Biphasic Particles Research Articles

Properties of laser cladding (NiCoCr)94Al3Ti3-cBN-hBN hard self-lubricating ceramic coating

Titanium alloy is an essential material for preparing aerospace engines because of its excellent performance. However, the poor wear resistance of titanium alloy restricts its further development as a critical engine material. This study aimed to use laser cladding and particle enhancement technologies to enhance the surface wear resistance of titanium alloy. (NiCoCr)94Al3Ti3+hBN, (NiCoCr)94Al3Ti3+cBN, and (NiCoCr)94Al3Ti3+hBN + cBN were prepared on the surface of titanium alloy, and the wear resistance mechanism of single-phase self-lubricating particles, single-phase hard particles, and self-lubricating and hard biphasic particles was investigated. The results showed that the microhardness of the biphase-reinforced coating was 1083.8 HV0.5, which was higher than that of the self-lubricating particle-reinforced coating and hard-particle-reinforced coating by 368.4 HV0.5 and 149.8 HV0.5, respectively. The friction coefficient of the biphase-reinforced coating was 0.4208, which was lower than that of the self-lubricating particle-reinforced coating and hard-particle-reinforced coating by 0.0224 and 0.0686, respectively. The wear rate of the biphase-reinforced coating was 0.076 mm3/NM, and the wear resistance of the biphase-reinforced coating was 3.42 and 1.37 times that of the self-lubricating particle-reinforced coating and hard-particle-reinforced coating, respectively. hBN relied on its own decomposition to promote the coating to present a layered unstable structure to achieve a wear reduction effect, cBN relied on its own hardness to resist wear and played a wear-resistant role, whereas biphase-reinforced coating had a hard wear resistance and formed a lubricating film to enhance the wear resistance of the coating. The comprehensive performance of the dual-phase wear-resistant coating reinforced by hard particles and self-lubricating particles was better than that of single-phase wear-resistant coating, providing a reference for developing wear-resistant coating integrating hardness and self-lubrication.

Formation of Pt-Pd 'Janus' Biphasic Particles During High-Temperature Aging of Diesel Oxidation Catalysts.

Formation of Pt-Pd 'Janus' Biphasic Particles During High-Temperature Aging of Diesel Oxidation Catalysts.

One-Step Synthesis of Biphasic, Cavity-forming Polymer Particles via Dispersion Copolymerization of Styrene and Sulfobetaine Methacrylate.

A one-step dispersion copolymerization technique is demonstrated to fabricate biphasic particles as an approach to streamline the production of particles with complex morphology. The model system studies a monomer feed of hydrophobic styrene and hydrophilic, zwitterionic sulfobetaine methacrylate (SBMA) in a water/isopropanol cosolvent mixture. The resulting particles have a core-shell morphology that can be transformed, simply by washing the particles with water, into particles with a single surface opening connected to an interior cavity. Results indicate that particle morphology is dependent on the presence of nanoscopic SBMA-rich aggregates in the initial reaction mixture to act as nucleation sites, forming an SBMA-rich core encased in a styrene-rich shell. Systematic study of the morphology evolution reveals that the difference in monomer solubility profile can be exploited to control compositional drift of the particle composition during copolymerization yielding copolymer with sufficiently different composition to form phase-separated particle morphology. When SBMA is replaced with various ionic comonomers, the cavity-forming morphology is observed when reaction conditions result in low solubility of the comonomer in the cosolvent mixture. Based on these results, design guidelines are developed that may be applied to a variety of systems requiring complex and responsive particles made from chemically distinct comonomer pairings.

Electrostatic Stabilization of Nano Liquid Metals in Doped Nonpolar Liquids

AbstractLiquid metals and alloys are attracting renewed attention owing to their potential for application in various advanced technologies. Eutectic gallium‐indium (EGaIn) has been focused on in particular because of its integrated advantages of high conductivity, low melting point, and low toxicity. In this study, the colloidal behavior of nano‐dispersed EGaIn in nonpolar oils is investigated. Although the nonpolar oil continuous phase is commonly considered to be free of electric charges, electrostatic repulsion appears to be crucial in the colloidal stabilization of the nano‐dispersed EGaIn phases, the modulation of which is possible by doping the oil phases with different types of oil‐soluble surfactants. The qualitative correlation between the observed colloidal stabilities and the “zero field” particle mobilities inferred from the field‐dependent electrophoretic mobilities indicates that the electric charging of EGaIn particles in surfactant‐doped nonpolar oils is a static phenomenon that is maintained in equilibrium, rather than a solely field‐induced process. A systematic investigation of the charging properties of these unique biphasic particles, consisting of the liquid Ga‐In bulk and the solid Ga2O3 surface that formed spontaneously, reveals the complicated system‐dependent nature of the charging mechanisms mediated by ionic and nonionic surfactants in nonpolar media.

A Co‐ and Ni‐Free P2/O3 Biphasic Lithium Stabilized Layered Oxide for Sodium‐Ion Batteries and its Cycling Behavior

AbstractCobalt‐ and nickel‐free cathode materials are desirable for developing low‐cost sodium‐ion batteries (SIBs). Compared to the single P‐type and O‐type structures, biphasic P/O structures become a topic of interest thanks to improved performance. However, the added complexity complicates the understanding of the storage mechanism and the phase behavior is still unclear, especially over consecutive cycling. Here, the properties of biphasic P2(34%)/O3(60%) Na0.8Li0.2Fe0.2Mn0.6O2and its behavior at different states of charge/discharge are reported on. The material is composed of single phase O3 and P2/O3 biphasic particles. Sodium occupies the alkali layers, whereas lithium predominantly (95%) is located in the transition metal layer. An initial reversible capacity of 174 mAh g‐1is delivered with a retention of 82% dominated by Fe3+/Fe4+along with contributions from oxygen and partial Mn3+/4+redox. Cycling leads to complex phase transitions and ion migration. The biphasic nature is nevertheless preserved, with lithium acting as the structure stabilizer.

Aerosol Optical Tweezers Constrain the Morphology Evolution of Liquid-Liquid Phase-Separated Atmospheric Particles

Summary Chemical models of atmospheric particles are vital in understanding the role of aerosol particles in atmospheric chemistry, air pollution, human health, and climate change. Advancing these models requires new frameworks that can realistically predict how critical particle properties evolve. We present such a framework for predicting particle phase separation and which morphology will prevail; this controls how each particle interacts with and affects the atmosphere. We studied the mixing behavior of α-pinene secondary organic aerosol (SOA) with different organic phases, as relative humidity was varied to determine the interplay between polarity, miscibility, interfacial tension, and the resulting morphology. Using measurements from aerosol optical tweezers experiments and literature data, a general trend in morphology with increasing atmospheric oxidation was observed, from biphasic partially engulfed (where both phases are immediately accessible to the gas phase) to biphasic core shell (where the organic shell conceals the core) and finally to a single-phase, homogeneous morphology.

Evolutionary lattice model for the compaction of pervious concrete in the fresh state

This paper presents a simplified model for the simulation of the compaction of deformable granular materials such as pervious concrete in the fresh state. The strategy is to use an evolutionary lattice system with local instability to simulate the intensive internal rearrangement expected during compaction. This is associated with a bar layout and material properties that vary with the time steps. Furthermore, a biphasic particle composed by a rigid inner core involved by a deformable exterior layer is considered. This versatile approach allows a simplified representation of complex granular media made of very deformable particles or of rigid particles covered by a flexible binder. Numerical and experimental comparisons were conducted to evaluate the capacity of the method to predict the behavior of different materials. The results indicate that the model may provide an estimation of the forces applied during the compaction, being suitable for a wide range of applications.

Hybrid biphasic microparticles based on polyhedral oligomeric silsesquioxanes

Biphasic eggshell-like microparticles based on poly(ε-caprolactone) (PCL)/octaisobutyl polyhedral oligomeric silsesquioxanes (octa-iBuPOSS) hybrid blends were prepared by controlling the phase separation process during single spinneret electrospraying. The biphasic eggshell-like microparticles contained a PCL-rich shell and a very hydrophobic octa-iBuPOSS-rich inner phase, which cannot be achieved otherwise. The study of octa-iBuPOSS-based model system demonstrates that the electrospraying can be employed to fabricate biphasic particles through manipulating the phase separation process. The facile fabrication of the eggshell-like particles reported here provided valuable insight into not only the controlled release of very hydrophobic drugs but also the surface coating of medical devices where hydrophobic molecules are necessary but required to be encapsulated inside biocompatible materials.

Effect of particle size distribution on particle based composite anode models

Particle based models of composite anodes are useful tools for exploring the behavior of SOFC systems. As part of our efforts to develop models for understanding fuel cells, we have been building models of Ni-YSZ composite anodes using experimentally measured particle size distributions. The objectives of this study were to characterize the percolation threshold and conductivity of these models in comparison to simpler mono dispersed and biphasic particle size distributions from the literature. We found that the average values for the onset of percolation and the measured conductivity of the models with experimentally measured particle size distributions are similar to those for the simple distributions and the experimentally measured distributions. For all of the configurations evaluated, the onset of percolation in the Nickel phase occurred at a solid fraction of Nickel between 20% and 25%. This corresponded almost exactly to the point at which the coordination number between Nickel phase particles reached 2.2. The significant finding was that the variation in the value for the conductivity, as measured by the standard deviation of the results, was several orders of magnitude higher than for the simpler systems. We explored the validity of our assumptions, specifically the assumption of random particle placement, by building a particle model directly from FIB-SEM data. In this reconstruction, it was clear that the location of particles was not random. Particles of the same type and size had much likelihood of contact higher than would indicated by random location.

Self-Assembly of Janus Cylinders into Hierarchical Superstructures

We present in-depth studies of the size tunability and the self-assembly behavior of Janus cylinders possessing a phase segregation into two hemicylinders. The cylinders are prepared by cross-linking the lamella-cylinder morphology of a polystyrene-block-polybutadiene-block-poly(methyl methacrylate) block terpolymer. The length of the Janus cylinders can be adjusted by both the amplitude and the duration of a sonication treatment from the micro- to the nanometer length. The corona segregation into a biphasic particle is evidenced by selective staining of the PS domains with RuO(4) and subsequent imaging. The self-assembly behavior of these facial amphiphiles on different length scales is investigated combining dynamic light scattering (DLS), small-angle neutron scattering (SANS), and imaging procedures. Cryogenic transmission electron microscopy images of the Janus cylinders in THF, which is a good solvent for both blocks, exhibit unimolecularly dissolved Janus cylinders with a core-corona structure. These results are corroborated by SANS measurements. Supramolecular aggregation takes place in acetone, which is a nonsolvent for polystyrene, leading to the observation of fiber-like aggregates. The length of these fibers depends on the concentration of the solution. A critical aggregation concentration is found, under which unimolecularly dissolved Janus cylinders exist. The fibers are composed of 2-4 Janus cylinders, shielding the inner insoluble polystyrene hemicylinder against the solvent. Herein, the SANS data reveal a core-shell structure of the aggregates. Upon deposition of the Janus cylinders from more concentrated solution, a second type of superstructure is formed on a significantly larger length scale. The Janus cylinders form fibrillar networks, in which the pore size depends on the concentration and deposition time of the sample.

Spatioselective Modification of Bicompartmental Polymer Particles and Fibers via Huisgen 1,3‐Dipolar Cycloaddition

AbstractPrecise nano‐ and microscale control of the architecture of biodegradable biomaterials is desirable for several biotechnological applications such as drug delivery, diagnostics, and medical imaging. Herein, we combine electrohydrodynamic co‐jetting and highly specific surface modification (via Huisgen 1,3‐dipolar cycloaddition) to prepare particles and fibers with spatioselective surface modification. We first prepared biphasic particles and fibers from commercial poly(lactide‐co‐glycolide) copolymers via electrohydrodynamic co‐jetting of two organic solutions loaded with fluorescent macromolecules and acetylene‐modified PLGA derivatives. (i) Spatially controlled reaction of poly[lactide‐co‐(propargyl glycolide)] with O‐(2‐aminoethyl)‐O′‐(2‐azidoethyl)heptaethylene glycol and (ii) subsequent conversion of the newly introduced amino groups with fluorescence probes resulted in particles and fibers with surface modification of one hemisphere only.magnified image

Engineering Nanostructured Polymer Blends with Controlled Nanoparticle Location using Janus Particles

Janus particles are used on a multigram scale for the blend compatibilization of two polymers in a twin screw mini-mixer. It is shown that the Janus particles can be located exclusively at the interface of the two polymer phases despite the high temperature and shear conditions. The domain sizes of the dispersed phase decrease with increasing content of Janus particles. The decrease is yet ongoing for high contents of Janus particles. Furthermore, the biphasic particles exhibit an ordered arrangement at the interface. Thus, the approach demonstrates that a nanoscopic structuring of the interface can be achieved under macroscopic processing conditions. The structural order occurs on two levels. The first is the complete adsorption at the interface and the second is the lateral ordering at the interface. The strong adsorption at the interface is explained in terms of the increased desorption energy of Janus particles. Secondly, the compatibilization efficiency is critically compared to state-of-the-art compatibilizers. The efficiency of the Janus particles is found to be superior as compared to block copolymer-based compatibilizers. The efficiency gap between Janus particles and block copolymer compatibilizers widens for larger amounts added.

Bicompartmentalized Polymer Particles by Tandem ROMP and ATRP in Miniemulsion

This study describes an original approach to prepare biphasic particles by simultaneous ring-opening metathesis polymerization (ROMP) of norbornene and atom-transfer radical polymerization (ATRP) of methyl methacrylate under miniemulsion conditions. A single water-soluble ruthenium macrocatalyst was used to initiate ROMP and mediate ATRP. All situations led to high conversions, and well-distributed particles containing two incompatible homopolymers grown under controlled conditions could indeed be prepared.

New insights into the nucleation and growth of PS nodules on nanoparticles by 3D cryo-electron tomography.

The nucleation and growth of polystyrene (PS) nodules on 170 nm silica seeds under emulsion-polymerization conditions have been investigated for the first time by cryo-electron tomography. 3D arrangements were reconstructed from samples collected at several polymerization times (from 5 to 120 min). Early samples display the presence of small PS nodules bound to silica particles in a random distribution. For longer polymerization times, the number of PS nodules per silica seed decreases leading to octopod-like morphologies. The tomographic method allowed us to measure the contact angle that the growing PS nodules form with the silica bead surface. The average value of 142.4° remains constant over all of the observed period of the polymerization reaction. This contact angle appeared to be one of the key parameters for controlling the morphology of PS-silica biphasic particles.

Poly(ethylene‐co‐vinyl acetate)‐graft‐poly(methyl methacrylate) (EVA‐graft‐PMMA) as a modifier of epoxy resins

AbstractConventional approaches to toughen thermosets are: (1) the polymerization‐induced phase separation of a rubber or a thermoplastic, or (2) the use of a dispersion of preformed particles in the initial formulation. In the present study it is shown that it is possible to combine both techniques by using graft copolymers with one of the blocks being initially immiscible and the other that phase separates during polymerization. This is illustrated by the use of poly(ethylene‐co‐vinyl acetate)‐graft‐poly(methyl methacrylate) (EVA‐graft‐PMMA) as modifier of an epoxy resin. EVA is initially immiscible and PMMA phase separates during polymerization. Blends of an epoxy monomer based on diglycidylether of bisphenol A (DGEBA, 100 parts by weight), piperidine (5 parts by weight), and PMMA (5 parts by weight), showed the typical polymerization‐induced phase separation of PMMA‐rich domains before gelation of the epoxy network. Replacing PMMA by EVA‐graft‐PMMA (5 parts by weight), yielded stable dispersions of EVA blocks, favoured by the initial solubility of PMMA blocks. Phase separation of PMMA blocks in the course of polymerization led to a dispersion of in situ generated biphasic particles (plausibly composed of EVA cores surrounded by PMMA shells), with average diameters varying from 0.3 to 0.6 µm with the cure temperature. This procedure may be used to generate stable dispersions of biphasic particles for toughening purposes.© 2002 Society of Chemical Industry

Influence of the Addition of Polystyrene-block-poly(methyl methacrylate) Copolymer (PS-b-PMMA) on the Morphologies Generated by Reaction-Induced Phase Separation in PS/PMMA/Epoxy Blends

Homogeneous solutions of polystyrene (PS) and poly(methyl methacrylate) (PMMA) in diglycidylether of bisphenol A, containing about 8 wt.-% total thermoplastic, and with or without 0.5 wt.-% of a PS-b-PMMA block copolymer, were polymerized in two ways (i) in the presence of a tertiary amine (benzyldimethylamine, BDMA), or (ii) using a stoichiometric amount of a diamine (4,4′-diaminodiphenyl sulfone, DDS). A double phase-separation was recorded by light transmission during polymerization. A PS-rich phase was separated at low conversions and a PMMA-rich phase was segregated at more advanced conversions. The addition of the block copolymer produced significant changes in the morphologies generated. For the BDMA-initiated polymerization, the presence of the block copolymer made the small PMMA-rich domains clearly discernible in transmission electron microscopy (TEM) micrographs. For the DDS-cured system, the addition of the block copolymer led to a dispersion of small PS-rich particles encapsulated by PMMA shells. The possibility of generating a stable dispersion of biphasic particles by polymerization-induced phase separation opens a new way to modify thermosetting polymers for toughening purposes.

Preparation of novel titania photocatalysts with high activity

New anatase photocatalysts have been prepared by a hydrothermal technique. The powders have been shown to have a high photocatalytic activity, which is believed to be derived from their high crystallinity and phase purity resulting in fewer defects that can allow pre-emptive recombination of the free electron and positive hole. Bi-phasic particles containing both the anatase and brookite phases have also been prepared, but these have much lower photocatalytic activity.