An investigation on the pressure-induced phase transition of nanocrystalline ZnS

An in situ energy dispersive x-ray diffraction study on nanocrystalline ZnS was carried out under high pressure up to 30.8 GPa by using a diamond anvil cell. The phase transition from the wurtzite to the zinc-blende structure occurred at 11.5 GPa, and another obvious transition to a new phase with rock-salt structure also appeared at 16.0 GPa-which was higher than the value for the bulk material. The bulk modulus and the pressure derivative of nanocrystalline ZnS were derived by fitting the Birch-Murnaghan equation. The resulting modulus was higher than that of the corresponding bulk material, indicating that the nanomaterial has higher hardness than the bulk material.

Pressure-induced phase transition of nanocrystalline zinc sulfide

In situ energy dispersive X-ray diffraction measurements on nanocrystalline zinc sulfide have been performed by using diamond anvil cell with synchrotron radiation. There is a phase transition which the ultimate structure is rocksalt when the pressure is up to 16.0GPa. Comparing the structure of body materials, the pressure of the phase transition of nano zinc sulfide is high. We fit the: Birch-Murnaghan equation of state and obtained its ambient pressure bulk modulus and its pressure derivative. The bulk modulus of nanocrystalline zinc sulfide is higher than that of body materials, it indicate that the rigidity of nanocrystalline zinc sulfide is high.

Electric field-induced conformational transition of bovine serum albumin from alpha-helix to beta-sheet

The irreversible conformational transition of bovine serum albumin (BSA) from alpha-helix to beta-sheet, induced by electric field near the electrode surface, was monitored by circular dichroism (CD) with a long optical path thin layer cell (LOPTLC).

Intrinsic spin hall effect induced by quantum phase transition in HgCdTe quantum wells

The spin Hall effect can be induced by both extrinsic impurity scattering and intrinsic spin-orbit coupling in the electronic structure. The HgTe/CdTe quantum well has a quantum phase transition where the electronic structure changes from normal to inverted. We show that the intrinsic spin Hall effect of the conduction band vanishes on the normal side, while it is finite on the inverted side. By tuning the Cd content, the well width, or the bias electric field across the quantum well, the intrinsic spin Hall effect can be switched on or off and tuned into resonance under experimentally accessible conditions.

Electric field driven quantum phase transition between band insulator and topological insulator

We demonstrate theoretically that electric field can drive a quantum phase transition between band insulator to topological insulator in CdTe/HgCdTe/CdTe quantum wells. The numerical results suggest that the electric field could be used as a switch to turn on or off the topological insulator phase, and temperature can affect significantly the phase diagram for different gate voltage and compositions. Our theoretical results provide us an efficient way to manipulate the quantum phase of HgTe quantum wells.

Observation of inverted phases in poly(styrene-b-butadiene-b-styrene) triblock copolymer by solvent-induced order-disorder phase transition

We report observation of inverted phases consisting of spheres and/or cylinders of the majority fraction block in a poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer by solvent-induced order-disorder phase transition (ODT). The SBS sample has a molecular weight of 140K Da and a polystyrene (PS) weight fraction of 30%. Tapping mode atomic force microscopy (AFM) and transmission electron microscopy (TEM) were utilized to study the copolymer microstructure of a set of solution-cast SBS films dried with different solvent evaporation rates, R. The control with different R leads to kinetic frozen-in of microstructures corresponding to a different combination parameter chi (eff)Z of the drying films (where chi (eff) is the effective interaction parameter of the polymer solution in the cast film and Z the number of "blobs" of size equal to the correlation length one block copolymer chain contains), for which faster evaporation rates result in microstructures of smaller chi (eff)Z. As R was decreased from rapid evaporations (similar to0.1 mL/h), the microstructure evolved from a totally disordered one sequentially to inverted phases consisting of spheres and then cylinders of polybutadiene (PB) in a PS matrix and finally reached the equilibrium phase, namely cylinders of PS in a PB matrix. We interpret the formation of inverted phases as due to the increased relative importance of entropy as chi (eff)Z is decreased, which may dominate the energy penalty for having a bigger interfacial area between the immiscible blocks in the inverted phases.

Structural studies of excimer laser-induced percolative phase transition on polyimide thin film surfaces

The behavior of electrical conductivity for excimer laser irradiated polyimide films in the vicinity of the critical number of laser shots was described by three-dimensional percolative phase transition model. It is: found that electrical conductivity changed more rapidly than that predicted by the percolation model. Thus, the change in microstructure with increasing number of laser shots was analyzed by FT-IR Raman spectrometry and laser desorption time-of-flight mass spectrometry. It is demonstrated that not only the number but also the average size of graphite particles on the irradiated polyimide film surfaces increased with increasing number of laser shots. These results were helpful to better understand the critical change in electrical conductivity on the irradiated polyimide film surfaces. (C) 2001 Elsevier Science B.V. All rights reserved.

Rotation-driven prolate-to-oblate shape phase transition in W-190: A projected shell model study

A shape phase transition is demonstrated to occur in W-190 by applying the projected shell model, which goes beyond the usual mean-field approximation. Rotation alignment of neutrons in the high-j, i(13/2) orbital drives the yrast sequence of the system, changing suddenly from prolate to oblate shape at angular momentum 10h. We propose observables to test the picture.

Antikaon condensation and deconfinement phase transition in neutron stars

Antikaon condensation and deconfinement phase transition in neutron stars are investigated in a chiral hadronic model (also referred as to the FST model) for the hadronic phase and in the MIT bag model for the deconfined quark matter phase. It is shown that the existence of quark matter phase makes antikaon condensation impossible in neutron stars. The properties of neutron stars are sensitive to the bag constant. For the small values of the bag constant, the pure quark matter core appears and hyperons are strongly suppressed in neutron stars, whereas for the large bag constant, the hadron-quark mixed phase exists in the center of neutron stars. The maximum masses of neutron stars with the quark matter phase are lower than those without the quark matter phase; meanwhile, the maximum masses of neutron stars with the quark matter phase increase with the bag constant.

Phase transition behavior and molecular orientation of oligo(9,9 '-dioctylfluorene-alt-bithiophene)

A novel conjugated oligomer, oligo(9,9'-dioctylfluorene-alt-bithiophene) (OF8T2), was found to exhibit a unique phase transition between crystalline and liquid-crystalline states, and a liquid-crystalline glass was easily generated, offering better TFT device performance. In thin films, upon annealing the OF8T2 molecules oriented preferentially with their planes of conjugation being normal to the substrate, and both film thickness and annealing temperature were critical to the film morphology and the molecular orientation. When the OF8T2 film was deposited on a rubbed polyimide surface and annealed, the molecules aligned their long axes along the rubbing direction.

Morphology and crystalline transition of poly (3-butylthiophene) associated with its polymorphic modifications

Poly (3-butylthiophene) (P3BT) is a much less studied conjugated polymer despite its high crystallizability and thus excellent electrical property. In this work, morphology of P3BT at different crystalline polymorphs and solvent/thermal induced phase transition between form I and U modifications have been intensively investigated by using optical microscopy, electron microscopy, differential scanning calorimetry, and X-ray diffraction. It is shown that a direct deposition from carbon disulfide (CS2) at fast evaporation results in P3BT crystals in form I modification, giving typical whiskerlike morphology. In contrast, low evaporation rate from CS, leads to formation of form II crystals with spherulitic morphology, which is so far scarcely observed in polythiophene.

Electric-field-induced molecular alignment of side-chain liquid-crystalline polyacetylenes containing biphenyl mesogens

Electric-field-induced molecular alignments of side-chain liquid-crystalline polyacetylenes [-{HC=C[(CH2)(m)OCO-biph-OC7H15]}-, where biph is 4,4'-biphenylyl and m is 3 (PA3EO7) or 9 (PA9EO7)] were studied with X-ray diffraction and polarized optical microscopy. An orientation as high as 0.84 was obtained for PA9EO7. Furthermore, the molecular orientation of]PA9EO7 was achieved within a temperature range between the isotropic-to-smectic A transition temperature and 115 degreesC, and this suggested that the orientational packing was affected by the thermal fluctuation of the isotropic liquid and the mobility of the mesogenic moieties. The maximum achievable orientation for PA9EO7 was much greater than that for PA3EO7. This was the first time that the electric-field-induced molecular orientation of a side-chain liquid-crystalline polymer with a stiff backbone was studied.

Inverted to normal phase transition in solution-cast polystyrene-poly(methyl methacrylate) block copolymer thin films

We have investigated the inverted phase formation and the transition from inverted to normal phase for a cylinder-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer in solution-cast films with thickness about 300 nm during the process of the solution concentrating by slow solvent evaporation. The cast solvent is 1, 1,2,2-tetrachloroethane (Tetra-CE), a good solvent for both blocks but having preferential affinity for the minority PMMA block. During such solution concentrating process, the phase behavior was examined by freeze-drying the samples at different evaporation time, corresponding to at different block copolymer concentrations, phi. As phi increases from similar to 0.1 % (nu/nu), the phase structure evolved from the disordered sphere phase (DS), consisting of random arranged spheres with the majority PS block as I core and the minority PMMA block as a corona, to ordered inverted phases including inverted spheres (IS), inverted cylinders (IC), and inverted hexagonally perforated lamellae (IHPL) with the minority PMMA block comprising the continuum phase, and then to the lamellar (LAM) phase with alternate layers of the two blocks, and finally to the normal cylinder (NC) phase with the majority PS block comprising the continuum phase. The solvent nature and the copolymer solution concentration are shown to be mainly responsible for the inverted phase formation and the phase transition process.

Electrostatic-field-induced chain alignment of liquid crystalline copolyether TPP thin films

A liquid crystalline (LC) copolyether has been synthesized from 1-(4-hydroxy-4'-biphenyl)-2-(4-hydroxyphenyl)propane with 1,7-dibromoheptane and 1,11-dibromoundecane with a 50/50 (both in %) equal composition of the 7- and 11-methylene monomers [coTPP-7/11(5/5)]. A mono-domain with a homeotropic alignment can be induced by a thin film surface in the LC phase. When an electrostatic field is applied to the surface-induced mono-domains parallel to the thin film surface normal, the molecular alignment undergoes a change from the homeotropic to uniaxial homogeneous arrangement. However, when the field is applied to a direction perpendicular to the thin film surface normal. the molecular alignment is about 10 degrees -tilt with respect to the homeotropic alignment toward the a*-axis. This is because the permanent dipole moment of the copolyether is not right vertical to the molecular direction. The calculation of molecular dipoles indicates that the permanent dipole moment of this copolyether is about 70 degrees away from the molecular axis, which leads to a negative dielectric anisotropy. It is speculated that the 10 degrees- rather than 20 degrees -tilt is due to a balance between the alignment induced by the electrostatic field and the surface. In the electrostatic field, molecules are subjected to a torque tau, which is determined by the permanent dipole moment P and the electrostatic field E: tau = P x E. The molecular realignment in both parallel and perpendicular directions to the thin film surface normal is determined by satisfying the condition of tau = P x E = 0. (C) 2001 Elsevier Science Ltd. All rights reserved.