Muon spin rotation and relaxation experiments in the pyrochlore iridate Eu 2 Ir 2 O 7 yield a welldefined muon spin precession frequency below the metal-insulator/antiferromagnetic transition temperature T M = 120 K, indicative of long-range commensurate magnetic order and thus ruling out quantum spin liquid and spin-glass-like ground states. The dynamic muon spin relaxation rate is temperature-independent between 2 K and ∼T M and yields an anomalously long Ir 4+ spin correlation time, suggesting a singular density of low-lying spin excitations. Similar behavior is found in other pyrochlores and geometrically frustrated systems, but also in the unfrustrated iridate BaIrO 3 . Eu 2 Ir 2 O 7 may be only weakly frustrated; if so, the singularity might be associated with the small-gap insulating state rather than frustration.

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Self-assembly of ordered structures under the external fields is one of the most important and fundamental research themes in physical science of soft matters including polymers. The “shish-kebab” self-assembly is a most intriguing but fundamental crystalline superstructure formed in polymers under various flow fields. Nevertheless the mechanism of shish-kebab formation is not fully understood yet. In order to clarify the mechanisms for polymer solutions, we have investigated the flow-induced self-assembling structures evolved along a fiber spinning line for concentrated polymer solutions and proposed a new scenario of the kinetic pathway leading to shish-kebab formation and various transient structures evolved therein. The proposed pathway comprises two stages: (i) the early stage pathway before an onset of the birefringence upturn, where the flow-induced phase separation plays a dominant role on creating a series of various transient structures leading to the “sring-like structure” (denoted as “string”), all of which are hardly able to be detected by conventional SAXS, SANS, and WAXD; (ii) the late stage pathway after the onset of the birefringence upturn where the flow-induced crystallization plays a dominant role on generating bundles of stretched chains, probably via the so-called coil–stretched chain transition, within the strings grown in the early stage pathway, followed by nucleation–growth of shishs and epitaxial crystallization of kebab lamellae onto shishs from the random coils incorporated within the demixed domains which coexist with shishs within the given string. Our work therefore elucidates an important role of the flow-induced phase separation on the flow-induced shish-kebab formation.

Dynamic mechanical measurements were conducted for several kinds of ultra–high‐strength polyethylene fibers with different methyl branch contents. As is the case with conventional polyethylene materials, UHSPE fibers also exhibit α, β, and γ‐relaxation dispersions. Each relaxation process is the function of both the tensile moduli and the branch contents of UHSPE fibers. It was also found that the γ‐process of UHSPE fibers is dominated mainly by the localized molecular motion in the crystalline part, such as a dislocation mode of crystallite defects, which is very sensitive to the branching content. From the time and temperature superposition of the frequency dispersion experiments, it was found that activation energies for both the α2‐process and α3‐process increase proportionally to the methyl branch content, while the α1‐process is not so affected by the branch content. This result shows that the incorporated branch sites in the crystalline part effectively hinder the chain‐to‐chain slippage; meanwhile, they have not hindered the slippage at the grain boundary so far, which also enables us to explain the creep improvement of UHSPE fibers through branch incorporation with the same mechanism. © 1994 John Wiley & Sons, Inc.

The shear-induced concentration fluctuations in semidilute solutions comprised of ultrahigh molecular weight polyethylene (UHMWPE) as a solute and paraffin as a solvent were studied by shearsmall-angle light scattering and shear-microscopy. In steady-state shear flow, a unique anisotropic scattering pattern was found to appear when the shear rate y is increased above a critical shear rate yc. This anisotropic scattering pattern was found to be essentially identical to the "butterfly pattern" observed in high molecular weight polystyrene solutions in dioctyl phthalate. This butterfly pattern, found at temperatures higher than the equilibrium melting temperature of UHMWPE, suggests that the shearinduced concentration fluctuations or phase separation occurs in the homologous mixtures of UHMWPE and paraffin having characteristics of athermal solutions.

ABSTRACT:BC solid state high resolution NMR spectra of ultra high-molecular weight polyethylene fibers (UHF) were measured. The main narrow line is due to orthorhombic crystalline phase (ORC). Because of the high degree of crystallinity, amorphous phase signal is observed so small as the foot of the main crystalline phase signal. The small signal of monoclinic crystal phase (MCC) can be observed at lower field than the ORC signal. Signal width of MCC peak is as narrow as ORC peak. Several kinds of relaxation parameters are measured to discuss the two crystalline and intermediate phase. The crystalline phase signal can be divided into several components according to the difference in relaxation time. The signal of highly mobile component spreads over MCC and ORC signals. This component is not a crystal but its conformation is similar to that of the crystal. It may be such as oriented amorphous.

Structural development of ultra-high strength polyethylene fibers via hot-drawing processes of as-spun gel fibers was investigated by means of transmission electron microscopy. It is found that the shish-kebabs developed in both the as-spun and drawn fibers can be transformed continuously into the micro-fibril structure composed mostly of the shish structure through the hot-drawing process. The structure transformation involves a drastic decrease in diameter of the kebab plus the shish but almost no change in the shish diameter. This result suggests that the chains in the kebabs are incorporated into the shishs and consumed to extend the longitudinal dimension of the shishs during the drawing process. The proposed new deformation model well explains the relationship between the fiber morphology and their mechanical properties: the tensile strength and modulus of the fibers can be determined by the number of the shish in the fiber and the macroscopic diameter of the fiber, which are apriori determined at the spinning process.

We investigated the tensile strength and modulus of ultrahigh‐strength polyethylene (UHSPE) fibers obtained by using the special two‐step‐drawing process of as‐spun fiber (ASFs) which were prepared by the so‐called gel‐spinning method. We have found that the higher the ASF's spinning speed is, the higher the attainable tensile strength σf and modulus E are. For all the fibers drawn from ASFs with various spinning speed except for 120 m/min, we have found a master curve for the inverse of σf which is plotted as a function of T1/4E−1/2, where T is the linear density of the drawn fibers, in consistent with the Griffith theory: a thicker fiber obtained with a lower spinning speed exhibits lower strength, although all the AFSs possess the same value of E. This also suggests that a thicker fiber contains more defects which would lead to the Griffith‐type crack propagation breakage. Moreover, from morphological observation of ASFs under transmission electron microscopy, the ASF obtained at a relatively low spinning speed possesses a heterogeneous cross‐sectional morphology, whereas that obtained at relatively high spinning speed possesses a relatively homogenous morphology. We propose that this morphological evidence may account for the experimental findings of the behavior of the mechanical properties described above. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2639–2652, 2005