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Electrospinning of polymer solutions involves self-organization of dissipative structures to order through fluctuations, providing one of the fundamental research topics in statistical physics of n...

Accurate jet diameters have been experimentally obtained during electrospinning by the light-scattering technique together with the Mie theory for cylinder scattering. Afterward, the fluid velocity...

Here, we aim to comprehend the mechanism of the order–order transition (OOT) from nonequilibrium, metastable phase to equilibrium phase. Polystyrene-block-polydimethylsiloxane (PS-PDMS) block copol...

In fibers spun from polymer solutions, we investigated self-organization of ordered shish kebabs via the cascade evolution of various dissipative structures through multistep phase transitions at multiple length scales. We used transmission electron microtomography to discover for the first time crystalline fibrils with diameters of ∼10 nm that orthogonally bridge neighboring kebabs epitaxially overgrown from shishs. The fibrils evolved during the late-stage self-organization processes of the shish kebabs. The fibrils were classified as completely bridging fibrils and pairs of broken fibrils facing each other; the broken fibrils were formed by the following two steps, first by the flow-induced burst of the bridging domains driven by Laplace pressure and subsequent crystallization involved in the burst domains. The bridging and broken fibrils were observed at interkebab distances smaller and larger than the critical length of ∼80 nm, respectively. The bridging fibrils and the cores of the broken fibrils ha...

Self-organization in nonequilibrium systems is an important research topic in the physical sciences for understanding the formation of patterns or orders in various systems, including patterns in nature. In this study, we investigated the self-organization of nanoparticles dispersed in polymer melts under applied mechanical energy imposed to mixtures that are composed of a bulk of the particle powder and a bulk of the polymer melt. Using various scattering methods that enable the exploration of structures that exist over a length scale that spans from ~0.1 nm to ~20 μm, we elucidated that the self-organized particles had hierarchical structures with various hierarchical levels as follows: primary particles (PPs), aggregates of the PPs fused together, clusters of the aggregates, and partially interdigitating mass-fractal structures built up by the clusters. The structures of the cluster and the fractal structures depend on attractive interactions between the polymers and the aggregates in given mixing conditions. We propose that the self-organization is caused by cascade evolutions of various dissipative structures, which are involved in the following energy dissipation processes driven by the deformation and flow of polymers during the mixing process. Dissipation Process I involves the fracture and flow of the particle grains in the powder, within which particles are bonded by interparticle attractive forces in air; the outer surfaces of which are in contact with the polymer matrix via polymer–particle interaction. Dissipation Process II involves the initial formation of the clusters, in which the aggregates are bound by polymers and subsequent formation of the mass-fractal agglomerates of the clusters via the diffusion-limited cluster–cluster association in the polymer matrix. The cascade structure evolutions and applied energy dissipation invoke a cascade reduction of the free energy of systems toward a minimum driven by net attractive interactions between the particles and the polymers throughout Dissipation Processes I and II. Self-organization in nonequilibrium systems composed of a bulk filler powder and a bulk polymer melt as an initial state (i) into a final ordered state (f) in applied mechanical field occurs via cascade evolution of the dissipative structures (a) to (e) accompanied by the cascade energy dissipation processes [Process (I) and Process (II)]. These processes also induce the relevant cascade changes in free energy and stress level.

We investigated the effects of the hydrogen-bonding interaction and molecular architecture on the phase and crystallization behaviors of binary copolymer blends. In blends comprising polystyrene-block-poly(ethylene oxide) (PS-b-PEO) and polystyrene-block-poly(acrylic acid) (PS-b-PAA) block copolymers, the hydrogen bonding between PEO and PAA block chains improved their miscibility so that they shared the common domains and microphase-separated against the domains composed of PS block chains, keeping their junctions at the common interfaces. However, hydrogen bonds reduced the crystallizable chain length of PEO, causing crystallization to occur within a more confined region and at a lower temperature. In the PS-b-PEO and polystyrene-graft-poly(acrylic acid) (PS-g-PAA) blends, the junctions between the PS main chain and the branched PAA block chains in PS-g-PAA were also localized at the PS-b-PEO interface with the PS main chains segregated into PS microdomains and the PAA branches hydrogen-bonded with the ...

Self-organization in nonequilibrium systems is a research topic in the statistical physics universally important for formation of patterns or orders in various systems, including nature. In this work, we investigated the self-organization processes of ordered structures via cascade evolutions of various dissipative structures through fluctuations in electrospun poly(vinyl alcohol) aqueous solutions in both mesoscopic and macroscopic length scales. The flowing jets were investigated both in situ, macroscopically with a high speed video imaging and ex situ, mesoscopically under optical and electron microscopies as a function of the polymer concentration. In the semidilute unentangled solutions, the main jet evolved a self-similar, cascade network composed of a set of the bulge and the branched subjets issued from the bulge as a building block of the network. In the semidilute entangled solutions, the main jet evolved a series of bulges elongated along the jet axis without formation of the branched subjets. ...

We investigate the formation of the ordered bicontinuous structures in a stereoregular diblock copolymer, isotactic polypropylene-block-polystyrene (iPP-b-PS), in which the minority PP block possessed isotactic configuration. This diblock displayed the conventional ordered bicontinuous double gyroid (OBDG) morphology upon heating above the crystal melting point of the iPP block from the as-cast state. The OBDG phase remained stable in the heating process up to the order–disorder transition. In the subsequent cooling process from the nearly disordered state, the OBDG phase first developed, but when the temperature was sufficiently low, an order–order transition from OBDG to the ordered bicontinuous double diamond (OBDD) phase occurred, and OBDD eventually became the dominant structure. The results attested that OBDD and OBDG represented the thermodynamically stable structure at the lower and the higher temperature, respectively, and the OBDG morphology formed in the as-cast state was metastable. The presen...

In the electrospinning process, the measurement of extension rate of the straight jet is not an easy task. In this study, the diameter profile of the tapering straight jet is determined with a laser light-scattering technique. Afterwards, the jet extension rate (e˙) is derived and used to compare with the solution-intrinsic rates, for example, the terminal relaxation rate and the Rouse relaxation rate. The extension rate of the straight jet depends on position: it is highest near the cone apex (region I) and decays to a constant value in the major jet (region II) until approaching the jet end (region III), at which the extension rate abruptly drops to nearly zero, that is, e˙I >e˙II ≫e˙III ∼ 0. The jet diameter in region III is independent of solution concentration and applied voltage, but is scaled to the flow rate with an exponent of ∼0.37. The derived exponent is consistent with a simple prediction based on the counterbalance between the stretching electric force and the compressive force induced by the air drag force. Provided that air friction becomes overwhelming at the straight jet end, the long electrified jet is likely to buckle, thereby triggering the instability of jet whipping. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

We elucidated the spatial distribution of filler particles in cross-linked poly(styrene-ran-butadiene) rubbers (SBR) developed under a typical fillers/rubbers compounding process as one of dissipative structures formed under a stress field imposed on the given system. Two types of fillers and two types of SBR were used to prepare four kinds of the fillers/rubbers composites to investigate effects of specific polymer/filler interactions on the hierarchically self-organized dissipative structures under a given processing condition. The dispersion structures of the filler particles were explored by using the combined small-angle scattering (CSAS) method, which enables the exploration of the structures existing over the wide length scale ranging from ∼6 nm to ∼20 μm. The measured CSAS profiles were analyzed by using a newly developed scattering theory on fractal structures built up by the “cluster” as their lower cutoff objects. This cluster is composed of a few aggregates, defined as the fused primary filler...

The rheological properties of poly(N-isopropylacrylamide, PNIPAM) in dimethylformamide solvent were investigated and correlated with solution electrospinnability. The jet diameter was measured by using the light scattering technique during the electrospinning in the straight jet region prior to the jet whipping. The diameter of the straight jet end is independent of the solution concentration (or viscosity within the range of 15–2000 mPa·s). Thus, the final fiber diameter df observed on the grounded collector is dominantly controlled by the jet-whipping process. According to the present PNIPAM solution and other different polymer solutions, df is correlated with the solution concentration ϕ. A master curve is constructed by using the following equation: df/df,e = (ϕ/ϕe)2.5, where df,e is the diameter of the fibers electrospun from the solutions with an entanglement concentration of ϕe, above which the specific viscosity starts to increase with ϕ according to ϕ3.7 or ϕ4.7, depending upon the given polymer/...

Exploiting the assembly of metallic nanoparticles (NPs) in their hybrids with polymers is an important task for creating new properties or functionalities via collective interactions or dynamics of the constituents. In this work, we present a detailed study of the process and mechanism of the reaction-induced hierarchical assembly of NPs in the hybrid wherein the metallic Pd NPs were synthesized and their numbers in the system increased with time by reducing the metal precursor, Pd(acac)2, originally dissolved uniformly in the solution of poly(2-vinylpyridine) (P2VP) with benzyl alcohol (BA) as a solvent and reduction agent. The time-resolved small-angle X-ray scattering (SAXS) experiment using synchrotron radiation revealed that the structural evolution process from the beginning of NP formation to the establishment of a fractal structure built up by the clusters of Pd NPs was constituted of four distinct stages, Stages 1–4, governed by the increasing overall NP volume fraction (ϕoverall) and hence by th...

The mechanism and process of the thermally induced order−order transition (OOT) of a polystyrene-block- polyisoprene diblock copolymer from cylinders on a hexagonal symmetry (hex-cyl) to spheres on a body-centered cubic symmetry (bcc-sphere) were investigated by means of time- resolved observation of high-resolution small-angle X-ray scattering (hr-SAXS) profiles obtained with a Bonse-Hart type USAXS apparatus. The USAXS apparatus enabled us to precisely study changes in the scattering peak profiles with time induced by the OOT between the two equilibrium morphologies of hex-cyl and bcc-sphere with a high resolution with respect to magnitude of scattering vector q. The peaks due to hex-cyl and bcc-sphere, which are closely located and hence overlapped one another in q-space when they are observed with conventional SAXS apparatuses, are well resolved into separated peaks with the hr-SAXS, which gave a new insight into the OOT process and mechanism as elucidated in the text.

We report a new insight into the chemical gelation process of poly(N-isopropylacrylamide) (PNiPAAm) hydrogel elucidated on the basis of the in situ observations with time-resolved Fourier-transform...

We explored in situ a “directed” self-assembly of block copolymers into a twinned body-centered cubic sphere (bcc-sphere) with a special orientation via the order–order phase transition from a specially aligned hexagonal cylinder (hex-cyl) by using time-resolved synchrotron small-angle X-ray scattering and transmission electron microscopy. We elucidated that the hex-cyl with its cylinder axis and {11} lattice plane aligned respectively parallel to the OX axis and the OXZ plane was epitaxially transformed into the twin bcc-sphere with its twin axis ⟨111⟩ and twin plane {112} having respectively the “directed orientation” parallel to the OX axis and the OXZ plane. We found that the directed self-assembly involves a three-step nucleation growth (NG) process as follows. Step I corresponds to a pretransition process, where hex-cyl undergoes the cooperative and periodic undulation of the cylinders with their pinching or bulging points being spatially arranged with the “bcc symmetry” which is attained in bcc-sph...

The cross sections of the $^{7}\mathrm{Be}(n,\ensuremath{\alpha})^{4}\mathrm{He}$ reaction for $p$-wave neutrons were experimentally determined at ${E}_{\mathrm{c}.\mathrm{m}.}=0.20--0.81\text{ }\text{ }\mathrm{MeV}$ slightly above the big bang nucleosynthesis (BBN) energy window for the first time on the basis of the detailed balance principle by measuring the time-reverse reaction. The obtained cross sections are much larger than the cross sections for $s$-wave neutrons inferred from the recent measurement at the n_TOF facility in CERN, but significantly smaller than the theoretical estimation widely used in the BBN calculations. The present results suggest the $^{7}\mathrm{Be}(n,\ensuremath{\alpha})^{4}\mathrm{He}$ reaction rate is not large enough to solve the cosmological lithium problem, and this conclusion agrees with the recent result from the direct measurement of the $s$-wave cross sections using a low-energy neutron beam and the evaluated nuclear data library ENDF/B-VII.1.

We applied a large-amplitude oscillatory shear deformation (LAOS) to polystyrene-block-polyisoprene-block-polystyrene which had nearly randomly oriented grains of body-center-cubic lattice of spherical microdomains (BCC-sphere) before applying LAOS. Mechanical and structural responses of the BCC-sphere were simultaneously measured as a function strain phase ϕ and number of oscillatory strain cycles N by means of shear stress measurements and strain-phase-resolved dynamic small-angle X-ray scattering (DSAXS). The DSAXS revealed the following pieces of evidence: (1) LAOS first leads the BCC-sphere to attain two sets of the specific orientations as defined by A- and A′-sphere and by B- and B′-sphere, where both A- and A′-sphere and B- and B′-sphere are in the mirror symmetry with respect to {112} lattice plane which is parallel to the shear plane (the OXZ-plane with the OX- and OZ-axis defined as the shear direction and vorticity or neutral axis, respectively) for A- and A′-sphere or to the OXY-plane with th...

We studied how the palladium nanoparticles, (Pd)ns, incorporated into poly(styrene)-block-poly(methyl methacylate) (PS-b-PMMA) block copolymer (bcp), alter its order–disorder transition (ODT). The (Pd)ns were incorporated into the lamellar template of PS-b-PMMA by the thermal reduction of Pd(acac)2, dissolved uniformly in the bcp before the reduction, at 230 °C where both the neat PS-b-PMMA and the PS-b-PMMA incorporated with (Pd)ns (nanocomposite) are in the disordered state. The ODT behavior of the neat bcp and the nanocomposites are investigated by small-angle X-ray scattering as a function of temperature. We found that: (i) the average size and size distribution of (Pd)ns did not change at all during the heating and cooling processes across the ODT; (ii) the incorporation of a very small amount (1 wt %) of (Pd)ns significantly increased the ODT temperature (TODT) by ∼8 °C and the lamellar spacing D by ∼1%. These trends were found to be completely opposite to those previously reported on the (Pd)ns inc...

The scattering length of a proton against a polarized neutron depends strongly on the polarization of proton spins ( P H). This dependence can be utilized for contrast variation in small angle neutron scattering (SANS). We applied this spin contrast variation technique to a silica-filled SBR rubber specimen, which is widely used for tread rubber of fuel-efficient tires. For realizing high P H, we used dynamic nuclear polarization (DNP) technique, in which large polarization of electron spin at low temperature and high magnetic field is transferred to proton spin by microwave irradiation with a tuned frequency. As this electron spin source, we doped stable radical TEMPO (2,2,6,6-tetramethyl piperidine 1-oxyl) into the rubber sample by use of a vapor sorption technique. For the TEMPO-doped rubber sample, SANS measurements were conducted at P H = −20%, 0%, and +13%, with almost fully polarized neutron beam %) with its wavelength of 6.5±0.6 A. The SANS profile clearly changed as a function of P H, which can be explained by the P H dependence of the neutron scattering length densities of the main three components (SBR, silica and zinc oxide). By a linear transformation of the profiles obtained at the three different P H values, we successfully determined the partial scattering function of silica, which reflects the aggregation of silica particles.