Two-phase Morphology Research Articles

The Role of Coherency Strains on Phase Stability in LixFePO4: Needle Crystallites Minimize Coherency Strain and Overpotential

We investigate the role of coherency strains on the thermodynamics of two-phase coexistence during Li (de)intercalation of . We explicitly account for the anisotropy of the elastic moduli and analytically derive coupled chemical and mechanical equilibrium criteria for two-phase morphologies observed experimentally. Coherent two-phase equilibrium leads to a variable voltage profile of individual crystallites within the two-phase region as the dimensions of the crystallite parallel to the interface depend on the phase fractions of the coexisting phases. With a model free energy for , we illustrate the effect of coherency strains on the compositions of the coexisting phases and on the voltage profile. We also show how coherency strains can stabilize intermediate solid solutions at low temperatures if phase separation is restricted to Li diffusion along the -axis of olivine . A finite element analysis shows that long needlelike crystallites with the long axis parallel to the lattice vector of minimize coherency strain energy. Hence, needlelike crystallites of reduce the overpotential needed for Li insertion and removal and minimize mechanical damage, such as dislocation nucleation and crack formation, resulting from large coherency strain energies.

Epitaxial self-assembly of multiferroic nanostructures

The morphology and structure of interfaces in PbTiO3–CoFe2O4 films on SrTiO3 substrates of various orientations are studied. It is found that for film with thickness more than 100 nm with columnar two-phase morphology, the average orientations of the interfaces between the phases reside on the {110}, {111}, and {112} planes for films normal to substrates oriented along ⟨001⟩, ⟨110⟩, and ⟨111⟩ correspondingly. These macroscopic interfaces consist of {111} nanofacets. The study of very thin film less than 30 nm shows that the interfaces between nanosize phases are {111} planes. Available theoretical results on morphology of multiferroic thin film nanostructure allow us to conclude that for thick films (>100 nm), two-phase columnar morphology (shape of constituent phases, their arrangement, and average crystallographic orientations of the interfaces) is essentially determined by the trend for minimization of elastic energy, while the trend to minimize the energy of interfaces results in faceting interfaces along the {111} planes. Possibility of long range ordering in phase arrangement is discussed.

Transmission electron microscopy study of phase morphology in polypropylene/ethylene-octene copolymer blends

Blends of polypropylene (PP) and ethylene-octene copolymers (EOC) were investigated by transmission electron microscopy (TEM) and by differential scanning calorimetry (DSC). The EOC contained 28, 37, 40 or 52 wt% of octene. Only the 50/50 PP/EOC ratio was used for all blends. None of the blends was fully miscible, there was always two-phase morphology. TEM observation followed by image analysis by ImageJ software revealed that the largest particles were in blend containing EOC-28 and the smallest were in blend with EOC-52. The coarsening rate at 200 °C was evaluated by TEM. The glass transition temperature ( T g) shift indicated partial miscibility. Partial miscibility was then confirmed by direct observation of bright PP lamellae in EOC dark phase.

A novel type of shape memory polymer blend and the shape memory mechanism

A novel styrene–butadiene–styrene tri-block copolymer (SBS) and poly(ɛ-caprolactone) (PCL) blend were introduced for its shape memory properties. Compared to the reported shape memory polymers (SMPs), this novel elastomer and switch polymer blend not only simplified the fabrication process but also offer a controllable approach for the study of mechanisms and the optimization of shape memory performances. Microstructures of this blend were characterized by differential scanning calorimetry (DSC), AFM microscope observation and tensile test. DSC results demonstrated the immiscibility between SBS and PCL. AFM images and stress–strain plot further confirmed the two-phase morphology within the blend. It was found that the SBS and PCL continuous phases contributed to the shape recovery and shape fixing performances, respectively. A detailed shape memory mechanism for this type of SMP system was then concluded and an optimized SMP system with both good recovery and fixing performances was designed from this mechanism.

Effect of polythiourethane hardener modification on the behaviour of epoxy resin

Polythiourethanes based on oligomeric polymercaptans were employed as curing agent of epoxy resin. The epoxy matrices, in the form of castings, were characterized for their mechanical properties such as tensile strength, elongation at break and unnotched Charpy impact strength as per ISO methods. Mechanical studies indicated that the incorporation of polythiourethane into epoxy resin improves the toughness and flexibility with reduction in tensile strength for samples cured at ambient conditions and influences the mechanical and thermal properties according to its percentage content for samples cured at 130°C. The high increase of impact strength was explained by the development of two-phase morphology during the cure process. The results of this study indicate that both the stoichiometry of the curing mixture and the initial thermal condition are of critical importance in governing the curing mechanism, structure of the network, morphology and the final properties of epoxy/polythiourethane compositions.

Microscopic morphology of blends between a new “all-acrylate” radial block copolymer and a rosin ester resin for pressure sensitive adhesives

With the goal of developing new pressure sensitive adhesive systems, the miscibility and the phase morphology of blends between novel symmetric four-arm star “all-acrylate” block copolymers synthesized by atom transfer radical polymerization (ATRP) and a rosin ester resin tackifier was studied with a combined differential scanning calorimetry (DSC) and atomic force microscopy (AFM) approach. Copolymer–resin compositions with increasing resin content in the blend were studied. The DSC results show good miscibility for compositions lower than 60 wt%, with a single glass transition at a temperature between those of the two pure compounds. The AFM results indicate that the initial two-phase morphology typical of the block copolymer matrix is preserved up to 60 wt% of resin. Above that value, a third phase, attributed to aggregates of the pure resin, is observed. Upon ageing, the homogeneous systems (e.g., blends with 40 wt% of resin) undergo a slow migration of the tackifying resin towards the surface of the sample, which can be understood in terms of surface free energy considerations. This eventually leads to the formation of a layer of pure resin at the surface.

Morphology of poly[(t-butyl acrylate)-b-styrene-b-isobutylene-b-styrene-b-(t-butyl acrylate)] pentablock terpolymers and their thermal conversion to the acrylic acid form

The morphology of a synthesized poly[(tert-butyl acrylate)-b-styrene-b-isobutylene-b-styrene-(tert-butyl acrylate)] pentablock terpolymer was determined using transmission electron microscopy, atomic force microscopy and small angle X-ray scattering methods. The outer blocks of this material were converted to the acrylic acid form by a thermal process that caused a beta-scission reaction in a simple thermal process, as verified by FTIR and NMR spectroscopies as well as thermogravimetric analysis. An initial heat-vacuum treatment induced a morphology that was more disordered relative to the precursor material, but when these samples were recast in THF solvent and annealed again, a considerably more refined and ordered morphology consisting of hexagonally packed cylinders resulted. This simple heat treatment allows for the tert-butyl groups to be converted to acrylic acid groups without dissolving the polymer or further sample cleaning. A dynamic mechanical investigation of the PtBuA form revealed three or two relaxation features depending interpretations based on the presence of three-phase morphology or a two-phase morphology in which there are mixed hard block domains.

Do thermal fluctuations influence the recoil loops of nanocomposite magnets?

An exchange-coupled FePt∕Fe3Pt nanocomposite system with well defined hard/soft two-phase morphology was prepared by reducing chemically synthesized FePt∕Fe3O4 bimagnetic nanoparticles. It was interesting to observe that the recoil loop openness is strongly dependent on the sweep rate of applied fields. A quantitative analysis shows a linear relation between the openness of recoil loops and the reciprocal activation volume, indicating that the recoil loops are intimately related to thermal fluctuation. The large open area of the recoil loops for nanocomposite magnets compared to that of single phase magnets is attributed to the unstable magnetic moments in the soft phase.

Phase Morphology and Mechanical Properties of Rubber-Toughened Polypropylene Nanocomposites: Effect of Elastomer Polarity

The objective of this work was to investigate the effect of elastomer polarity on phase structure and mechanical properties of PP nanocomposites. The nonpolar and polar elastomers studied were polyethylene octene (POE) and polyethylene octene grafted maleic anhydride (POEgMAH), respectively. The results from mechanical studies showed that the POEgMAH-toughened polypropylene nanocomposites have higher Izod impact strength but lower tensile and flexural properties than the unmaleated ones. X-ray diffraction (XRD) was used to characterize the formation of nanocomposites. XRD studies revealed that intercalated rubber-toughened PP nanocomposites (RTPPNC) had been successfully prepared where the macromolecule segments PP were intercalated into the interlayer space of organoclay. XRD also indicated that the incorporation of polar POEgMAH elastomers into PP nanocomposites contribute to a better intercalation effect and formed a more exfoliated combinations structure compared to POE. Scanning electron microscope (SEM) was used for the investigation of the phase morphology and rubber particle size and particle-size distribution. SEM study revealed a two-phase morphology where POE as droplets dispersed finely and uniformly in the PP matrix. The POEgMAH-toughened PP nanocomposites shows a much finer dispersion of elastomer particles than POE-toughened PP nanocomposites.

Combinatorial materials research applied to the development of new surface coatings IX: An investigation of novel antifouling/fouling-release coatings containing quaternary ammonium salt groups

Polysiloxane coatings containing chemically-bound (“tethered”) quaternary ammonium salt (QAS) moieties were investigated for potential application as environmental-friendly coatings to control marine biofouling. A combinatorial/high-throughput approach was applied to the investigation to enable multiple variables to be probed simultaneously and efficiently. The variables investigated for the moisture-curable coatings included QAS composition, ie alkyl chain length, and concentration as well as silanol-terminated polysiloxane molecular weight. A total of 75 compositionally unique coatings were prepared and characterized using surface characterization techniques and biological assays. Biological assays were based on two different marine microorganisms, a bacterium, Cellulophaga lytica and a diatom, Navicula incerta, as well as a macrofouling alga, Ulva. The results of the study showed that all three variables influenced coating surface properties as well as antifouling (AF) and fouling-release (FR) characteristics. The incorporation of QAS moieties into a polysiloxane matrix generally resulted in an increase in coating surface hydrophobicity. Characterization of coating surface morphology revealed a heterogeneous, two-phase morphology for many of the coatings investigated. A correlation was found between water contact angle and coating surface roughness, with the contact angle increasing with increasing surface roughness. Coatings based on the QAS moiety containing the longest alkyl chain (18 carbons) displayed the highest micro-roughness and, thus, the most hydrophobic surfaces. With regard to AF and FR properties, coatings based on the 18 carbon QAS moieties were very effective at inhibiting C. lytica biofilm formation and enabling easy removal of Ulva sporelings (young plants) while coatings based on the 14 carbon QAS moities were very effective at inhibiting biofilm growth of N. incerta.

Thermal properties and phase morphology of melt‐mixed poly(trimethylene terephthalate)/poly(hexamethylene isophthalamide) blends

AbstractThis work examines the thermal properties and phase morphology of melt‐mixed poly(trimethylene terephthalate) (PTT)/poly(hexamethylene isophthalamide) (PA 6I) blends. Two temperatures, i.e., 250 and 260°C, are used to prepare the blends, respectively. Differential scanning calorimetry results indicate the immiscible feature of the blends. It is thus concluded that the ester‐amide interchange reaction hardly occurred in the PTT/PA 6I blends. Depending on the composition and mixing temperature, the crystallization ability of PTT in the blends is either enhanced or hindered. Basically, a lower PA 6I content shifts the PTT melt crystallization to a higher temperature, whereas a higher PA 6I content causes an opposing outcome. The original complex melting behavior of neat PTT becomes more regular after the incorporation of 60 wt % or 80 wt % of PA 6I. Thermogravimetry analyses (TGA) show that the thermal stability of the blends improves as the PA 6I content increases. The two‐phased morphology of the blends is examined by scanning electron microscopy (SEM). Polarized light microscopy (PLM) results reveal that the PTT spherulites become coarser with the inclusion of PA 6I; only smaller/dispersed crystallites are observed in the blend with 20 wt % of PTT. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effect of carboxyl‐terminated butadiene acrylonitrile copolymer concentration on mechanical and morphological features of binary blends of nonglycidyl‐type epoxy resins

AbstractBlend samples were prepared by physical blending of nonglycidyl‐type epoxy resin with varying weight ratios of carboxyl‐terminated butadiene acrylonitrile (CTBN) copolymer ranging between 0 and 25 wt%. The blend samples were cured with stoichiometric quantity of diamine. A comparative study of prepared blend samples by Fourier transform infrared (FTIR) spectroscopy showed the modification as a result of chemical reactions between cycloaliphatic epoxy, CTBN, and 4,4′‐diamino diphenyl sulfone. The impact strength of the blend systems increased up to 15 wt% addition of CTBN in the blend and decreased thereafter. The toughness and elongation at break increased, whereas tensile strength decreased up to 20 wt% loading of CTBN in the blends. Two‐phase morphology appeared with the incorporation of CTBN in the cycloaliphatic epoxy resin matrix. © 2008 Wiley Periodicals, Inc. Adv Polym Techn 26:258–271, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20106

Synergic Effect of Acrylate Liquid Rubber and Bisphenol A on Toughness of Epoxy Resins

The synergic effect of acrylate liquid rubber with pendant epoxy group and bisphenol A on the toughness of epoxy resins was presented in this paper. The addition of bisphenol A enhances the impact strength and elongation at break of epoxy resin and actually increases the ductibility of epoxy resin matrix. Much higher toughness efficiency can be achieved for the ALR modified epoxy resins by the incorporation of bisphenol A at the same time. The synergic promotion effect of acrylate liquid rubber and bisphenol A on the toughness efficiency of epoxy resins is attributed to the two-phase morphology and high ductibility of matrix, and the resultant large stress white zones and high shear yielding during the fracture process.

Transmission electron microscopy of nanocomposite Cr [sbnd]B–N thin films

This paper reports on the preparation and characterization of Cr B N nanocomposite coatings for low friction, low wear and high thermostability applications. Sputtered Cr B N thin films were prepared in order to obtain a composite structure consisting of hard CrB 2 and CrN crystallites as well as hexagonal BN lubricant phase by unbalanced magnetron sputtering (UBM) of a CrB 2 target in an Ar/N 2 gas discharge. Coatings, with a total thickness of 4.5–5.5 μm, were deposited at 450 °C on silicon single-crystal substrates. A nanocomposite structure was obtained by increasing the nitrogen content of the sputtering gas. The coating microstructure was investigated on selected samples by high-resolution transmission electron microscopy. The films were generally found to consist of crystallites of a 1–4 nm size embedded in amorphous matrix. This crystalline phase was identified by electron diffraction as hexagonal CrB 2 for low nitrogen content and cubic CrN for high nitrogen content. In the medium composition range, the structure was amorphous, still keeping the two-phase morphology. The use of high-resolution imaging mode helped to reveal the composition of the amorphous phase which seems predominantly to consist of boron nitride.

Hydrodynamic cavitation and boiling in refrigerant (R-123) flow inside microchannels

This research article investigates the effect that hydrodynamic cavitation has on heat transfer. The fluid medium is refrigerant R-123 flowing through 227 μm hydraulic diameter microchannels. The cavitation is instigated by the inlet orifice. Adiabatic tests were conducted to study the two-phase cavitating flow morphologies and hydrodynamic characteristics of the flow. Diabatic experiments were performed resulting in surface temperatures under heat fluxes up to 213 W/cm 2 and mass velocities from 622 kg/m 2 s to 1368 kg/m 2 s. Results were compared to non-cavitating flows at the same mass velocities. It was found that the cavitating flows can significantly enhance the heat transfer. The heat transfer coefficient of the cavitating flows was larger than the non-cavitating flows by as much as 84%. Single-phase and two-phase heat transfer coefficients have been elucidated and employed to deduce the heat transfer mechanism prevailing under boiling conditions with and without the presence of cavitation.

Study on the morphology, rheology and surface of dynamically vulcanized chlorinated butyl rubber/polyethylacrylate extrudates: effect of extrusion temperature and times

A high-damping thermoplastic vulcanizate (TPV) composed of chlorinated butyl rubber (CIIR) and polyethylacrylate (PEA) was prepared by using a twin-screw extruder. The effect of extrusion temperature and times on the morphology, rheology and surface of the extrudates was examined and attempts were made to correlate the extrudate surface with the evolution of two-phase morphology and the rheological behavior. CIIR gel content of each extrudate was also analyzed. The result shows that CIIR gel content increases with increasing extrusion temperature or times; furthermore, extrusion at high temperature can produce numerous PEA and CIIR macromolecular radicals, thus chemical links take place between PEA and CIIR molecules. Morphological analysis indicates that phase inversion occurs at a gel content of around 68%, and with increasing extrusion times at high temperature the dispersed particles become larger and the particle edges become blurrier. All CIIR/PEA extrudates show pseudoplastic flow behavior. The extrusion temperature or extrusion times have a significant effect on melt viscosity of the extrudates. Surface analysis exhibits that co-continuous nature of the two-phase morphology results in melt fracture and periodic distortions on the extrudate surface, but with the increasing extrusion temperature or times the surfaces of the extrudates become gradually smooth.

Thermal properties and phase morphology of melt-mixed poly(trimethylene terephthalate)/polycarbonate blends—Mixing time effect

This work examined the mixing time effect on the thermal properties and phase morphology of melt-mixed blends of poly(trimethylene terephthalate) (PTT) with polycarbonate (PC). Differential scanning calorimetry (DSC) results indicated that the short time-mixed blends are miscible to a limited extent, with the PTT/PC-75/25 blend exhibiting the most miscibility. With increasing mixing time, the miscibility of the blends was enhanced, owing mostly to the occurrence of a transesterification reaction. The crystallization ability of PTT was hindered in the blends, and was further depressed with the increase in the mixing time. The PTT/PC-50/50 blend was inferred to possess the highest extent of transesterification after extended mixing. As revealed from thermogravimetry (TGA) analyses, the thermal stability of the blends declined as the mixing time increased; the blend with a higher PC content showed a higher degradation temperature. The original two-phased morphology was observed by scanning electron microscopy (SEM) to evolve to one homogeneous phase with increasing the mixing time for PTT/PC-75/25 and PTT/PC-50/50 blends. The PTT/PC-25/75 blend showed a higher resistance to developing the homogeneous phase morphology with mixing time, indicating less vulnerability to the transesterification reaction. The polarized light microscopy (PLM) results showed that the PTT spherulites became smaller or disappeared in the blends with increase in the mixing time.

Effect of carboxyl-terminated poly(butadiene- co-acrylonitrile) (CTBN) concentration on thermal and mechanical properties of binary blends of diglycidyl ether of bisphenol-A (DGEBA) epoxy resin

Six blend samples were prepared by physical mixing of epoxy resin with varying concentrations of liquid carboxyl-terminated butadiene acrylonitrile (CTBN) copolymer having 27% acrylonitrile content. The blend samples were cured with aromatic amine. A comparative study of Fourier-transform infrared (FTIR) spectra showed the modification as a result of chemical reactions between epoxide group, curing agent and CTBN. The tensile strength of cured blend samples decreased slightly from 11 to 46% where as the elongation-at-break showed an increasing trend with increasing rubber content, i.e., up to 25 phr, in the blend samples. Appreciable improvements in impact strength were also observed in the prepared blend systems. The glass transition temperature ( T g) of the epoxy resin matrix was slightly reduced on the addition of CTBN. The cured resin showed a two-phase morphology where the spherical rubber domains were dispersed in the epoxy matrix.

Morphological and Physical Properties of Triblock Copolymers of Methyl Methacrylate and 2-Ethylhexyl Methacrylate

Triblock copolymers of methyl methacrylate (MMA) and 2-ethylhexyl methacrylate (EHMA) [that is, poly(MMA-EHMA-MMA)] were prepared by an emulsion atom-transfer radical polymerization. The relationships of their structural, morphological, and physical properties were investigated. The latex particles had core-shell morphologies and the block copolymers experienced phase separation. Small latex particles with a low number of cores could deform and wet silicon-wafer surfaces, but the deformation of large latex particles was restricted by the internal two-phase morphology of the particles. Latex casting produced continuous pinholefree films, in which hard poly(MMA) (PMMA) cores of different latex particles merged and provided interparticle connections. The morphology of solution-cast films depended on block composition, solvent type, and film thickness. For all the prepared polymer samples, thick films cast in toluene had poly(EHMA) (PEHMA) materials at air surface, whereas those cast in tetrahydrofuran had a sponge-like PMMA surface structure. Thin toluene-cast films from P(MMA-EHMA-MMA) with the block degrees of polymerization (DP) 200-930-200 showed spherical PMMA domains and those from 380-930-380 yielded a protruded worm-like PMMA structure. The copolymer materials were coated on a glass surface for peeling tests. The films gave good hot-melt adhesion properties when the DP of the PEHMA block was over 600. The peeling strength depended on the lengths of both PEHMA and PMMA blocks. The P(MMA-EHMA-MMA) sample with DPs of 310-930-310 yielded the highest peeling strength of 7.4 kgf·inch -1 . The developed material is demonstrated to be a good candidate for a solvent-free, hotmelt, pressure-sensitive adhesives for special-purpose applications such as medical tapes and labels.

Morphology and mechanical properties of polyamide 12/polypropylene blends in presence and absence of reactive compatibiliser

Blends of polyamide 12 (PA12) and isotactic polypropylene (PP) were prepared by melt mixing in an internal mixer in presence and absence of compatibilisers. The compatibiliser used was maleic anhydride functionalised polypropylene (PP- g-MA). Effect of compatibilisation on the blends has been evaluated from the morphological parameters derived from scanning electron micrographs (SEM) of cryogenically fractured and extracted surfaces of the specimens. The uncompatibilised blends showed two-phase unstable morphology due to high interfacial tension and coalescence effects in the absence of favourable interactions at interface between the individual phases. Incompatibility increased as the concentration of dispersed phase in the blend increased. Compatibilisation stabilised the morphology by reducing the particle size as well as interparticle distance and enhancing the interfacial area and interface adhesion. A critical concentration of compatibiliser required for effective compatibilisation (CMC) was observed beyond which there was no net improvement in interfacial properties and was considered as the point of interfacial saturation. Experimental results were compared with the compatibilisation theories of Noolandi and Hong and Leibler and based on the calculated average interfacial area occupied per compatibiliser molecule it was concluded that the molecular state of compatibiliser at interface changed with concentration. It was supported by the rate constant for change in interfacial tension ( K) values which experienced a maximum at CMC followed by drastic reduction. Mechanical properties of the uncompatibilised blends showed inferior properties. It was found that compatibilisation significantly improved the mechanical properties. A good correlation has been observed between the mechanical properties and morphological parameters.