Metastability and phase coexistence are important concepts in colloidal science. Typically, the phase diagram of colloidal systems is considered at the equilibrium without the presence of an external field. However, several studies have reported phase transition under mechanical deformation. The reason behind phase coexistence under shear flow is not fully understood. Here, multilamellar vesicle (MLV)‐to‐sponge (L3) and MLV‐to‐Lα transitions upon increasing temperature are detected using flow small‐angle neutron scattering techniques. Coexistence of Lα and MLV phases at 40 °C under shear flow is detected by using flow NMR spectroscopy. The unusual rheological behavior observed by studying the lamellar phase of a non‐ionic surfactant is explained using 2H NMR and diffusion flow NMR spectroscopy with the coexistence of planar lamellar–multilamellar vesicles. Moreover, a dynamic phase diagram over a wide range of temperatures is proposed. 相似文献
Block copolymer nanopaticles were prepared from the mixture solutions containing good/poor solvents by a simple evaporation process. The block copolymers formed disorder, unidirectionally stacked lamellar, and onion‐like structures in nanoparticles depending on preparation temperatures. Thermal annealing induced the disorder‐order phase transition and order‐order phase transformation in the block copolymer nanoparticles, even though the annealing temperature is lower than the of one polymer segment. The unusual thermal behaviors suggest that the glass transition temperature of the block copolymer is decreased by the effect of nanoparticle, whose surface areas are larger than their volumes.
1 INTRODUCTION In recent years, much attention has been focused on the NaxCoO2 system due to its notable properties and potential technologic applications as a cathode material in high-energy density, reversible solid state battery systems[1, 2]. Recently, large thermoelectric power[3～6] in NaxCoO2 and superconductivity (～4 K) in hydrated NaxCoO2yH2O (x = 0.35, y = 1.33) ma- terial have been observed[7]. This hydrated layered phase is the first 3d-transition metal oxide with superco… 相似文献
The nanocrystalline cubic, tetragonal, and submicron monoclinic phases of pure zirconia were prepared by thermal decomposition of carbonate and hydroxide precursors. The crystallization and isothermal phase transformations of the oxide were studied using high temperature X‐ray diffraction, X‐ray diffraction and Raman spectra of quenched samples. Cubic zirconia formed first, and then progressively transformed to tetragonal and monoclinic phases at temperatures as low as 320°C. The cubic, tetragonal, and monoclinic phases for ZrO2 were found to be distinct functions of crystallite size, indicating the nanocrystalline nature of these phases. They were found to exist within critical size ranges of 50 to 140 Å, 100 to 220 Å and 190 to 420 Å (±5 Å), respectively. Thus, as the crystallites grow during annealing, they first transform from cubic to tetragonal and then from tetragonal to monoclinic at critical sizes. The classical Avrami equation for nucleation and growth was applied to the tetragonal to monoclinic phase transition. 相似文献
The present report deals with some results on phase behavior, miscibility and phase separation for several polymer blends casting from solutions. These blends are grouped as the amorphous polymer blends, blends containing a crystalline polymer or two crystalline polymers. The blends of PMMA/PVAc were miscible and underwent phase separation at elevated temperature, exhibited LCST behavior. The benzoylated PPO has both UCST and LCST nature. For the systems composed of crystalline polymer poly(ethylene oxide) and amorphous polyurethane, of two crystalline polymers poly(-caprolactone) and poly[3,3,-bis-(chloromethyl) oxetane], appear a single Tg, indicating these blends are miscible. The interaction parameter B's were determined to be –14 J cm–3, –15 J cm–3 respectively. Phase separation of phenolphthalein poly(ether ether sulfone)/PEO blends were discussed in terms of thermal properties, such as their melting and crystallization behavior.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
Boron is an important element, used in applications from superhard materials to superconductors. Boron exists in several forms (allotropes) and, surprisingly, it was not known which form (α or β) is stable at ambient conditions. Through experiment, we quantify the relative stability of α‐boron and β‐boron as a function of temperature. The ground‐state energies of α‐boron and β‐boron are nearly identical. For all temperatures up to 2000 K, the complicated β‐boron structure is more stable than the simpler α‐boron structure at ambient pressure. Below 1000 K, β‐boron is entropically stabilized with respect to α‐boron owing to its partially occupied sites, whereas at higher temperatures β‐boron is enthalpically stabilized with respect to α‐boron. We show that α‐boron only becomes stable on application of pressure. 相似文献
