellent performance, constituting the preliminary basis for future tests concerning their functionality as IEMs in hemodialysis.

3D Analysis of Ordered Porous Polymeric Particles using Complementary Electron Microscopy Methods

Highly porous particles with internal triply periodic minimal surfaces were investigated for sorption of proteins. The visualization of the complex ordered morphology requires complementary advanced methods of electron microscopy for 3D imaging, instead of a simple 2D projection: transmission electron microscopy (TEM) tomography, slice-and-view focused ion beam (FIB) and serial block face (SBF) scanning electron microscopy (SEM). The capability of each method of 3D image reconstruction was demonstrated and their potential of application to other synthetic polymeric systems was discussed. TEM has high resolution for details even smaller than 1 nm, but the imaged volume is relatively restricted (2.5 μm)³. The samples are pre-sliced in an ultramicrotome. FIB and SBF are coupled to a SEM. The sample sectioning is done in situ, respectively by an ion beam or an ultramicrotome, SBF, a method so far mostly applied only to biological systems, was particularly highly informative to reproduce the ordered morphology of block copolymer particles with 32–54 nm nanopores and sampling volume (20 μm)³.

Functionalized Nanochannels from Self-Assembled and Photomodified Poly(Styrene-b-Butadiene-b-Styrene)

Membranes are prepared by self-assembly and casting of 5 and 13 wt% poly(styrene-b-butadiene-b-styrene) (PS-b-PB-b-PS) copolymers solutions in different solvents, followed by immersion in water or ethanol. By controlling the solution-casting gap, porous films of 50 and 1 µm thickness are obtained. A gradient of increasing pore size is generated as the distance from the surface increased. An ordered porous surface layer with continuous nanochannels can be observed. Its formation is investigated, by using time-resolved grazing incident small angle X-ray scattering, electron microscopy, and rheology, suggesting a strong effect of the air-solution interface on the morphology formation. The thin PS-b-PB-b-PS ordered films are modified, by promoting the photolytic addition of thioglycolic acid to the polybutadiene groups, adding chemical functionality and specific transport characteristics on the preformed nanochannels, without sacrificing the membrane morphology. Photomodification increases fivefold the water permeance to around 2 L m^-2 h^-1 bar^-1 , compared to that of the unmodified one. A rejection of 74% is measured for methyl orange in water. The membranes fabrication with tailored nanochannels and chemical functionalities can be demonstrated using relatively lower cost block copolymers. Casting on porous polyacrylonitrile supports makes the membranes even more scalable and competitive in large scale.

Asymmetric block copolymer membranes with ultrahigh porosity and hierarchical pore structure by plain solvent evaporation

Membranes with a hierarchical porous structure and an isoporous skin could be manufactured from a block copolymer blend by pure solvent evaporation (drying induced phase separation).

Artificial membranes with selective nanochannels for protein transport

Membranes based on poly(styrene-b-4-hydroxystyrene-b-styrene) were prepared with nanochannels for preferential transport of proteins with molecular weight 14.3 kg mol⁻¹ and rejection of neutral polyethylene glycol molecules with molecular size of 10 kg mol⁻¹.

Properties of some azo-copolyimide thin films used in the formation of photoinduced surface relief gratings

The patterning of the free standing azo-copolyimide films under different irradiation conditions led to the uniform surface relief gratings.

Thermal, dynamic mechanical, and dielectric analyses of some polyurethane biocomposites

Polymer biocomposites based on segmented poly(ester urethane) and extracellular matrix components have been prepared for the development of tissue engineering applications with improved biological characteristics of the materials in contact with blood and tissues for long periods. Thermal, dynamical, and dielectrical analyses were employed to study the molecular dynamics of these materials and the influence of changing the physical network morphology and hydrogen bond interactions accompanied by phase transitions, interfacial effects, and polarization or conductivity. All phenomena that concur in the tested materials are evaluated by cross-examination of the dynamic mechanical characteristic properties (storage modulus, loss modulus, and loss factor) and dielectric properties (relative permittivity, relative loss factor, and loss tangent) as a function of temperature. Comparative aspects were elucidated by calculating the apparent activation energies of multiplex experiments.

Pitfalls in diagnosis of primary low-grade non-Hodgkin’s lymphomas of the spleen

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Background: Primary low-grade (LG) non-Hodgkin’s lymphomas (NHL) of the spleen are indolent B-cell malignancies usually involving the liver, bone marrow (BM) and the blood while disseminating. The aim of the study was to outline diagnostic problems in primary LG NHL of the spleen, and to improve recommendations regarding the differential diagnosis between these lymphoproliferative disorders and benign abdominal organ pathology (BAOP). Methods: A series of 105 patients (pts) (age range of 15–82 years) with LG splenic NHL was enrolled in our study. In all pts the diagnosis was confirmed morphologically, with immunophenotyping in selected cases. The following histological types of splenic NHL had been identified: follicular (47.6%), small lymphocytic (37.1%), marginal-zone (11.4%), and mantle cell (3.9%) lymphoma. BM involvement and leukemic conversion (LC) were revealed at diagnosis in 102 (99.0%) and 85 (83.3%) pts, respectively. Results: Leading to diagnosis symptoms resulted from splenomegaly and hematological abnormalities. Of 41 (39.0%) pts with splenic NHL, that one had been initially interpreted and treated as chronic hepatitis with hypersplenism (17/16.2%), liver cirrhosis with portal hypertension and hypersplenism (11/10.5%), gastric ulcer/chronic gastroduodenitis (4/3.8%), chronic pancreatitis (3/2.9%), collagenosis (3/2.9%), or nephritis (1/0.9%). In 12 pts with a preliminary diagnosis of chronic hepatitis, or liver cirrhosis with portal hypertension and hypersplenism splenectomy was performed at the surgical departments of district hospitals as a treatment modality of choice. In these cases the initial histological examination of spleen specimens had failed to reveal the lymphomatous involvement, that led to delay in diagnosis. In 17 (16.2%) pts with stage IV disease LG splenic NHL was confirmed occasionally during prophylaxis follow up, or examinations axed on diagnosis of internal diseases. Conclusions: Primary LG NHL of the spleen exhibit the latent onset and nonspecific clinical picture, that usually lead to delay in diagnosis due to resemblance with BAOP. Progressive splenomegaly, LC, consequent liver, abdominal and peripheral lymph node enlargement may indicate the lymphoproliferative malignancy and require BM aspiration/biopsy for diagnosis.

No significant financial relationships to disclose.