Development Of Phase Separation Research Articles

Complementary assessment of γ-irradiated polyurethane-POSS hybrids by chemiluminescence and differential scanning calorimetry

A series of segmental polyurethane organic inorganic hybrids with polyhedral oligomeric silsesquioxanes (POSS) incorporated along the chain contour on the hard segments is irradiated by γ radiation at doses up to 100 kGy. The effects of this treatment on the morphology of the materials and the low temperature stability to oxidation are assessed complementary by non-isothermal and isothermal chemiluminescence experiments as well as with differential scanning calorimetry. From the methodological point of view, it was found that both physical and chemical processes have a footprint on both methods, but the physical ones manifest themselves more intensely in the thermal method, whereas chemical ones in chemiluminescence. Due to γ-exposure the onset oxidation temperatures decrease by several degrees, but POSS seems to protect the material to some extent. γ-Irradiation damage has also a negative effect on the development of phase separation, which is further enhanced by the presence of POSS. The crystallinity of the soft segments in the matrix is completely suppressed by irradiation, however, even a small amount of POSS preserves the phenomenon.

Unveiling the science behind the tea bowls from the Jizhou kiln. Part I. Chemical compositions and the two-layer glazing technique

The Jizhou kiln, a folk kiln of ancient China, is well-known for the production of black-glazed tea bowls. Polished cross sections showed a white opaque glazed surface covering a black lower layer and a light brown opaque layer existed between them. Analysis by X-ray fluorescence yielded two different calcia-alkali glaze compositions-a black ground glaze and a white cover glaze. Using multi-variable factor-loading analysis, the two-layer glazes were compared to those on white, greenish-white and white-rim black porcelains, in order to understand the variability. In addition, compositions of bodies were compared to the glaze compositions to determine if the same porcelain stone was used along with ash to form the glaze. Based on the physicochemical foundation of the glazes, the opacification of the white cover glazes was due to the phase separation between SiO2 and CaO. It is the combined contribution of melting, bubbling, flowing and diffusion between the cover and ground glazes, as well as the development of phase separation during the firing process, that bring about the “Yao Bian” tea bowls.

Crystallization‐Induced Phase Separation in Solution‐Processed Small Molecule Bulk Heterojunction Organic Solar Cells

The driving forces and processes associated with the development of phase separation upon thermal annealing are investigated in solution‐processed small molecule bulk heterojunction (BHJ) organic solar cells utilizing a diketopyrrolopyrrole‐based donor molecule and a fullerene acceptor (PCBM). In‐situ thermal annealing X‐ray scattering is used to monitor the development of thin film crystallization and phase separation and reveals that the development of blend phase separation strongly correlates with the nucleation of donor crystallites. Additionally, these morphological changes lead to dramatic increases in blend electron mobility and solar cell figures of merit. These results indicate that donor crystallization is the driving force for blend phase separation. It is hypothesized that donor crystallization from an as‐cast homogeneous donor:acceptor blend simultaneously produces donor‐rich domains, consisting largely of donor crystallites, and acceptor‐rich domains, formed from previously mixed regions of the film that have been enriched with acceptor during donor crystallization. Control of donor crystallization in solution‐processed small molecule BHJ solar cells employing PCBM is thus emphasized as an important strategy for the engineering of the nanoscale phase separated, bicontinuous morphology necessary for the fabrication of efficient BHJ photovoltaic devices.

Features of the spatial distribution of indium in InGaN epitaxial layers grown by plasma-assisted molecular beam epitaxy

The processes leading to the formation of a spatially nonuniform distribution of indium in the InxGa1 − x N layers with x = 0−0.6 grown by molecular beam epitaxy with plasma activation of nitrogen at relatively low growth temperatures (590–630°C) are studied. It is found that at low values of x < 0.1, the growth proceeds pseudomorphically at least to a thickness of 70 nm, and these layers are characterized by a high uniformity of the In distribution, which confirms their thermodynamic stability. Upon increasing x up to ∼0.3, the signs of a nonuniform In distribution are observed, which is associated with the stress relaxation facilitating the development of phase separation. It is shown that layers with In distribution of lower uniformity feature more intense photoluminescence in the energy range 2.0–2.5 eV. For the layers with x = 0.6, complete phase separation is observed with the formation of several phases with a wide range of compositions, including the region in the vicinity of the InN binary compound.

Effect of Nanofillers on Phase Separation Behaviour of Diblock Copolymer: A Molecular Dynamic Study

Polymer nanocomposites are recognized as the next generation of polymer composites due to their exceptional properties. Understanding the molecular origin of the reinforcement mechanism is crucial to the development of such promising materials. This paper reports our recent molecular dynamic study on clay-based polyurethane nanocomposites. The effect of clay platelets on phase separation behavior of polyurethane, at the clay-polyurethane interface, is quantified in terms of molecular interactions, structure and dynamics. The results show that the nanoconfinement of polyurethane chains in clay gallery impedes the development of phase separation commonly observed in bulk polyurethane. The absence of phase separation of intercalated polyurethane is believed to be related to the competitive interactions among clay platelet, polyurethane and surfactant.

Phase separation and dynamic patterning inCu1−xCoxfilms under ion irradiation

Phase separation behavior in thin ${\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}$ films under irradiation ($1.8\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ ${\mathrm{Kr}}^{+}$ ions) at different temperatures has been systematically studied for $0.10\ensuremath{\leqslant}x\ensuremath{\leqslant}0.20$. The development of phase separation in irradiated films (estimates of the average size of Co precipitates and concentration of Co in solution) was monitored using magnetic measurements. Analysis of magnetization data in the framework of superparamagnetic theory has shown that at irradiation temperatures $T\ensuremath{\leqslant}330\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, phase separation in $\mathrm{Cu}--\mathrm{Co}$ films of all compositions stabilizes at high doses $(\ensuremath{\approx}1\ifmmode\times\else\texttimes\fi{}{10}^{16}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2})$, indicating the existence of temperature-dependent dynamic steady states. At temperatures higher than $\ensuremath{\approx}350\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, indications of thermodynamic-like coarsening are observed. Below $\ensuremath{\approx}300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ FC/ZFC (field-cooled/zero-field cooled) measurements clearly show the randomizing effect of irradiation. The observed phase separation behavior of $\mathrm{Cu}--\mathrm{Co}$ system under irradiation agrees qualitatively well with kinetic Monte Carlo simulations performed in this work and with theoretical predictions of phase evolution in irradiated immiscible alloys.

Amorphous nanostructuring in potassium niobium silicate glasses by SANS and SHG: a new mechanism for second-order optical non-linearity of glasses

Potassium niobium silicate (KNS) glasses xK 2O xNb 2O 5(1−2 x)SiO 2 with x=0.167; 0.182; 0.200; 0.220 and 0.250 have been subjected to prolonged heat treatments in a wide temperature range above T g. As a result, glasses exhibiting liquid-type phase separation phenomena have been isolated. Moreover for each glass composition, the temperature zones have been determined to produce transparent, opalescent or opaque materials which have been studied by X-ray diffraction (XRD), small-angle neutron scattering (SANS) and second harmonic generation (SHG) techniques. SANS data unambiguously point at nanostructuring of KNS glasses in the scale of 5–20 nm under appropriate heat treatments near T g. In contrast to initial KNS glasses, nanostructured glasses exhibit SHG activity. For earliest stages of phase separation SHG-active glasses are characterized by fully amorphous XRD patterns. Further development of phase separation in glasses with increasing of their opalescence leads to diminishing SHG, and subsequently partial crystallization takes place giving opaque materials. Since relative maximum of SHG efficiency corresponds to non-crystalline nanostructured glasses, such new transparent second-order non-linear media may be of both scientific and practical interest. With regard to non-crystalline structure of nano-inhomogeneities, SHG mechanism in the glasses is supposed to be due to a combination of third-order non-linearity with a spatial modulation of linear polarizability.

Concurrent ordering and phase separation in the vicinity of the metastable critical point of order–disorder transition in Fe–Si alloys

Transmission electron microscopy was employed in study of microstructural change due to phase separation from B2 to ( B2+ D0 3) in Fe-base binary alloys with 12.4 and 13.8 at.% Si, which were annealed at temperatures around the critical line of metastable order–disorder transition between B2 and D0 3 expected within the miscibility gap. Dark-field images have shown that fine fluctuations of the degree of order appear in the early stage and then gradually fade away with development of phase separation in the following stage. These fluctuations are regarded as due to the thermal dissipation effect pronounced around the critical temperature of metastable order–disorder transition. It suggests that the critical point retains attributes of the second-order transition even inside the two-phase field, and it plays a role as the limit of metastability and instability for quenched B2 phase against phase separation into ( B2+ D0 3). Besides, a roughening transition of 〈100〉/2 antiphase boundaries has been recognized in D0 3 phase in Fe–14.6 at.%Si at a temperature 1024 K slightly lower than the critical point of equilibrium B2– D0 3 order–disorder transition around 1030 K. The antiphase boundaries wander through the D0 3 matrix in the narrow temperature range between the two transitions, contrary to faceted orientation to {100} at lower temperature.

ELECTRIC-FIELD-INDUCED PHASE SEPARATION IN ELECTRORHEOLOGICAL FLUIDS

The phase separation into a high-density and a low-density phase, which occurs after a strong electric field is applied to an ER fluids, is demonstrated in terms of the Coulomb interaction energy of the system. The phase separation is manifested by two-dimensional pattern observed in the field direction by means of a pair of transparent glass (TG) electrodes. The development of phase separation with an increasing field is recorded by a computer image processing system consisting of a CCD video camera. The patterns are irregular and their characteristic sizes are determined by two-dimensional auto-correlation approach. The dependency of those patterns on external electric field is analyzed based on statistical methods. Two critical fields are presented to characterize the electric-field-induced phase separation process in the ER fluid.

Formation of Percolated Structure During Solvent Casting of Polymer Blend-solvent Systems.

The development of phase separation in ternary systems composed of polybutadiene-poly(styrene-co-butadiene)-good solvent was studied by time-resolved light-scattering during the solvent casting process. Double percolated structures with two different periodic distances were observed for the thick film. The structure with the smaller periodic distance was formed at the surface of films and the larger one was formed inside the film. It was found that the periodic distance for the larger percolated structure was proportional to (tP – tS)0.6, where (tP – tS) is the lapse of the time from the start of phase separation to fixation of the structure. The time dependence of the wave number, qm, at which the light-scattering intensity reaches maximum, was correlated by a similar relationship. The intensity of light scattering at qm was proportional to qm3.3 irrespective of the solvent-casting conditions. The development of the percolated structure was qualitatively interpreted by numerical analysis of an equation describing spinodal decomposition and an equation expressing the time dependence of the polymer concentration in the cast solution.

Adiabatic reactive viscometry for polyurethane reaction injection molding

AbstractAdiabatic reactive rheometry involves the simultaneous measurement of viscosity and temperature changes during adiabatic polymerization. Using the adiabatic reactor method to relate temperature to fractional conversion results in a useful rheokinetic tool ideally suited for fastreacting reaction injection molding (RIM) systems for which the mold‐filling step is nearly adiabatic. In this work, a small laboratory RIM machine is used to mix the reactants and deliver them to a constant stress rheometer retrofitted with a wide‐gap Couette geometry and two thermocouples. Measurements on two polyurethane systems are reported. A simple cross‐linking system is used to verify the adiabatic rheokinetic method through comparison to a known gel conversion. Subsequent measurements on a phase‐separating RIM system show that increases in catalyst level, hard segment content, and initial reactant temperature result in a decreased gel time and an increased gel conversion. The viscosity rise profiles aid our understanding of the onset and development of phase separation. They are also essential for mold‐filling models and establishing moldability criteria for these RIM systems.