Interest For Many Applications Research Articles

POSS-embedded supramolecular hyperbranched polymers constructed from a 1→7 branching monomer with controllable morphology transitions

The research on the supramolecular hyperbranched polymers (SHPs) that combines the advantages of supramolecular polymer and hyperbranched architecture has attracted considerable interests in many applications. Here we demonstrate a simple approach to prepare POSS-embedded supramolecular hyperbranched polymers (POSS-SHPs) with varied morphology and size by controlling monomer concentration and mixed solvents. The SHPs formations can further transfer into the core-shell structured micelles by addition of competitive guests based on the double supramolecular driving forces.

A review on mechanical and water absorption properties of polyvinyl alcohol based composites/films

AbstractPolyvinyl alcohol (PVA) is a nontoxic and thermoplastic polymer which is completely biodegradable. PVA shows excellent mechanical and thermal properties due to better interfacial adhesion with reinforcing material such as fibers, particles or flakes because of which it can be used for fabrication of composite. PVA based fiber or particle reinforcing composites have gained interest in many applications in different fields. This paper reviews the mechanical and water absorption properties studied by different researcher and some of them were discussed here. The article also focused on the effect on the mechanical properties on PVA based composites with particle or fiber used as reinforcing material at nano/micro level and different polymers used to prepare PVA blend films. The major disadvantage of PVA based composites/films is higher water uptake or solubility in water. To over this negative aspect, many researchers studied crosslinking of PVA based composites/films, which are also discussed in the article. This review concludes that PVA has the potential for use in the synthesis of composites/films with their abundant applications.

An organic silver complex conductive ink using both decomposition and self-reduction mechanisms in film formation

Flexible electronics is of considerable interest for many applications due to the distinctive features of low-cost, flexibility and light weight capabilities. However, in translating the technology from research to practical applications one faces many challenges. One of them is to formulate suitable ink materials where the selection of functional components, for example in the case of organic silver ink, the silver precursor, complexing agent and volatile organic solvent, are very critical because these constituents determine the final properties of the ink. In this paper, a new type of silver organic ink with decomposition and self-reduction mechanisms (10 wt% silver content) was formulated. It is shown that the ink is capable of producing silver films with good uniformity and conductivity on a polyimide substrate after sintering at 155 °C. The effect of solvent on the thermal property of the formulated ink have been investigated by differential scanning calorimetry (DSC) and UV–Vis spectrscopy, where the active roles of the solvents and the underlying chemical reactions in the ink during heating were studied. The reaction mechanism between the complexing agent and the silver precursor was confirmed by FT-IR measurements. The effects of sintering temperature and time on the microstructure and electrical properties of the silver ink films have been studied in detail using XRD, SEM/EDX and 4-probe based techniques. The defects such as voids and cracks as well as the coffee rings, which are often associated with films produced from organic silver inks, were reduced significantly by using both decomposition and self-reduction mechanisms in film formation.

Transparent, abrasion-insensitive superhydrophobic coatings for real-world applications

Superhydrophobic surfaces and surface coatings are of high interest for many applications in everyday life including non-wetting and low-friction coatings as well as functional clothing. Manufacturing of these surfaces is intricate since superhydrophobicity requires structuring of surfaces on a nano- to microscale. This delicate surface structuring makes most superhydrophobic surfaces very sensitive to abrasion and renders them impractical for real-life applications. In this paper we present a transparent fluorinated polymer foam that is synthesized by a simple one-step photoinitiated radical polymerization. We term this material “Fluoropor”. It possesses an inherent nano-/microstructure throughout the whole bulk material and is thus insensitive to abrasion as its superhydrophobic properties are not merely due to a thin-layer surface-effect. Due to its foam-like structure with pore sizes below the wavelength of visible light Fluoropor appears optically transparent. We determined contact angles, surface energy, wear resistance and Vickers hardness to highlight Fluoropor’s applicability for real-word applications.

Importance of film morphology on the performance of thermo-responsive waterborne pressure sensitive adhesives

Temperature responsive pressure sensitive adhesives (PSAs) are of interests in many applications due to the possibility of removing strong adhesives by moderate heating. In this work, semicrystalline poly(octadecyl acrylate) obtained by miniemulsion polymerization is used as a key component of the thermal responsiveness. Comparison of the adhesive performance of crystalline hard core-soft shell PSAs with other PSAs of the same overall composition and similar molar mass distributions but prepared by blending soft and hard latexes shows that the arrangement of the phases in the film play a key role in performance of the PSAs. Good adhesive performance and thermal responsiveness is only achieved when the crystalline domains are dispersed in a continuous soft phase containing entangled nanogels. Interestingly, this morphology is achieved with blends, but no with core-shell dispersions. The reasons for this difference are investigated.

Evolution of the shape of a high-current and moderate energy electron beam at its propagation through D2 at low pressure

The paper presents the experimental data on the time-spatial evolution of electron beam that is formed and propagates in a dielectric tube of large volume filled with D2 at low pressure of 1-2 Torr. The e-beam is generated by gas discharge in a short gap powered by the stepwise high voltage with amplitude up to 25 kV. Initially, this discharge appears in a strongly over-voltage regime which is unstable and eventually (in several hundreds of ns) transits into abnormal glow discharge at the voltage about of 1.5 - 2.5 kV and the current amplitude of several hundreds of Amps. The every of the mentioned discharge regimes generates the e-beam with energy up to 25 and 2.5 keV respectively. The ability of the over-voltage gap to generate the high- and low-energy e-beams happening one by one can be of great interest for many applications. The features in spatial structures of high-energy and low-energy e-beams in the course of their propagation over long distance through deuterium at low pressure are revealed and discussed.

Systematic design of active spaces for multi-reference calculations of singlet–triplet gaps of organic diradicals, with benchmarks against doubly electron-attached coupled-cluster data

Singlet-triplet gaps in diradical organic π-systems are of interest in many applications. In this study, we calculate them in a series of molecules, including cyclobutadiene and its derivatives and cyclopentadienyl cation, by using correlated participating orbitals within the complete active space (CAS) and restricted active space (RAS) self-consistent field frameworks, followed by second-order perturbation theory (CASPT2 and RASPT2). These calculations are evaluated by comparison with the results of doubly electron-attached (DEA) equation-of-motion (EOM) coupled-cluster (CC) calculations with up to 4-particle-2-hole (4p-2h) excitations. We find active spaces that can accurately reproduce the DEA-EOMCC(4p-2h) data while being small enough to be applicable to larger organic diradicals.

New FeMnSi+Al Alloy Proposed for High Damping Capacity Elements

High damping capacity materials present an increased interest in many applications were vibration and noise reduction is absolutely necessary. Metallic materials with a high internal friction (IF) are becoming valuable because of them usual mechanical properties that fulfill the damping capacity in applications. Some of the shape memory alloys present a huge damping capacity during the solid state transformation (M↔A) based on the re-orientation and accommodation of the material structure. Iron based shape memory alloy present the best advantages for industrial application as dumpers in different areas. Beside civil construction domain these materials can cover also applications in automotive industry as shock impact absorbers for low velocities as protection for engine parts and also for noise reduction. By these means in this article we analyze FeMnSi+Al alloy with a new chemical composition obtained through classical melting method in Ar controlled atmosphere.

Nanosecond pulsed humid Ar plasma jet in air: shielding, discharge characteristics and atomic hydrogen production

Gas phase non-equilibrium plasmas jets containing water vapor are of growing interest for many applications. In this manuscript, we report a detailed study of an atmospheric pressure nanosecond pulsed Ar + 0.26% H2O plasma jet.The plasma jet operates in an atmospheric pressure air surrounding but is shielded with a coaxial argon flow to limit the air diffusion into the jet effluent core. The jet impinges on a metal plate electrode and produces a stable plasma filament (transient spark) between the needle electrode in the jet and the metal plate. The stable plasma filament is characterized by spatially and time resolved electrical and optical diagnostics. This includes Rayleigh scattering, Stark broadening of the hydrogen Balmer lines and two-photon absorption laser induced fluorescence (TaLIF) to obtain the gas temperature, the electron density and the atomic hydrogen density respectively. Electron densities and atomic hydrogen densities up to and have been measured. This shows that atomic hydrogen is one of the main species in high density Ar-H2O plasmas. The gas temperature does not exceed 550 K in the core of the plasma.To enable in situ calibration of the H TaLIF at atmospheric pressure a previously published O density calibration scheme is extended to include a correction for the line profiles by including overlap integrals as required by H TaLIF. The line width of H TaLIF, due to collision broadening has the same trend as the neutral density obtained by Rayleigh scattering. This suggests the possibility to use this technique to in situ probe neutral gas densities.

Fixpoint semantics and optimization of recursive Datalog programs with aggregates

AbstractA very desirable Datalog extension investigated by many researchers in the last 30 years consists in allowing the use of the basic SQL aggregates min, max, count and sum in recursive rules. In this paper, we propose a simple comprehensive solution that extends the declarative least-fixpoint semantics of Horn Clauses, along with the optimization techniques used in the bottom-up implementation approach adopted by many Datalog systems. We start by identifying a large class of programs of great practical interest in which the use of min or max in recursive rules does not compromise the declarative fixpoint semantics of the programs using those rules. Then, we revisit the monotonic versions of count and sum aggregates proposed by Mazuran et al. (2013b, The VLDB Journal 22, 4, 471–493) and named, respectively, mcount and msum. Since mcount, and also msum on positive numbers, are monotonic in the lattice of set-containment, they preserve the fixpoint semantics of Horn Clauses. However, in many applications of practical interest, their use can lead to inefficiencies, that can be eliminated by combining them with max, whereby mcount and msum become the standard count and sum. Therefore, the semantics and optimization techniques of Datalog are extended to recursive programs with min, max, count and sum, making possible the advanced applications of superior performance and scalability demonstrated by BigDatalog (Shkapsky et al. 2016. In SIGMOD. ACM, 1135–1149) and Datalog-MC (Yang et al. 2017. The VLDB Journal 26, 2, 229–248).

Investigation of the impact of high liquid viscosity on jet atomization in crossflow via high-fidelity simulations

Atomization of extremely high viscosity liquid can be of interest for many applications in aerospace, automotive, pharmaceutical, and food industries. While detailed atomization measurements usually face grand challenges, high-fidelity numerical simulations offer the advantage to comprehensively explore the atomization details. In this work, a previously validated high-fidelity first-principle simulation code HiMIST is utilized to simulate high-viscosity liquid jet atomization in crossflow. The code is used to perform a parametric study of the atomization process in a wide range of Ohnesorge numbers (Oh = 0.004–2) and Weber numbers (We = 10–160). Direct comparisons between the present study and previously published low-viscosity jet in crossflow results are performed. The effects of viscous damping and slowing on jet penetration, liquid surface instabilities, ligament formation/breakup, and subsequent droplet formation are investigated. Complex variations in near-field and far-field jet penetrations with increasing Oh at different We are observed and linked with the underlying jet deformation and breakup physics. Transition in breakup regimes and increase in droplet size with increasing Oh are observed, mostly consistent with the literature reports. The detailed simulations elucidate a distinctive edge-ligament-breakup dominated process with long surviving ligaments for the higher Oh cases, as opposed to a two-stage edge-stripping/column-fracture process for the lower Oh counterparts. The trend of decreasing column deflection with increasing We is reversed as Oh increases. A predominantly unimodal droplet size distribution is predicted at higher Oh, in contrast to the bimodal distribution at lower Oh. It has been found that both Rayleigh-Taylor and Kelvin-Helmholtz linear stability theories cannot be easily applied to interpret the distinct edge breakup process and further study of the underlying physics is needed.

Redox-responsive polymers for anti-cancer drug delivery and bioimaging

Smart protein-mimetic materials have received increasing interest for many applications. Here, we reported a facile and efficient approach to prepare a class of dual-responsive copoly(l-glutamate)s by ring-opening polymerization (ROP) and post-modification strategy. Both the oligo(ethylene glycol) (OEG) and glutamic acid residues were incorporated to offer thermal- and pH-responsive property simultaneously. We present a systematic study of the influence of both temperature and pH on the solution properties of the copolypeptides. The copolypeptides show entirely reversible pH-dependent thermal-responsive behaviors with tunable phase transition temperatures. It is demonstrated that the sequence of the polymer units can also influence the solution behavior. The α-helix conformation appears to be the dominant secondary conformation, which shows the pH dependence, but generally irrespective of the temperature. We further verify that the reduced circular dichroism (CD) signal upon heating above the clouding point (CP) is entirely due to the aggregation of the polymer chains. All these features make the obtained polypeptides potential candidates for next generation of smart protein-mimetic materials.

Nanoporous PMMA foams with templated pore size obtained by localized in situ synthesis of nanoparticles and CO2 foaming

Polymer foams with controlled and templated pore size have been obtained for the first time by CO2 gas dissolution foaming from poly(methyl methacrylate) (PMMA) films. This kind of materials, with a variable porous structure, mimic some high-performance natural materials and could present significant interest in many applications. However, up to now their controlled fabrication has not been successfully achieved. Herein, we present a method to achieve a fine control in the production of such materials. Thermal in situ synthesis of ZnO nanoparticles from Zn(OAc)2 was proposed to obtain PMMA nanocomposites, in which the ZnO nanoparticles induce heterogeneous nucleation that leads to formation of pores with size below the micron, upon CO2 foaming. Starting from templated solid PMMA samples with well-differentiated regions, presenting or not ZnO nanoparticles, it was possible to obtain PMMA-based foams with well-defined areas of different pore sizes.

Engineered Control of Genetic Variability Reveals Interplay among Quorum Sensing, Feedback Regulation, and Biochemical Noise.

Stochastic fluctuations in gene expression trigger both beneficial and harmful consequences for cell behavior. Therefore, achieving a desired mean protein expression level while minimizing noise is of interest in many applications, including robust protein production systems in industrial biotechnology. Here, we consider a synthetic gene circuit combining intracellular negative feedback and cell-to-cell communication based on quorum sensing. Accounting for both intrinsic and extrinsic noise, stochastic simulations allow us to analyze the capability of the circuit to reduce noise strength as a function of its parameters. We obtain mean expression levels and noise strengths for all species under different scenarios, showing good agreement with system-wide available experimental data of protein abundance and noise in Escherichia coli. Our in silico experiments, validated by preliminary in vivo results, reveal significant noise attenuation in gene expression through the interplay between quorum sensing and negative feedback and highlight the differential role that they play in regard to intrinsic and extrinsic noise.

Lattice Boltzmann simulations of heat transfer in fully developed periodic incompressible flows.

Flow and heat transfer in periodic structures are of great interest for many applications. In this paper, we carefully examine the periodic features of fully developed periodic incompressible thermal flows, and incorporate them in the lattice Boltzmann method (LBM) for flow and heat transfer simulations. Two numerical approaches, the distribution modification (DM) approach and the source term (ST) approach, are proposed; and they can both be used for periodic thermal flows with constant wall temperature (CWT) and surface heat flux boundary conditions. However, the DM approach might be more efficient, especially for CWT systems since the ST approach requires calculations of the streamwise temperature gradient at all lattice nodes. Several example simulations are conducted, including flows through flat and wavy channels and flows through a square array with circular cylinders. Results are compared to analytical solutions, previous studies, and our own LBM calculations using different simulation techniques (i.e., the one-module simulation vs. the two-module simulation, and the DM approach vs. the ST approach) with good agreement. These simple, however, representative simulations demonstrate the accuracy and usefulness of our proposed LBM methods for future thermal periodic flow simulations.

Room‐Temperature Dielectric Switchable Nanocomposites

Room‐temperature switchable dielectric materials are of interest for many applications, including solar energy storage, smart switches, automatic filters, and next‐generation sensors. Here, a temperature‐triggered dielectric switchable nanocomposite by dispersing octadecylamine‐grafted multiwalled carbon nanotubes (ODA‐MWCNTs, for short) into hexadecane is reported. The composite has low permittivity at molten state and high permittivity at frozen state, and the permittivity switch is triggered around 18 °C. The highest permittivity contrast ratio reaches 106.4 at 2.0% CNT volume fraction. The composite shows frequency‐sensitive and temperature‐ramping‐rate‐sensitive properties. Further investigation indicates that the permittivity switch is caused by the change of the ODA‐MWCNT percolating networks during phase transition.

Simulation-based investigation of core-shell agglomerates: Influence of spatial heterogeneity in particle sizes on breakage characteristics

The stability and breakage behavior of agglomerates is of interest in many applications. It is well known that the internal microstructure is of great influence thereupon. However, the precise relationship of structural properties and mechanical behavior is not yet known for many scenarios. In this paper, we consider a flexible stochastic model to analyze the strength of spherical agglomerates consisting of spherical primary particles, arranged as core and shell. Structural properties can be varied in core and shell independently. Applying the bonded-particle model (BPM), we investigate the influence of the primary particle size distributions in core and shell on the breakage behavior under uniaxial compressive load. To get more meaningful results, we perform numerical studies of the same agglomerate with different directions of force and investigate the variation in breakage behavior.

Trapping time of excitons in Si nanocrystals embedded in a SiO2 matrix

Silicon (Si) nanocrystals (NCs) are of great interest for many applications, ranging from photovoltaics to optoelectonics. The photoluminescence quantum yield of Si NCs dispersed in SiO2 is limited, suggesting the existence of very efficient processes of nonradiative recombination, among which the formation of a self-trapped exciton state on the surface of the NC. In order to improve the external quantum efficiency of these systems, the carrier relaxation and recombination need to be understood more thoroughly. For that purpose, we perform transient-induced absorption spectroscopy on Si NCs embedded in a SiO2 matrix over a broad probe range for NCs of average sizes from 2.5 to 5.5 nm. The self-trapping of free excitons on surface-related states is experimentally and theoretically discussed and found to be dependent on the NC size. These results offer more insight into the self-trapped exciton state and are important to increase the optical performance of Si NCs.

Energy-conserving methods for the nonlinear Schrödinger equation

In this paper, we further develop recent results in the numerical solution of Hamiltonian partial differential equations (PDEs) (Brugnano et al., 2015), by means of energy-conserving methods in the class of Line Integral Methods, in particular, the Runge–Kutta methods named Hamiltonian Boundary Value Methods (HBVMs). We shall use HBVMs for solving the nonlinear Schrödinger equation (NLSE), of interest in many applications. We show that the use of energy-conserving methods, able to conserve a discrete counterpart of the Hamiltonian functional, confers more robustness on the numerical solution of such a problem.

Biomimetic polypeptides with reversible pH-dependent thermal responsive property

Smart protein-mimetic materials have received increasing interest for many applications. Here, we reported a facile and efficient approach to prepare a class of dual-responsive copoly(l-glutamate)s by ring-opening polymerization (ROP) and post-modification strategy. Both the oligo(ethylene glycol) (OEG) and glutamic acid residues were incorporated to offer thermal- and pH-responsive property simultaneously. We present a systematic study of the influence of both temperature and pH on the solution properties of the copolypeptides. The copolypeptides show entirely reversible pH-dependent thermal-responsive behaviors with tunable phase transition temperatures. It is demonstrated that the sequence of the polymer units can also influence the solution behavior. The α-helix conformation appears to be the dominant secondary conformation, which shows the pH dependence, but generally irrespective of the temperature. We further verify that the reduced circular dichroism (CD) signal upon heating above the clouding point (CP) is entirely due to the aggregation of the polymer chains. All these features make the obtained polypeptides potential candidates for next generation of smart protein-mimetic materials.