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1.
The phase behavior of ABC triblock and AB diblock copolymer melts is investigated by self-consistent field theory, while allowing for (among other candidates) the orthorhombic Fddd (O70) network phase identified in recent experiments with poly(isoprene-b-styrene-b-ethylene oxide) (ISO) triblocks. Predicted phase diagrams for triblocks similar to ISO contain an O70 phase bordered by gyroid, lamellar, and alternating gyroid phases, in agreement with experiment. The O70 network is also found to be stable in diblock melts within a narrow region that overlaps the weak segregation end of the gyroid region found in previous calculations. 相似文献
2.
3.
G.H. Fredrickson F.S. Bates 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(1):71-76
We suggest that ABC triblock copolymers provide a convenient and effective route to emulsifying blends of A and C homopolymers
into co-continuous morphologies over a wide range of compositions. Direct transitions between disordered tricontinuous phases
(“ABC microemulsions”) and spatially-periodic tricontinuous phases (e.g. gyroid or double-diamond cubic phases) should be possible in appropriately formulated alloys. We envision a broad range of
potential applications to thermoplastic and thermoset polymeric materials.
Received: 4 June 1997 / Revised: 17 September 1997 / Accepted: 13 October 1997 相似文献
4.
Dotera T 《Physical review letters》2002,89(20):205502
Using the Monte Carlo lattice-simulation technique, we present numerical evidence of the formation of gyroid and nongyroid tricontinuous cubic phases in high polymeric systems of ABC/A/C triblock copolymer and homopolymer blends. By increasing the volume fraction of homopolymer, a remarkable phase sequence G (gyroid) --> D (diamond) --> P (primitive) is observed, which is common to certain surfactant systems. Our results indicate that the ABC triblock copolymer system with blending homopolymers may be a zoo of cubic phases, suitable for comparative studies of these phases. 相似文献
5.
The shear-induced ordering of lamellar and gyroid structures of a nonionic surfactant C16E7/D2O system in a Couette shear cell ( 0.001 < < 10 s-1, : shear rate) has been investigated by using a small angle neutron scattering technique. In the lamellar phase, the steady
shear flow having > 0.01 s-1 suppresses undulation fluctuations of lamellae (Maxwell effect). This suppression of fluctuations brings two effects; 1)
shear-induced lamellae ordering toward a parallel orientation and 2) obstruction of a lamellar↦gyroid transition. It is quite
interesting to note that there is a characteristic shear rate range ( 0.01 < < 0.3 s-1), where both effects take place. We have also investigated the shear effects on the gyroid phase. Below the characteristic
shear rate range, the gyroid structure keeps three-dimensional network lattice, while above the characteristic shear rate
range, the gyroid structure transforms to the parallel orientation lamellae (shear-induced gyroid-lamellar transition). Thus
the shear flow having the characteristic shear rate plays very important roles in shear ordering phenomena.
Received 26 June 2000 and Received in final form 12 January 2001 相似文献
6.
Sary N Brochon C Hadziioannou G Mezzenga R 《The European physical journal. E, Soft matter》2007,24(4):379-384
We report on the self-assembly behaviour of two homologue series of rod-coil block copolymers in which, the rod, a π -conjugated
polymer, is maintained fixed in size and chemical structure, while the coil is allowed to vary both in molecular weight and
chemical nature. This allows maintaining constant the liquid crystalline interactions, expressed by Maier-Saupe interactions,
ω , while varying the tendency towards microphase separation, expressed by the product between the Flory-Huggins parameter
and the total polymerization degree, χN . Therefore, the systems presented here allow testing directly some of the theoretical predictions for the self-assembly
of rod-coil block copolymers in a weakly segregated regime. The two rod-coil block copolymer systems investigated were poly(DEH-p-phenylenevinylene-b-styrene),
whose self-assembly takes place in the very weakly segregated regime, and poly(DEH-p-phenylenevinylene-b-4vinylpyridine),
for which the self-assembly behaviour occurs under increased tendency towards microphase separation, hereby referred to as
moderately segregated regime. Experimental results for both systems are compared with predictions based on Landau expansion
theories. 相似文献
7.
Jinnai H Nishikawa Y Spontak RJ Smith SD Agard DA Hashimoto T 《Physical review letters》2000,84(3):518-521
Self-consistent field theory predicts that the complex phase behavior of block copolymers does not originate solely from the interface seeking constant mean curvature as once thought, but instead reflects competing minimization of interfacial tension and packing frustration. To test this prediction, we directly measure interfacial curvature distributions from a 3D image reconstruction of the bicontinuous gyroid morphology. Results obtained here reveal that the gyroid interface is not constant mean curvature and confirm the importance of packing frustration in the stabilization of such complex nanostructures. 相似文献
8.
V.A. Pryamitsyn A.N. Semenov T.C.B. McLeish 《The European physical journal. E, Soft matter》2001,4(2):161-171
An analytical one-dimensional model of the microphase separation in symmetric diblock copolymers is developed. Three stages
of the process of the microphase segregation of a quenched diblock copolymer system into a lamella structure are predicted.
The first stage involves a fast increase of the amplitude of the quasi-periodical lamella structure (with the average wave
vector q0) up to a nearly equilibrium value; the second stage is a slow phase diffusion process which is characterized by increasing
coherency of the lamella structure; the third stage is the slow process of the lamella swelling, which is driven by the thermally
activated process of the spontaneous deletion of excessive lamellas, the lamella size increasing from the initial value 2π/q
0 to the equilibrium 2π/q
eq > 2π/q
0 during the process. The last two stages are described with the specially introduced coarse-grained “amplitude-phase” approximation.
It is shown that the relaxation of the gradient of the phase of the lamellar structure is the slowest relaxation process and,
thus, can be used as an effective order parameter of the lamellar structure at the later stages of the microphase segregation.
Received 10 March 2000 and Received in final form 5 June 2000 相似文献
9.
利用扩展x射线吸收精细结构和x射线衍射研究了机械合金化制备的体心立方(bcc)的亚稳态Fe80Cu20合金固溶体的结构随退火温度的变化特点.结果表明,在300—873 K温度范围内,随着退火温度的升高,bcc结构物相的晶格常数近于线性降低,这主要是由于Cu原子从bcc结构Fe80Cu20合金固溶体中逐渐偏析出来,生成面心立方(fcc)结构的Cu物相所致.经603K退火后,Cu原子的平均键长RCu—Cu增加了0.003 nm左右,大约有50%的Cu原子从bcc结构的Fe80Cu20合金固溶体中偏析出来.在773 K退火后,bcc结构Fe80Cu20合金固溶体近于完全相分离,生成了bcc结构的α-Fe与fcc结构的Cu物相.
关键词:
扩展x射线吸收精细结构
x射线衍射
80Cu20合金')" href="#">Fe80Cu20合金
机械合金化 相似文献
10.
M. Hillberg W. Stieler F. J. Litterst V. Burkhardt O. Nuyken 《Hyperfine Interactions》1994,88(1):137-147
Mössbauer absorption spectra of glassy block and copolymers with lowT
G containing ferrocene have been recorded in a wide temperature range (4–330 K) to investigate the dynamical processes of the system, in the glassy state and around the glass transition. An inhomogeneous broadening due to conformational substates with different hyperfine parameters found at lower temperatures becomes motionally narrowed above 40 K. Whereas in the glassy state both the block and the copolymers reveal the same vibrational behaviour, we found differences in the vicinity of their respective glass transitions. For the block polymer an anomalous decrease of the recoilfree fractionf
A was found above the static glass transition. In agreement with neutron data on other polymers we attribute this behaviour to an onset of motions of the ferrocene units of higher than 1010 Hz. For the copolymers, however, a departure of lnf
A from linearity was detected already far below the staticT
G. We propose that this is caused by residual solvents which allow an easier cooperative rearrangement of the segments even belowT
G. First attempts to interpret the Mössbauer data by means of the predictions of the mode coupling theory are reported. 相似文献
11.
E. P. Elsukov A. V. Protasov I. V. Povstugar 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(3):339-342
The sequence of solid state reactions upon the mechanical alloying of Mo and Fe powders with an 80: 20 atomic ratio was established by means of Mössbauer spectroscopy and X-ray diffraction. At the first stage, a nanostructure and Mo63Fe37 hexagonal close packed (HCP) phase are formed in Mo body-centered cubic lattice (BCC) particles. At the second stage, a body-centered cubic lattice of Mo-Fe solid solution is formed. The process is accompanied by the formation of a minor amount (about 20%) of X-ray amorphous phase. 相似文献
12.
We show, by computer simulation, that tapered or pear-shaped particles, interacting through purely repulsive interactions, can freely self-assemble to form the three-dimensionally periodic, gyroid cubic phase. The Ia3d gyroid cubic phase is formed by these particles on both compression of an isotropic configuration and expansion of a smectic A bilayer arrangement. For the latter case, it is possible to identify the steps by which the topological transformation from nonintersecting planes to fully interpenetrating, periodic networks takes place. 相似文献
13.
P. Pieranski L. Sittler P. Sotta M. Imperor-Clerc 《The European physical journal. E, Soft matter》2001,5(3):317-328
Monocrystals of the cubic lyotropic liquid crystal phase V1 are studied in droplets of the mixture C
12
EO
6/water surrounded by water vapor of controlled pressure p. Shapes of monocrystals are found to depend on the conditions of growth from the lamellar phase and on the nature of the
substrate. After the growth, when the lamellar phase is exhausted and crystals are in equilibrium with water vapors, their
shapes are shown to depend on the pressure p. Thermodynamic aspects of these phenomena are discussed.
Received 22 November 2000 相似文献
14.
Shusharina NP Alexandridis P Linse P Balijepalli S Gruenbauer HJ 《The European physical journal. E, Soft matter》2003,10(1):45-54
A mean-field lattice theory is applied to predict the self-assembly into ordered structures of an ABC triblock copolymer in
selective solvent. More specifically, the composition-temperature phase diagram has been constructed for the system (C)14(PO)12(EO)17/water, where C stands for methylene, PO for propylene oxide and EO for ethylene oxide. The model predicts thermotropic phase
transitions between the ordered hexagonal, lamellar, reverse hexagonal, and reverse cubic phases, as well as the disordered
phase. The thermotropic behavior is a result of the temperature dependence of water interaction with EO- and PO-segments.
The lyotropic effect (caused by changing the solvent concentration) on the formation of different structures has been found
weak. The structure in the ordered phases is described by analyzing the species volume fraction profiles and the end segment
and junction distributions. A “triple-layer” structure has been found for each of the ordered phases, with each layer rich
in C-, PO-, and EO-segments, respectively. The blocks forming the layers are not stretched. The dependence of the domain spacing
on polymer volume fraction and temperature is also considered.
Received 17 April 2002 Published online: 21 January 2003 相似文献
15.
运用扩展的自洽场和密度泛函理论(SCF/DFT),研究ABC蝌蚪形两亲高分子在稀溶剂中的自组装形态,其中蝌蚪形两亲高分子由线形嵌段共聚物链AB嫁接到球形纳米颗粒C上构成.与以往研究的线形ABC两亲高分子相比,蝌蚪形两亲高分子的自组装形态有着很大的不同.在粒子亲溶剂,嵌段共聚物疏溶剂时,各组分间弱分凝条件下,蝌蚪形两亲高分子自组装成胶球状形貌;在强分凝条件下,随着嵌段共聚物疏溶剂性的增强,两亲高分子的自组织态由胶球状转变成四角、三角状形貌,其中嵌段B主要分布在各角上.通过改变各组分间的相互作用,在嵌段A亲溶剂,嵌段B和粒子疏溶剂时,粒子呈平行棒状或小方块状分布在胶球中. 相似文献
16.
An amorphous phase has been produced in a binary Nb-19 at .% Si alloy by rapidly quenching from the molten state. Primary decomposition of the amorphous phase by annealing resulted in the production of a small quantity of the A15 cubic Nb3Si phase. However, long annealing treatments led to the complete transformation to the equilibrium phases. Application of high pressure of 10 GPa during decomposition of the amorphous phase resulted firstly in the improved stability of the amorphous phase and secondly, in the production of a much larger quantity of the A15 cubic Nb3Si phase. The lattice parameter of this phase was calculated to be 0.515 nm, in conformity with the previous investigations. 相似文献
17.
A two or more chemically different homopolymers attached to a single junction point form a macromolecule of miktoarm star copolymer. The model of such copolymer composed of an arbitrary number of types of homopolymer arms is considered. The lengths distributions of arms are assumed to be arbitrary, provided that average length of an each arm is long enough. The algorithm is suggested to find the contributions into the Landau free energy of this copolymer melt which are necessary to obtain a phase diagram in weak segregation regime. Using this algorithm the contributions are found up to the fourth order. The phase diagrams have been constructed for the simple model of AB2 copolymer melt whose macromolecules consist of polydisperse A-block and two monodisperse B-blocks. 相似文献
18.
Incorporation of the protein cytochrome c (cyt c) into the hydrated bicontinuous Ia3d cubic mesophase of monoolein (MO) was investigated within a wide range of pressures by small-angle X-ray scattering (SAXS). We found that incorporation of cyt c into the cubic phase of MO has a drastic effect on the structure and pressure stability of the system: At high pressures, the lipid systems with less than 0.2 wt.% embedded protein undergo a transition to a fluid lamellar phase with smaller partial molar lipid volume. Incorporation of cyt c at levels above 0.2 wt.% promotes the formation of a new cubic phase, probably a cubic micellar phase of space group P4332 (Q212) whose pressure stability rises with increasing protein content. 相似文献
19.
R. R. Rodriguez J. L. Valenzuela J. A. Tabares G. A. Pérez Alcázar 《Hyperfine Interactions》2014,224(1-3):323-330
Fe65Ni35 samples were prepared by mechanical alloying (MA) with milling times of 5, 6, 7, 10 and 11 h, using a ball mass to powder mass ratio of 20:1 and at 280 rpm. The samples were characterized by X-ray diffraction (XRD) and transmission 57Fe Mössbauer spectrometry. The X-ray diffraction pattern showed the coexistence of one body centered cubic (BCC) and two face centered cubic (FCC1 and FCC2) structural phases. The lattice parameters of these phases did not change significantly with the milling time (2.866 Å, 3.597 Å and 3.538 Å, respectively). After 10 h of milling, the X-ray diffraction pattern showed clearly the coexistence of these three phases. Hence, Mössbauer spectrometry measurements at low temperatures from 20 to 300 K of this sample were also carried out. The Mössbauer spectra were fitted using a model with three components: the first one is a hyperfine magnetic field distributions at high fields, related to the BCC phase; the second one is a hyperfine magnetic field distribution involving low hyperfine fields related to a FCC phase rich in Ni, and the third one is a singlet related to a FCC phase rich in Fe, with paramagnetic behavior. As proposed by some authors, the last phase is related with the antitaenite phase. 相似文献
20.
Microstructure and properties of 6FeNiCoSiCrAlTi high-entropy alloy coating prepared by laser cladding 总被引:3,自引:0,他引:3
The content of each constituent element in the newly developed high-entropy alloys (HEAs) is always restricted in equimolar or near-equimolar ratio in order to avoid the formation of complex brittle phases during the solidification process. In this study, a 6FeNiCoSiCrAlTi high-entropy alloy coating with simple BCC solid solution phase has been prepared by laser cladding on a low carbon steel substrate. The microstructure, hardness and magnetic properties have been investigated. The experimental results show that the tendency of component segregation in the conventional solidification microstructure of multi-component alloy is effectively relieved. The microstructure of the coating is mainly composed of equiaxed polygonal grains, discontinuous interdendritic segregation and nano-precipitates. EBSD observation confirms that the polygonal grains and interdendritic segregation have similar BCC structure with lots of low angle grain boundaries at the interface. The microhardness of the coating reaches 780 HV0.5, which is much higher than most of the HEAs prepared by other methods. In addition, the coating shows excellent soft magnetic properties. 相似文献