Dynamics of transient metastable states in mixtures under coupled phase ordering and chemical demixing

We present theory and simulation of simultaneous chemical demixing and phase ordering in a polymer-liquid crystal mixture in conditions where isotropic-isotropic phase separation is metastable with respect to isotropic-nematic phase transition. In the case the mechanism is nucleation and growth, it is found that mesophase growth proceeds by a transient metastable phase that surround the ordered phase, and whose lifetime is a function of the ratio of diffusional to orientational mobilities. In the case of spinodal decomposition, different dynamic regimes are observed depending on the mobility ratio: metastable phase separation preceding phase ordering, phase ordering preceding phase separation, or simultaneous phase ordering and phase separation. Not only the overall dynamics but also the final structure of the material can be different for each kinetic regime.     

Long-lived population of the metastable 2s state in muonic hydrogen

Preliminary experimental results of the search for long-lived metastable μp(2s) are presented. The μp(2s) are identified via muon transfer to neon in a gas mixture of hydrogen and several percent of neon at mbar pressures. An energy-dependent 1s transfer rate to neon has been observed. The time spectra can only be explained assuming a nonzero μp(2s) population. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electronic structure and magnetism of metastable bcc Co(001)

The electronic structure and magnetism of thin films of metastable bcc phase Co(001) consisting of one-, five- and nine-layers is determined by means of all-electron local spin density full potential linearized augmented plane wave (FLAPW) calculations at the lattice constant found for bcc Co stabilized on a GaAs substrate by Prinz. Band structure, surface states, density of states, charge and spin densities and contact hyperfine fields are presented. The center layer of the many-layer films yields a spin magnetic moment of 1.76μ_B which agrees well with results of bulk calculations for bcc Co. The surface layer has a moment (1.94μ_B) which is only 10% greater than the bulk value - in sharp contrast to the enhancement found for other transition metal surfaces [35% for Fe(001), 20% for Ni(001) and over 300% for Cr(001)]. Unlike these other transition metal surfaces, even the first layer below the surface layer in Co has the bulk magnetic moment - which indicates that the spin density, like the charge density, shows very short range screening of the surface-vacuum interface.     

Shear thinning and orientational ordering of wormlike micelles

Shear thinning and orientation of cylindrical surfactant and block copolymer micelles was investigated by rheo-SANS (small-angle neutron scattering) experiments. Shear thinning and orientation occur for shear rates (.)gamma tau(dis)>1, where tau(dis) is the disentanglement time of the micelles. Micelles align in the flow direction with an orientational distribution that can be well described by an Onsager-type distribution function. Over nearly the whole range of concentrations and for all cylindrical micelles investigated, the shear viscosity eta follows a simple eta approximately e(-aS) behavior as a function of the orientational order parameter S with the same prefactor a.     

Global symmetry breaking in the nonconserved order parameter system during phase ordering

We study global symmetry breaking in the 2D system of scalar nonconserved order parameter following a quench to zero temperature. We show that the instant of time when the symmetry is broken and the final morphology is chosen corresponds to the saturation of the order parameter inside the domains. There are three possible final morphologies: the positive and negative order parameter final morphology, and the state of the coexisting positive and negative order parameter subsystems with a flat interface between them. We find also that each type of the final morphology constitutes about 1/3 of all cases, what agrees with the results obtained recently by Spirin et al. [Phys. Rev. E 65, 016119 (2001)]. Our results are pertinent for the two dimensional systems, but we suspect that there is also a way to apply similar arguments for the three dimensional ones.     

A high-modulus metastable phase in Mg-Ni-Y alloys

The evolution of the elastic properties and the character of the structural changes occurring during the crystallization of amorphous Mg-Ni-Y alloys are investigated. The process of crystallization is shown to proceed in two stages with formation of an intermediate metastable phase at the first stage. This phase has higher elastic characteristics than those of the stable crystalline phases of this system.     

A metastable phase forming during crystallization of an amorphous Ni70Mo10P20 alloy

The evolution of the structure of an amorphous Ni₇₀Mo₁₀P₂₀ alloy during annealing in the temperature range from 673 to 873 K is studied using x-ray diffraction and transmission electron microscopy. It is found that a previously unknown metastable phase forms during crystallization of the amorphous Ni₇₀Mo₁₀P₂₀ alloy. The morphology of the newly formed crystals is studied, the space group and the lattice constant are determined, and the atom positions for the phase that forms are proposed. It is found that the metastable phase is a phosphide whose composition is close to (Ni(Mo))₃P. We established that, as the temperature or the duration of annealing is increased further, the metastable phase turns into the equilibrium Ni₃P phase. The orientation relations between the metastable and equilibrium phases are determined.     

Nuclear spin magnetic ordering with four spin exchange in solid bcc 3He

Some consequences of four spin exchange are analysed: 1) the negative sign of the T^-3 term in the specific heat; 2) the existence of thirteen possible magnetic arrangements, in particular a pseudo-ferromagnetic pahse; 3) a susceptibility, in the ordered phase, larger than that deduced from the Heisbnberg Hamiltonian.     

Deterministic equations of motion and phase ordering dynamics

We numerically solve microscopic deterministic equations of motion for the two-dimensional straight phi(4) theory with random initial states. Phase ordering dynamics is investigated. Dynamic scaling is found and it is dominated by a fixed point corresponding to the minimum energy of random initial states.     

Two-dimensional ordering of inclusions in smectic C phase

The organization of inclusions nucleated in free standing films of smectic C (SmC) liquid crystal is investigated using polarized light microscopy. Anchoring on the inclusion boundaries induces distortions of the in-plane orientational order of the SmC phase, which drive the elastic interactions between inclusions. Such interactions show a quadrupolar character. At low concentration, the inclusions self-organize in linear or branched chain structures, while at high concentrations two-dimensional patterns appear in the film.     

On the structure of the metastable crystal phase of MBBA

The difference between the melting entropies of the stable and metastable crystal phases of MBBA may be interpreted as being due to the motions of the methoxy and n-butyl “tails” of the molecule.