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.

Hydrophobic polyamide nanofilms provide rapid transport for crude oil separation.

Hydrocarbon separation relies on energy-intensive distillation. Membrane technology can offer an energy-efficient alternative but requires selective differentiation of crude oil molecules with rapid liquid transport. We synthesized multiblock oligomer amines, which comprised a central amine segment with two hydrophobic oligomer blocks, and used them to fabricate hydrophobic polyamide nanofilms by interfacial polymerization from self-assembled vesicles. These polyamide nanofilms provide transport of hydrophobic liquids more than 100 times faster than that of conventional hydrophilic counterparts. In the fractionation of light crude oil, manipulation of the film thickness down to ~10 nanometers achieves permeance one order of magnitude higher than that of current state-of-the-art hydrophobic membranes while retaining comparable size- and class-based separation. This high permeance can markedly reduce plant footprint, which expands the potential for using membranes made of ultrathin nanofilms in crude oil fractionation.

Polytriazole membranes with ultrathin tunable selective layer for crude oil fractionation.

The design of materials and their manufacture into membranes that can handle industrial conditions and separate complex nonaqueous mixtures are challenging. We report a versatile strategy to fabricate polytriazole membranes with 10-nanometer-thin selective layers containing subnanometer channels for the separation of hydrocarbons. The process involves the use of the classical nonsolvent-induced phase separation method and thermal cross-linking. The membrane selectivity can be tuned to the lower end of the typical nanofiltration range (200 to 1000 gram mole-1). The polytriazole membrane can enrich up to 80 to 95% of the hydrocarbon content with less than 10 carbon atoms (140 gram mole-1). These membranes preferentially separate paraffin over aromatic components, making them suitable for integration in hybrid distillation systems for crude oil fractionation.

Tunable membranes incorporating artificial water channels for high-performance brackish/low-salinity water reverse osmosis desalination.

Membrane-based technologies have a tremendous role in water purification and desalination. Inspired by biological proteins, artificial water channels (AWCs) have been proposed to overcome the permeability/selectivity trade-off of desalination processes. Promising strategies exploiting the AWC with angstrom-scale selectivity have revealed their impressive performances when embedded in bilayer membranes. Herein, we demonstrate that self-assembled imidazole-quartet (I-quartet) AWCs are macroscopically incorporated within industrially relevant reverse osmosis membranes. In particular, we explore the best combination between I-quartet AWC and m-phenylenediamine (MPD) monomer to achieve a seamless incorporation of AWC in a defect-free polyamide membrane. The performance of the membranes is evaluated by cross-flow filtration under real reverse osmosis conditions (15 to 20 bar of applied pressure) by filtration of brackish feed streams. The optimized bioinspired membranes achieve an unprecedented improvement, resulting in more than twice (up to 6.9 L⋅m-2⋅h-1⋅bar-1) water permeance of analogous commercial membranes, while maintaining excellent NaCl rejection (>99.5%). They show also excellent performance in the purification of low-salinity water under low-pressure conditions (6 bar of applied pressure) with fluxes up to 35 L⋅m-2⋅h-1 and 97.5 to 99.3% observed rejection.

Naturally Extracted Hydrophobic Solvent and Self-Assembly in Interfacial Polymerization.

Pharmaceutical, chemical, and food industries are actively implementing membrane nanofiltration modules in their processes to separate valuable products and recover solvents. Interfacial polymerization (IP) is the most widely used method to produce thin-film composite membranes for nanofiltration and reverse osmosis processes. Although membrane processes are considered green and environmentally friendly, membrane fabrication has still to be further developed in such direction. For instance, the emission of volatile solvents during membrane production in the industry has to be carefully controlled for health reasons. Greener solvents are being proposed for phase-separation membrane manufacture. For the IP organic phase, the proposition of greener alternatives is in an early stage. In this work, we demonstrate the preparation of a high-performing composite membrane employing zero vapor pressure and naturally extracted oleic acid as the IP organic phase. Its long hydrophobic chain ensures intrinsic low volatility and acid monomer dissolution, while the polar head induces a unique self-assembly structure during the film formation. Membranes prepared by this technique were selective for small molecules with a molecular weight cutoff of 650 g mol-1 and a high permeance of ∼57 L m-2 h-1 bar-1.

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 ß 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.

Microfluidic Integrated Organic Electrochemical Transistor with a Nanoporous Membrane for Amyloid-ß Detection.

Alzheimer's disease (AD) is a neurodegenerative disorder associated with a severe loss in thinking, learning, and memory functions of the brain. To date, no specific treatment has been proven to cure AD, with the early diagnosis being vital for mitigating symptoms. A common pathological change found in AD-affected brains is the accumulation of a protein named amyloid-ß (Aß) into plaques. In this work, we developed a micron-scale organic electrochemical transistor (OECT) integrated with a microfluidic platform for the label-free detection of Aß aggregates in human serum. The OECT channel-electrolyte interface was covered with a nanoporous membrane functionalized with Congo red (CR) molecules showing a strong affinity for Aß aggregates. Each aggregate binding to the CR-membrane modulated the vertical ion flow toward the channel, changing the transistor characteristics. Thus, the device performance was not limited by the solution ionic strength nor did it rely on Faradaic reactions or conformational changes of bioreceptors. The high transconductance of the OECT, the precise porosity of the membrane, and the compactness endowed by the microfluidic enabled the Aß aggregate detection over eight orders of magnitude wide concentration range (femtomolar-nanomolar) in 1 µL of human serum samples. We expanded the operation modes of our transistors using different channel materials and found that the accumulation-mode OECTs displayed the lowest power consumption and highest sensitivities. Ultimately, these robust, low-power, sensitive, and miniaturized microfluidic sensors helped to develop point-of-care tools for the early diagnosis of AD.

Biomimetic artificial water channel membranes for enhanced desalination.

Inspired by biological proteins, artificial water channels (AWCs) can be used to overcome the performances of traditional desalination membranes. Their rational incorporation in composite polyamide provides an example of biomimetic membranes applied under representative reverse osmosis desalination conditions with an intrinsically high water-to-salt permeability ratio. The hybrid polyamide presents larger voids and seamlessly incorporates I-quartet AWCs for highly selective transport of water. These biomimetic membranes can be easily scaled for industrial standards (>m2), provide 99.5% rejection of NaCl or 91.4% rejection of boron, with a water flux of 75 l m-2 h-1 at 65 bar and 35,000 ppm NaCl feed solution, representative of seawater desalination. This flux is more than 75% higher than that observed with current state-of-the-art membranes with equivalent solute rejection, translating into an equivalent reduction of the membrane area for the same water output and a roughly 12% reduction of the required energy for desalination.

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.

Carboxyl-functionalized nanochannels based on block copolymer hierarchical structures.

When building artificial nanochannels, having a scalable robust platform with controlled morphology is important, as well as having the option for final functionalization of the channels for the selective transport of water and proteins. We have previously developed asymmetric membranes that have a surface layer of very sharp pore size distribution, surface charge and pore functionalization. Here, a more complex bioinspired platform is reported. Hierarchical isotropic porous structures with spherical micrometer-sized cavities, interconnected by hexagonally ordered nanochannels, were prepared based on the phase separation of polystyrene-b-poly(t-butyl acrylate) block copolymers, following a nucleation and growth mechanism. The structure was imaged by scanning electron microscopy, which demonstrated a high density of ordered nanochannels. The hexagonal order formed by the self-assembly in solution was confirmed by small-angle X-ray scattering. The structure evolution was investigated by time-resolved grazing-incidence small-angle X-ray scattering. The assembled hydrophobic hierarchical structure was then converted to a hydrophilic structure by acid hydrolysis, leading to nanochannels covered by carboxylic groups and therefore convenient for water transport.

Artificial 3D hierarchical and isotropic porous polymeric materials.

Hierarchical porous materials that replicate complex living structures are attractive for a wide variety of applications, ranging from storage and catalysis to biological and artificial systems. However, the preparation of structures with a high level of complexity and long-range order at the mesoscale and microscale is challenging. We report a simple, nonextractive, and nonreactive method used to prepare three-dimensional porous materials that mimic biological systems such as marine skeletons and honeycombs. This method exploits the concurrent occurrence of the self-assembly of block copolymers in solution and macrophase separation by nucleation and growth. We obtained a long-range order of micrometer-sized compartments. These compartments are interconnected by ordered cylindrical nanochannels. The new approach is demonstrated using polystyrene-b-poly(t-butyl acrylate), which can be further explored for a broad range of applications, such as air purification filters for viruses and pollution particle removal or growth of bioinspired materials for bone regeneration.

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.

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.