Chain-Level Analysis of Reinforced Polyethylene through Stretch-Induced Crystallization.

Herein, we propose a large-scale simulation approach to perform the stretch-induced crystallization of entangled polyethylene (PE) melts. Sufficiently long (1000 ns) united-atom molecular dynamics (UAMD) simulations for 16000 chains of 1000 consecutive CH2 united-atom particles under periodic boundary conditions were performed to achieve the crystallinity observed in experiments. Before the isothermal crystallization process, we applied uniaxial stretching as pre-elongation to the embedded strain memory on the entangled PE melts. We confirmed significant differences in the morphologies of crystal domains and scattering patterns for pre-elongation ratios of 400% and 800%. The obtained scattering patterns were consistent with the experimental results. Uniaxial stretching MD simulations revealed that the elastic modulus at 800% pre-elongation was stronger than that at 400% pre-elongation. From this observation, we can derive the structure-property relationship, wherein the magnitude of the pre-elongation governs the crystal domain structures and mechanical properties.

Structure-Property Correlation in Natural Rubber Nanocomposite Foams: A Comparison between Nanoclay and Cellulose Nanofiber Used as Nanofillers.

Nanocomposite foams of natural rubber (NR) with 5 phr of two kinds of nanofillers, nanoclay (NC) and cellulose nanofiber (CNF), were produced using the latex mixing method and foaming with azodicarbonamide. The effect of the nanofiller on the structure and mechanical properties of NR foams was investigated through SEM, TEM, tensile tests, WAXD, and compression set measurements. Smaller cells with a narrower distribution were attained in the NC/NR foam when compared to the NR and CNF/NR foams, and the expansion ratio was larger due to the suppression of the shrinkage in the NC/NR foam. The foaming of the NR nanocomposites reduced the size of the filler aggregates and improved the dispersion and alignment of nanofillers in the cell walls. The addition of NC and CNF enhanced the tensile strength of the NR foam by 139% and 62%, respectively, without sacrificing the excellent strain of the NR, due to the acceleration of the strain-induced crystallization and small size of the filler aggregates. The compression set of the NR foam could also be reduced in the NC/NR foam compared with the NR and CNF/NR foams.

Phase-Separated Structure of NBR/PVC Blends with Different Acrylonitrile Contents Investigated Using STEM-EDS Mapping Analysis.

We investigated the phase-separated structure of nitrile butadiene rubber (NBR)/polyvinyl chloride (PVC) blends with different acrylonitrile (AN) contents in the NBR, using dynamic mechanical analysis measurements and scanning-transmission-electron-microscopy (STEM)-energy-dispersive-X-ray-spectroscopy (EDS) elemental analysis. Two separate sharp tan δ peaks were observed in the blend at the lower AN content of 18.0%, whereas a broad peak was observed in the blends with the higher AN contents of 29.0 and 33.5%, due to the increase in miscibility, as expected from the decrease in the solubility parameter difference with the increasing AN content. The STEM-EDS elemental analysis for the concentration distribution showed that the NBR was mixed in the large PVC domains with a diameter of several micrometers, and the excluded PVC existed around the interface of the domain-matrix phases in the blend with the lower AN content, whereas small domains with a diameter of several tens of nanometers were dispersed in the blend with the higher AN content. The concentration difference in PVC between the PVC domain and the NBR matrix became smaller with increasing miscibility as the AN content increased although the blends contained the same PVC content of 40 wt%.

Partial Miscibility and Concentration Distribution of Two-Phase Blends of Crosslinked NBR and PVC.

We found that the blends of nitrile butadiene rubber (NBR) and polyvinyl chloride (PVC) exhibited lower critical solution temperature (LCST)-type phase behavior in which a single-phase blend tends to phase separate at elevated temperatures when the acrylonitrile content of NBR was 29.0%. The tan δ peaks, which originated from the glass transitions of the component polymers measured by dynamic mechanical analysis (DMA), were largely shifted and broader in the blends when the blends were melted in the two-phase region of the LCST-type phase diagram, suggesting that NBR and PVC are partially miscible in the two-phase structure. The TEM-EDS elemental mapping analysis using a dual silicon drift detector revealed that each component polymer existed in the partner polymer-rich phase, and the PVC-rich domains consisted of aggregated small PVC particles the size of several ten nanometers. The partial miscibility of the blends was explained by the lever rule for the concentration distribution in the two-phase region of the LCST-type phase diagram.

Reinforcement Behavior of Chemically Unmodified Cellulose Nanofiber in Natural Rubber Nanocomposites.

We investigated the reinforcement behavior of small amounts of chemically unmodified cellulose nanofiber (CNF) in eco-friendly natural rubber (NR) nanocomposites. For this purpose, NR nanocomposites filled with 1, 3, and 5 parts per hundred rubber (phr) of cellulose nanofiber (CNF) were prepared by a latex mixing method. By using TEM, a tensile test, DMA, WAXD, a bound rubber test, and gel content measurements, the effect of CNF concentration on the structure-property relationship and reinforcing mechanism of the CNF/NR nanocomposite was revealed. Increasing the content of CNF resulted in decreased dispersibility of the nanofiber in the NR matrix. It was found that the stress upturn in the stress-strain curves was remarkably enhanced when the NR was combined with 1-3 phr CNF, and a noticeable increase in tensile strength (an approximately 122% increase in tensile strength over that of NR) was observed without sacrificing the flexibility of the NR in the NR filled with 1 phr CNF, though no acceleration in their strain-induced crystallization was observed. Since the NR chains were not inserted in the uniformly dispersed CNF bundles, the reinforcement behavior by the small content of CNF might be attributed to the shear stress transfer at the CNF/NR interface through the interfacial interaction (i.e., physical entanglement) between the nano-dispersed CNFs and the NR chains. However, at a higher CNF filling content (5 phr), the CNFs formed micron-sized aggregates in the NR matrix, which significantly induced the local stress concentration and promoted strain-induced crystallization, causing a substantially increased modulus but reduced the strain at the rupture of the NR.

Comparative Structure-Property Relationship between Nanoclay and Cellulose Nanofiber Reinforced Natural Rubber Nanocomposites.

Natural rubber (NR) nanocomposites reinforced with five parts per hundred rubber (phr) of two different nano-fillers, i.e., nanoclay (abbrev. NC) and cellulose nanofiber (abbrev. CNF), were prepared by using latex mixing approach, followed by mill-compounding and molding. The morphology, stress-strain behavior, strain-induced crystallization, and bound rubber of the NR nanocomposites were systematically compared through TEM, tensile test, WAXS, DMA, and bound rubber measurement. The aggregated CNFs were observed in the NR matrix, while the dispersed nanosized clay tactoids were detected across the NR phase. The reinforcement effects of NC and CNF were clearly distinct in the NR nanocomposites. At the same nano-filler content, the addition of NC and CNF effectively accelerated strain-induced crystallization of NR. The high tensile strength obtained in the NC-filled NR nanocomposite was attributed to strain-induced crystallization of NR accelerated by well-dispersed NC. However, the larger tensile modulus and low strain for the CNF-filled NR were related to the formation of immobilized NR at the interface between CNF aggregate and NR. The immobilization effect of NR at the CNF surface offered by a mutual entanglement of CNF aggregate and NR chain led to local stress concentration and accelerated strain-induced crystallization of CNF/NR nanocomposite. From the present study, the NR nanocomposites combined with 5 phr CNF shows high-tensile modulus and acceptable breaking tensile stress and strain, suggesting the application of CNF/NR based nanocomposite in automotive and stretchable sensors for next-generation electronic devices.

Two-Stage Evolution of Gamma-Phase Spherulites of Poly (Vinylidene Fluoride) Induced by Alkylammonium Salt.

We investigated the evolution of the γ-phase spherulites of poly(vinylidene fluoride) (PVDF) added to 1 wt% of tetrabutylammonium hydrogen sulfate during the isothermal crystallization at 165 °C through polarized optical microscopy and light scattering measurements. Optically isotropic domains grew, and then optical anisotropy started to increase in the domain to yield spherulite. Double peaks were seen in the time variation of the Vv light scattering intensity caused by the density fluctuation and optical anisotropy, and the Hv light scattering intensity caused by the optical anisotropy started to increase during the second increase in the Vv light scattering intensity. These results suggest the two-stage evolution of the γ-phase spherulites, i.e., the disordered domain grows in the first stage and ordering in the spherulite increases due to the increase in the fraction of the lamellar stacks in the spherulite without a change in the spherulite size in the second stage. Owing to the characteristic crystallization behavior, the birefringence in the γ-phase spherulites of the PVDF/TBAHS was much smaller than that in the α-phase spherulites of the neat PVDF.

High-Strength Heat-Elongated Thermoplastic Polyurethane Elastomer Consisting of a Stacked Domain Structure.

We found that a high-strength elastomer was obtained by the heat elongation of a thermoplastic polyurethane (TPU) film consisting of a high content of crystalline hard segments (HS). The stress upturn continuously increased with the elongation ratio without a decrease in the strain recovery by heat elongation, i.e., the stress at break of a quenched TPU film was increased from 55 to 136 MPa by heat elongation at an elongation ratio of 300%. The results of small-angle X-ray scattering, DSC, and AFM observations revealed that: (1) anisotropically shaped HS domains were stacked at a nanometer scale and the longer direction of the HS domains was arranged perpendicular to the elongated direction due to the heat elongation, (2) the densification of the HS domains increased with increases in the elongation ratio without a significant increase in the crystallinity, and (3) the stacked domain structure remained during the stretching at 23 °C. Thus, the strengthening of the elongated TPU might be attributed to the densification of the HS domains in the stacked structure, which prevents the fracture of the HS domains during the stretching.

Effects of sterol derivatives in cationic liposomes on biodistribution and gene-knockdown in the lungs of mice systemically injected with siRNA lipoplexes.

Cationic liposomes can be intravenously injected to deliver short interfering (si)RNAs into the lungs. The present study investigated the effects of sterol derivatives in systemically injected siRNA/cationic liposome complexes (siRNA lipoplexes) on gene­knockdown in the lungs of mice. Cationic liposomes composed of 1,2­dioleoyl­3­trimethylammonium­propane or dimethyldioctadecylammonium bromide (DDAB) were prepared as a cationic lipid, with sterol derivatives such as cholesterol (Chol), ß­sitosterol, ergosterol (Ergo) or stigmasterol as a neutral helper lipid. Transfected liposomal formulations composed of DDAB/Chol or DDAB/Ergo did not suppress the expression of the luciferase gene in LLC­Luc and Colon 26­Luc cells in vitro, whereas other formulations induced moderate gene­silencing. The systemic injection of siRNA lipoplexes formulated with Chol or Ergo into mice resulted in abundant siRNA accumulation in the lungs. In comparison, systemically injected DDAB/Chol or DDAB/Ergo lipoplexes of Tie2 siRNA effectively increased the suppression of the Tie2 mRNA expression in the lungs of mice. These findings indicated that DDAB/Chol and DDAB/Ergo liposomes could function as vectors for siRNA delivery to the lungs.

UCST Type Phase Boundary and Accelerated Crystallization in PTT/PET Blends.

We investigated the structure development and crystallization kinetics in the blends of poly(trimethylene terephthalate) (PTT) and poly(ethylene terephthalate) (PET) by polarized optical microscopy and light scattering. The crystallization of the blend was found to be faster and the size of the spherulites was much smaller than those of the neat component polymers by melt crystallization at low temperature of 180 °C. The discontinuous gap of the crystallization time with temperature was seen in the blends, suggesting phase transition at the temperature Ttr; e.g., the Ttr of the 60/40 PTT/PET was 215 °C. The crystallization was accelerated due to enhancement of the nucleation rate, and interconnected tiny spherulites were obtained at the temperature below the Ttr. The accelerated crystallization and the development of the interconnected structure might be attributed to the liquid-liquid phase separation via spinodal decomposition, due to existence of the upper critical solution temperature (UCST) type phase boundary.

Preparation of epoxy resins derived from lignin solubilized in tetrabutylphosphonium hydroxide aqueous solutions.

Organic onium hydroxide aqueous solutions (OHAS) are demonstrated to be potential solvents for the dissolution of lignin and its epoxidation. A series of OHAS has been assessed in terms of the solubility of soda lignin (SL) and Klason lignin (KL), which are moderately and rarely soluble in NaOH aq. soln., respectively. Tetrabutylphosphonium hydroxide ([P4444]OH) aqueous solution was found to exhibit a highest solubility, specifically 40 wt% of SL and 3.0 wt% of KL. The superior solubility of OHAS is comprehended to be due to weak interactions between OH anions and phosphonium cations, and hence OH anions interact effectively with lignin. Epoxidation of SL was achieved by simply adding epichlorohydrin to [P4444]OH aq. dissolving SL. Films of epoxidized SL were prepared by thermal curing with the aid of a crosslinking agent, and the films were found to possess high thermal stability of >250 °C and excellent ductility. The thermal and mechanical properties were controllable by the concentration of [P4444]Cl as an additive.

Evolution of Filament-Shaped Porous Structure in Polycarbonate by Stretching under Carbon Dioxide.

We found that a filament-shaped porous structure with periodic distance was obtained in polycarbonate for optical disk grade (OD-PC) film by stretching under compressed carbon dioxide (CO2). The evolution of the characteristic porous structure was investigated by in situ observation during the stretching under compressed CO2 and the optical microscopic observation of the stretched specimen. The voids were obtained under high CO2 pressure as in the case of elevated temperature, suggesting that the evolution of the voids was caused by crazing due to chain disentanglement by accelerated molecular motion owing to the plasticization effect of CO2. The filament-shaped voids were initiated at around the yielding point and increased continuously by nucleation in the matrix around the surface of the pre-existing voids. The shape of the voids did not change to an ellipsoidal one during stretching due to suppression of the craze opening by the hydrostatic pressure effect. The stretching of the CO2-absorbed depressurized OD-PC revealed that the initiation of the voids was not only caused by the plasticization effect, but the hydrostatic pressure effect was also required.

Structural Evolution of Two-Phase Blends of Polycarbonate and PMMA by Simultaneous Biaxial Stretching.

We investigated the structural evolution of the two-phase blends of polycarbonate (PC) and poly(methyl methacrylate) (PMMA) at various blend compositions by simultaneous biaxial stretching, using optical microscopy and SEM observation. The spherical PMMA domains and PC matrix of 30/70 PC/PMMA were enlarged uniformly at the all in-plane direction, while the anisotropic-shaped co-continuous structure in 50/50 PC/PMMA was deformed to a crosshatched structure by the in-plane bimodal orientation. In 70/30 PC/PMMA, the phase inversion was found to occur by simultaneous biaxial stretching; that is, the spherical PMMA domains were changed to a crosshatched matrix by the in-plane bimodal orientation due to coalescence of the PMMA domains during the stretching. Owing to the phase inversion, the surface hardness estimated by the pencil hardness test became harder, from 2B to 2H, increasing the strain from 1.0 to 2.0.

Synthesis of a Three-Bladed Propeller-Shaped Triple [5]Helicene.

Three-bladed propeller-shaped triple [5]helicene was synthesized using eliminative and oxidative photocyclization reactions, which proceeded in 37 and 63% yields, respectively. Chromatographic purification gave a mixture of diastereomers, and the PPM and PMM isomers were gradually converted to the thermodynamically more stable PPP and MMM isomers at room temperature. The activation parameters for the racemization of the PPP and MMM isomers were determined, and the structure of the triple [5]helicene was determined by X-ray crystallographic analysis.

Significant correlation between refractive index and activity of mitochondria: single mitochondrion study.

Measurements of refractive indices (RIs) of intracellular components can provide useful information on the structure and function of cells. The present study reports, for the first time, determination of the RI of an isolated mitochondrion in isotonic solution using retardation-modulated differential interference contrast microscopy. The value was 1.41 ± 0.01, indicating that mitochondria are densely packed with molecules having high RIs. Further, the RIs of each mitochondrion were significantly correlated with the mitochondrial membrane potential, an index of mitochondrial activity. These results will provide useful information on the structures and functions of cells based on the intracellular distribution of RIs.