Interesting Class Of Materials Research Articles

Simulation and Experimental Study of the Isothermal Thermogravimetric Analysis and the Apparent Alterations of the Thermal Stability of Composite Polymers.

Composite polymers are an interesting class of materials with a wide range of applications. Among the properties of polymers which are currently being enhanced via the development of composite materials is their thermal stability, which is typically evaluated via thermogravimetric analysis (TGA). In this work, a paradox is recognized regarding the considered relationship between the polymer-filler interactions leading to a good dispersion of the filler and the improvement of thermal stability. Simulation of the TGA signal during isothermal measurements of composite polymers is performed along with experimental measurements. It is shown that there are at least three factors that can cause apparent alterations of the thermal stability of composite polymers, namely, the different buoyancy due to the different densities of the composites and the neat polymer, the different thermal diffusivity of the composites and the fact that the mass loss (or remaining mass) of the composites, conventionally, is expressed per overall mass of the composite and not per mass of polymer. The relative contributions of these factors are evaluated and it is found that the conventional expression of mass loss has the most profound effect. Furthermore, it is shown that it is proper to express and evaluate the TGA results of composite polymers per degradable (polymer) mass of the composite and not per overall mass of the composite.

Magnetism and fermiology of kagome magnet YMn6Sn4Ge2

Kagome lattice magnets are an interesting class of materials as they can host topological properties in their magnetic and electronic structures. YMn6Sn6 is one such compound in which various exotic magnetic and electronic topological properties have been realized. Here, by means of a partial substitution of Sn with an isovalent and slightly smaller atom Ge, we demonstrate the sensitivity of such chemical substitution on the magnetic structure and its influence in the electronic properties. Magnetic structure of YMn6Sn4Ge2 determined by neutron diffraction reveals an incommensurate staggered magnetic spiral with a slightly larger spiral pitch than in YMn6Sn6. This change in magnetic structure influences the Fermi surface enhancing the out-of-plane conductivity. Such a sensitivity to the partial chemical substitution provides a great potential for engineering the magnetic phases and associated electronic properties not only in YMn6Sn6, but also in the large family of 166 rare-earth kagome magnet.

Lamellar structure formed from block copolymer for structural color

Certain brilliant colors in living species, such as, in plants, animals, insects, fungi, seaweed, and so on, known as structural colors, have attracted tremendous attention from researchers worldwide. Block copolymers are an interesting class of material that has been proven effective in fabricating structural colors due to their capability to self-assemble into structures on the scale of the wavelength of visible light. Lamellar structure is one of these structures. The demand on the high-quality structural colors in large scale application requires the easy modification of commercial block copolymers to obtain structural colors. In this project, a method to easily prepare structural colors is presented. First, an already commercialized block polymer was purchased. Then, the block copolymer is mixed with the small molecule guest to prepare a supramolecular complex solution. By slowly evaporating the solution, these supramolecular complexes can be assembled into a lamellar structure that displays structural color. By changing the ratio of polymer to small molecular guest and using different small molecular guests, polymer films of different colors can be obtained and tuned.

Nature of Dielectric Response of Phenyl Alcohols.

Phenyl alcohols (PhAs) are an interesting class of materials, for which the dielectric response reveals only the presence of single prominent Debye-like (D) relaxation, interpreted as a genuine structural (α) process. Herein, we have performed dielectric and mechanical measurements on a series of PhAs characterized by the varying length of the alkyl chain and found that this interpretation is not valid. Analysis of the derivative of the real part of the complex permittivity together with the mechanical and light scattering data clearly indicated that the prominent dielectric D-like peak is actually a superposition of both cross-correlation between dipole-dipole (D-mode) and self-dipole correlation (α-process) and that the distinguished α-mode exhibits a similar ("generic") shape of PhAs independently to their molecular weight and applied experimental technique. Therefore, the data presented herein contribute to the whole discussion focused on the dielectric response function and universality (or diversity) of the spectral shape of the α-mode of polar liquids.

Polynitrogen High Energy Density Materials Synthesized by Nonequilibrium Plasma

Metal pentazolate compounds that contain 5-nitrogen singly charged anion rings are an interesting class of materials from a thermodynamics perspective. These compounds are believed to be equilibrium phases only at extremely high pressures, and thus, they constitute exotic states of matter at ambient pressure and temperature. Moreover, the energy released by these pentazolate compounds upon relaxation to the equilibrium state at ambient conditions is in the range 1 to 10 MJ per kg, rivaling that of combustion reactions. The synthesis of pentazolates is not an easy task, and there are only two known methods, each of which has significant challenges. The development of new scalable synthesis routes could enable the production of these exotic materials in sufficient quantity to explore their properties more widely beyond the context of explosives and propellants. In this Perspective, it is argued that nonequilibrium plasma is a promising reaction medium for the synthesis of metal pentazolate compounds, for example from the corresponding metal azide and N2 gas activated by the discharge at low background temperature.

In-situ Neutron Reflectometry to Determine Ge Self-Diffusivities and Activation Energy of Diffusion in Amorphous Ge0.8Si0.2

Amorphous Ge-Si solid solutions are an interesting class of materials from the fundamental as well as the technological point of view. Self-diffusion of the constituents is an important process because of the inherent metastability. While self-diffusion was already examined in crystalline GexSi1-x (0 < x <1) this is not the case for the amorphous counterparts. This work reports on Ge self-diffusivities obtained from insitu neutron reflectometry measurements during isothermal annealing of ion-beam sputter-deposited amorphous Ge0.8Si0.2 films. The diffusivities are modified peculiarly fast with annealing time by a maximum factor of two due to structural relaxation. The diffusivities in the relaxed state are lower (higher) than in amorphous germanium (silicon). They follow the Arrhenius law and show an activation energy of (2.06 ± 0.1) eV, which equals that of amorphous germanium, but differs from that of amorphous silicon. Thus, it is concluded that the diffusion mechanism of Ge in amorphous Ge0.8Si0.2 and Ge are similar, despite of the presence of dispersed 20 at.% of Si.

Physico-Chemical Properties and Principal Component Analysis of Biobased Thermosets Developed with Different Batches of Industrial Humins.

Humins have already shown their potential as thermosetting resins to produce crosslinked networks and composites, with a large variety of properties depending on the used macromolecular approach. Our group has shown that a very interesting class of materials with tunable flexibility can be made by humins co-polymerization with glycerol diglycidyl ether (GDE). To create a clearer picture on structure-reactivity-properties-application interdependent relationship, a principal component analysis (PCA) was applied on several humins batches. The PCA allowed to obtain a clear discrimination between the humins/GDE resins samples in 3 groups which correlate very well with the results of copolymerization reactivity (DSC) and thermosets properties: crosslink density, thermal stability, tan δ, Shore D hardness values, etc.

Scattering-type Scanning Near-Field Optical Microscopy of Polymer-Coated Gold Nanoparticles.

Scattering-type scanning near-field optical microscopy (s-SNOM) has emerged over the past years as a powerful characterization tool that can probe important properties of advanced materials and biological samples in a label-free manner, with spatial resolutions lying in the nanoscale realm. In this work, we explore such usefulness in relationship with an interesting class of materials: polymer-coated gold nanoparticles (NPs). As thoroughly discussed in recent works, the interplay between the Au core and the polymeric shell has been found to be important in many applications devoted to biomedicine. We investigate bare Au NPs next to polystyrenesulfonate (PSS) and poly(diallyldimethylammonium chloride) (PDDA) coated ones under 532 nm laser excitation, an wavelength matching the surface plasmon band of the custom-synthesized nanoparticles. We observe consistent s-SNOM phase signals in the case of bare and shallow-coated Au NPs, whereas for thicker shell instances, these signals fade. For all investigated samples, the s-SNOM amplitude signals were found to be very weak, which may be related to reduced scattering efficiency due to absorption of the incident beam. We consider these observations important, as they may facilitate studies and applications in nanomedicine and nanotechnology where the precise positioning of polymer-coated Au NPs with nanoscale resolution is needed besides their dielectric function and related intrinsic optical properties, which are also quantitatively available with s-SNOM.

Tunable Cytotoxicity and Selectivity of Phosphonium Ionic Liquid with Aniline Blue Dye.

Ionic liquids are an interesting class of materials that have recently been utilized as chemotherapeutic agents in cancer therapy. Aniline blue, a commonly used biological staining agent, was used as a counter ion to trihexyltetradecylphosphonium, a known cytotoxic cation. A facile, single step ion exchange reaction was performed to synthesize a fluorescent ionic liquid, trihexyltetradecylphosphonium aniline blue. Aqueous nanoparticles of this hydrophobic ionic liquid were prepared using reprecipitationmethod. The newly synthesized ionic liquid and subsequent nanoparticles were characterized using various spectroscopic techniques. Transmission electron microscopy and zeta potential measurements were performed to characterize the nanoparticles' morphology and surface charge. The photophysical properties of the nanoparticles and the parent aniline blue compound were studied using absorption and fluorescence spectroscopy. Cell viability studies were conducted to investigate the cytotoxicity of the newly developed trihexyltetradecylphosphonium aniline blue nanoparticles in human breast epithelial cancer cell line (MCF-7) and its corresponding normal epithelial cell line (MCF-10A) in vitro. The results revealed that the synthesized ionic nanomedicines were more cytotoxic (lower IC50) than the parent chemotherapeutic compound in MCF-7 cells. Nanoparticles of the synthesized ionic liquid were also shown to be more stable in both aqueous and cellular media and more selective than parent compounds towards cancer cells.

Tailoring Therapeutic Responses via Engineering Microenvironments with a Novel Synthetic Fluid Gel.

This study reports the first fully synthetic fluid gel (SyMGels) using a simple poly(ethylene glycol) polymer. Fluid gels are an interesting class of materials: structured during gelation via shear-confinement to form microparticulate suspensions, through a bottom-up approach. Structuring in this way, when compared to first forming a gel and subsequently breaking it down, results in the formation of a particulate dispersion with particles "grown" in the shear flow. Resultantly, systems form a complex microstructure, where gelled particles concentrate remaining non-gelled polymer within the continuous phase, creating an amorphous-like interstitial phase. As such, these materials demonstrate mechanical characteristics typical of colloidal glasses, presenting solid-like behaviors at rest with defined yielding; likely through intrinsic particle-particle and particle-polymer interactions. To date, fluid gels have been fabricated using polysaccharides with relatively complex chemistries, making further modifications challenging. SyMGels are easily functionalised, using simple click-chemistry. This chemical flexibility, allows the creation of microenvironments with discrete biological decoration. Cellular control is demonstrated using MSC (mesenchymal stem cells)/chondrocytes and enables the regulation of key biomarkers such as aggrecan and SOX9. These potential therapeutic platforms demonstrate an important advancement in the biomaterial field, underpinning the mechanisms which drive their mechanical properties, and providing a versatile delivery system for advanced therapeutics.

Facile synthesis of highly biologically active chitosan functionalized 2D WS2 nanocomposite anchored with palladium nanoparticles for antibacterial and anticancer activity: In-vitro biomedical evaluation

Since the discovery of graphene, the curiosity in two-dimensional (2D) nanomaterials grew significantly. Among the numerous 2D nanomaterials, the transition metal dichalcogenides (TMDCs) received significant interest from the scientific world. TMDCs such as MoS2 and WS2 are new and an interesting class of materials, and show considerable promise for use in a wide variety of fields, including nanomedicine for cancer. The multi-component drug delivery system has now become a popular hub in cancer science. The WS2 nanosheet was preferred as the raw material in this research, it functionalized in addition to chitosan and palladium (CS/WS2/Pd). Hence, we studied the impact of this material on antibacterial and anticancer activity. The antibacterial efficacy of CS/WS2/Pd composite is then investigated against very dangerous bacteria such as Gram-positive (Bacillus subtilis, Staphylococcus aureus), and Gram-negative (Klebsiella pneumoniae, Escherichia coli). The CS/WS2/Pd composite was designed to have significant antibacterial activity against E. coli bacteria than B. subtilis, S. aureus, and K. pneumoniae). The CS/WS2/Pd composite exhibits 73.24% cell inhibition against MCF-7 breast cancer cells. These findings anticipated that this new 2D inorganic group would play a crucial role in the next generation of cancer treatments.

Synthesis of hyperbranched Co-Ni-P nanocrystals and their splitting degree dependent HER performances

Hyperbranched transition metal phosphides (TMPs) nanocrystals are an interesting class of materials, which can be used as an efficient catalyst for hydrogen evolution reaction (HER). However, big challenge remains for the preparation of ternary hyperbranched TMPs, and relationship between their HER performances and the splitting degree is also not well understood. Here, hyperbranched Co-Ni-P nanocrystals with different splitting degrees were prepared via a novel strategy, and their alkaline HER performances were studied. During the synthesis process, hyperbranched Co2P nanocrystals were used as template, and Ni precursors were injected into the reaction solution at different holding stage. When the Ni precursor was injected earlier, the podgy particles with low splitting degree would be obtained. Conversely, delaying the injection of Ni precursor would lead to high splitting degree. The formation process of ternary phase was also studied. After Ni precursor was injected, a Co-Ni-P amorphous layer was formed on the surface of the Co2P particles, and then the Ni atoms diffused into the Co2P phase to form Co-Ni-P nanocrystals. Electrochemical performances tests show that the splitting degree has great impact on HER performances. The higher splitting degree usually leads to larger electrochemical surface area, and higher catalytic activity can be achieved. The sheaf-like Co-Ni-P nanocrystals demonstrate a small overpotential of 119 mV at current density of 10 mA cm−2, and good durability over 23 h in 1 M KOH solution. We believe that this work can help understand the relationship between the HER performances of hyperbranched TMPs nanocrystals and their splitting degree, and provide a synthetic strategy for the preparation of highly efficient TMPs catalysts.

Oxygenation of conducting polymers facilitated by structure‐breaking anions

AbstractConducting polymers are an interesting class of materials that can be tuned to have a range of properties through counterion doping. For most conducting polymers, the insertion of anions (the doping process) leads to the formation of carbocations (positive charge carriers) along the conjugated polymer backbone. In this research, we report on a scenario that arises where certain (commonly used) anions in water induce oxygenation of the conducting polymers heteroatom. This is in contrast to the widely reported doping process, and the recently reported hydrolysis of conducting polymers. We observe that the transition between these different conducting polymer‐interactions/reactions is well described by the concept of structure‐making and structure‐breaking anions. Poly(3,4‐propylenedioxy thiophene dimethyl) (PProDOT‐Me2), polypyrrole (PPy), and poly(3,4‐ethylenedioxy thiophene) (PEDOT) thin films are exposed to a range of anions in water. Both PProDOT‐Me2 and PPy are susceptible to oxygenation, while in contrast PEDOT is doped, when exposed to structure‐breaking anions. All the polymers show hydrolysis for structure‐making anions. The knowledge of the interaction and/or reaction of conducting polymers with anions in water is not only critical to their application in devices for aqueous environments (i.e., sensing), but also for their processing and fabrication using water.

Synthesis of biocompatible chitosan functionalized Ag decorated biocomposite for effective antibacterial and anticancer activity

The transition-metal dichalcogenides (TMDCs) like MoS2 and WS2 are a new and interesting class of materials and show considerable promise for use in a wide variety of fields, including nanomedicine for cancer. The eco-friendly, biodegradability, toxicity, and antimicrobial activity remain an open issue. Herein, we focused on the current demands of two dimensional (2D) TMDCs and produced high-quality, few-layered MoS2 nanosheets. Noble metal Ag incorporated into the 2D-CS/MoS2 NC by the liquid exfoliated process. The manufactured CS/MoS2/Ag hybrid NC showed excellent antibacterial activity against two microorganisms such as Gram-positive (21, 27, and 33 mm) and Gram-negative bacteria (23, 30, and 39 mm). The CS/MoS2/Ag hybrid NC was designed to have significant antibacterial activity against E.coli bacteria than S.aureus. Furthermore, the hybrid NC has a 74.18% cell inhibition against MCF-7 cancer cells. According to the literature relevant, it is the first extensive experimental analysis on the nano-bio interaction of 2D TMDCs nanomaterials in MCF-7 breast cancer cells.

Long-range ordering of two-dimensional wide bandgap tantalum oxide nanosheets in printed films.

Two-dimensional oxide materials are a well-studied, interesting class of materials, enabled by the fact that their bulk layered metal oxides, such as titanates and niobates, can be easily exfoliated within minutes into 2D nanosheets. However, some promising oxide materials, such tantalum oxide, are much more difficult to delaminate, taking several weeks, due to the higher charge density resulting in stronger Coulombic interactions between the layers. This intrinsic constraint has limited detailed studies for exploiting the promising properties of tantalum oxide 2D nanosheets towards enhanced catalysis and energy storage. Here, we have studied in detail the exfoliation mechanism of high charge density 2D materials, specifically tantalum oxide (TaO3) nanosheets. Optimization of tetrabutylphosphonium hydroxide (TBPOH) as the exfoliation agent in a 2 : 1 ratio to HTaO3 has resulted in a dramatic reduction of the exfoliation time down to only 36 hours at 80 °C. Furthermore, single monolayers of TaO3 nanosheets with >95% coverage have been achieved by Langmuir–Blodgett deposition, while thicker layers (ranging from several tens of nanometers up to microns) exhibiting long-range ordering of the present nanosheets have been realized through inkjet printing. Interestingly, scanning tunneling microscopy analysis indicated a wide bandgap of ∼5 eV for the single TaO3 nanosheets. This value is significantly higher than the reported values between 3.5 and 4.3 eV for the layered RbTaO3 parent compound, and opens up new opportunities for 2D oxide materials.

Simultaneous observation of anti-damping and the inverse spin Hall effect in the La0.67Sr0.33MnO3/Pt bilayer system.

Manganites have shown potential in spintronics because they exhibit high spin polarization. Here, by ferromagnetic resonance we have studied the damping properties of La0.67Sr0.33MnO3/Pt bilayers which are prepared by oxide molecular beam epitaxy. The damping coefficient (α) of a La0.67Sr0.33MnO3 (LSMO) single layer is found to be 0.0104. However the LSMO/Pt bilayers exhibit a decrease in α with an increase in Pt thickness. This decrease in the value of α is probably due to high anti-damping like torque. Furthermore, we have investigated the angle dependent inverse spin Hall effect (ISHE) to quantify the spin pumping voltage from other spin rectification effects such as the anomalous Hall effect and anisotropic magnetoresistance. We have observed a high spin pumping voltage (∼20 μV). The results indicate that both anti-damping and spin pumping phenomena occur simultaneously.

Expanding the Chemistry of Salt-Inclusion Materials: Utilizing the Titanyl Ion as a Structure Directing Agent for the Targeted Synthesis of Salt-Inclusion Titanium Silicates

Salt-Inclusion Materials (SIMs) are a diverse and interesting class of materials. However, their synthesis has been largely serendipitous. The targeted synthesis of SIMs requires both synthetic and...

Trends in elastic properties of Ti–Ta alloys from first-principles calculations

The martensitic start temperature (M s) is a technologically fundamental characteristic of high-temperature shape memory alloys. We have recently shown [Chakraborty et al 2016 Phys. Rev. B 94 224104] that the two key features in describing the composition dependence of M s are the T = 0 K phase stability and the difference in vibrational entropy which, within the Debye model, is directly linked to the elastic properties. Here, we use density functional theory together with special quasi-random structures to study the elastic properties of disordered martensite and austenite Ti–Ta alloys as a function of composition. We observe a softening in the tetragonal shear elastic constant of the austenite phase at low Ta content and a non-linear behavior in the shear elastic constant of the martensite. A minimum of 12.5% Ta is required to stabilize the austenite phase at T = 0 K. Further, the shear elastic constants and Young’s modulus of martensite exhibit a maximum for Ta concentrations close to 30%. Phenomenological, elastic-constant-based criteria suggest that the addition of Ta enhances the strength, but reduces the ductile character of the alloys. In addition, the directional elastic stiffness, calculated for both martensite and austenite, becomes more isotropic with increasing Ta content. The reported trends in elastic properties as a function of composition may serve as a guide in the design of alloys with optimized properties in this interesting class of materials.

Current methodologies and approaches for the formation of core–sheath polymer fibers for biomedical applications

The application of polymer fibers has rocketed to unimaginable heights in recent years and occupies every corner of our day-to-day life, from knitted protective textile clothes to buzzing smartphone electronics. Polymer fibers could be obtained from natural and synthetic polymers at a length scale from the nanometer to micrometer range. These fibers could be formed into different configurations such as single, core–sheath, hollow, blended, or composite according to human needs. Of these several conformations of fibers, core–sheath polymer fibers are an interesting class of materials, which shows superior physical, chemical, and biological properties. In core–sheath fiber structures, one of the components called a core is fully surrounded by the second component known as a sheath. In this format, different polymers can be applied as a sheath over a solid core of another polymer, thus resulting in a variety of modified properties while maintaining the major fiber property. After a brief introduction to core–sheath fibers, this review paper focuses on the development of the electrospinning process to manufacture core–sheath fibers followed by illustrating the current methodology and approaches to form them on a larger scale, suitable for industrial manufacturing and exploitation. Finally, the paper reviews the applications of the core–sheath fibers, in particular, recent studies of core–sheath polymer fibers in tissue engineering (nerve, vascular grafts, cardiomyocytes, bone, tendons, sutures, and wound healing), growth factors and other bioactive component release, and drug delivery. Therefore, core–sheath structures are a revolutionary development in the field of science and technology, becoming a backbone to many emerging technologies and novel opportunities.

Stability of epitaxial BiXO3 phases by density-functional theory

The bismuth-based perovskites are an interesting class of materials that exhibit a variety of coupled ferroic properties. Through epitaxial growth in the (001) pseudo-cubic [(001)pc] orientation, various phases with variable ferroelectric polarization can be stabilized. Using density-functional theory calculations, we predict the phase stability of the bismuth-based perovskite oxides as a function of pseudo-cubic in-plane (IP) lattice constant, mimicking (001)pc epitaxial films. We find that the BiMnO3, BiCoO3, and BiNiO3 systems each exhibit only one stable phase over a wide range of IP lattice constants. In the BiFeO3 (BFO) and BiCrO3 (BCO) systems, by comparison, we find several phases that are energetically favorable, depending on the value of the IP strain. The BFO phases predicted to be stable, in order of increasing compressive IP strain, are monoclinic Cc, triclinic P1, monoclinic Cm, and tetragonal P4mm. In the BCO system, we find two orthorhombic Pbnm phases, respectively, under no IP strain and under compressive IP strain, and one monoclinic Cc phase to be stable under tensile IP strain. Our results serve to guide experimental efforts in terms of selecting growth substrates with the goal of achieving desired epitaxial-stabilized perovskite phases and to support future investigations of the tunability of BXO properties with epitaxial strain.