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Behavior of the phase transition of an ionic liquid, [Cn-mim][PF6], has been investigated under pressures up to 1.0 GPa by using a high-pressure differential thermal analysis (DTA) apparatus. The T versus P phase diagrams of [BMIM][PF6] and [EMIM][PF6] are constructed. The DTA curve of [BMIM][PF6] shows one endothermal valley in heating course at each given pressure, which indicates that a simple phase transition from solid to liquid has taken place under high pressure and that the melting point is an increase function of pressure. However, the DTA curve of [EMIM][PF6] shows two endothermal valleys in the heating course within the tested pressure range, implying that there may exist another phase. After treatment of [EMIM][PF6] at different temperatures under high pressure, the structures of the recovered samples are also investigated by wide-angle x-ray scattering. By considering the results above, it indicates that another crystalline phase exists between the solid and liquid of [EMIM][PF6]. [ABSTRACT FROM AUTHOR]

The morphology of a highly asymmetric double crystallizable poly([variant_greek_epsilon]-caprolactone-b-ethylene oxide) (PCL-b-PEO) block copolymer has been studied with in situ simultaneously small and wide-angle x-ray scattering as well as atomic force microscopy. The molecular masses Mn of the PCL and PEO blocks are 24 000 and 5800, respectively. X-ray scattering and rheological measurements indicate that no microphase separation occurs in the melt. Decreasing the temperature simultaneously triggers off a crystallization of PCL and microphase separation between the PCL and PEO blocks. Coupling and competition between microphase separation and crystallization results in a morphology of PEO spheres surrounded by PCL partially crystallized in lamella. Further decreasing temperature induces the crystallization of PEO spheres, which have a preferred orientation due to the confinements from hard PCL crystalline lamella and from soft amorphous PCL segments in different sides. The final morphology of this highly asymmetric block copolymer is similar to the granular morphology reported for syndiotactic polypropylene and other (co-) polymers. This implies a similar underlying mechanism of coupling and competition of various phase transitions, which is worth further exploration. [ABSTRACT FROM AUTHOR]

The structure of the Ca−alginate junction zones was investigated with X-ray scattering on gels prepared with different methods. Fiber diffraction reveals the popular egg-box model may not be the only possible structure for the junction zones. The (001) reflection, which should be extinguished due to 2/1 helical conformation in the egg-box model, was observed. This was further confirmed by the measurements on Ca−alginate gel beads prepared at different pH where large pieces were formed through a relatively slow process, which leads to a higher crystallinity and a more perfect ordering. The results suggest a 3/1 helical conformation is more proper for Ca−alginate gels formed slowly. This does not exclude the possibility for the 2/1 helical conformation in fast gelatinized Ca−alginate in which the 2/1 helix is a metastable form. Comparing the X-ray scattering results of the fresh, dehydrated, and rehydrated gels, a reversible aggregation of junction zones is found during dehydration and rehydration. The different stabilities of initial bonds and bonds formed during drying are speculated to be the contribution of MG block or short G blocks in the junction zones. [ABSTRACT FROM AUTHOR]

Enhancing the dynamic asymmetry between liquid-like and solid-like components leads to spontaneous segregation. As a typical example, the binary blends of stretched and free guest polymers were investigated by our dynamic Monte Carlo simulations. The results evidenced an entropic driving force for the strain-induced segregation between two components, similar to that for Onsager's lyotropic liquid crystals. In addition, with the decrease of strain rates, its competition with strain-induced crystal nucleation results in variable compositions in crystal precursors. The scenario helps to settle down the controversial arguments on the flow-induced precursors of shish-kebab crystallites in the melt. [ABSTRACT FROM AUTHOR]

Flow-induced crystallization (FIC) of polymers is a long-standing, industrial relevant, nonequilibrium thermodynamic challenge. Thanks to the development of in situ time and spatial resolved techniques like rheology and synchrotron radiation X-ray scattering, substantial progress on the understanding of FIC has been achieved in past 20 years. In this Perspective, we first discuss some recent modifications and improvements on early coarse-grained approaches like the coil-stretch transition model for shish formation and the entropic reduction model for the enhancement of nucleation rate. Then breaking out the two-phase model of classical nucleation theory, flow-induced coil-helix transition, density fluctuation or phase separation, and isotropic-nematic transition are considered as intermediate orders in FIC. Establishing flow morphology and phase diagrams is essential for revealing the nonequilibrium nature of FIC, which will serve as structural roadmap for the processing of high performance polymer products. [ABSTRACT FROM AUTHOR]

Ionic effects in aqueous solution of macro-ions showing specificity and unconventional characters, respectively, receive a lot of interests recently; however, the complexity of specific ion effects in unconventional phenomena remains ambiguous. In this study, the effects of univalent ions on aggregation of supra-molecular nano-fibrils with charged carboxylate groups on the surface as a prototype of macro-ions are investigated by Small Angle X-ray Scattering (SAXS) in aqueous solutions of alkaline metal chlorides. It is found that the columnar bundles of charged fibrils are expanded in certain salt concentration range contradicting the conventional screening effects of salts. The degree of expansion is dominated by cations as Na+ induces drastic effects in comparison to rather gentle changes from K+ and Cs+. The specific cations effects observed by SAXS correlate with the pH behavior of the solutions, an indicator of surface charge, or number of carboxylate groups along the supra-molecular fibrils. It is postulated that while Na+ with stronger affinity to carboxylates apparently reduces the surface charge, K+ and Cs+ only weakly interact with carboxylates and induce minor changes, accounting for the cation-sensitive aggregation behavior of fibrils observed by SAXS. By probing the bundling aggregation of charged supra-molecular nano-fibrils in salty water, we provide direct evidence of specific counter-ion effects in unusual expansion caused by univalent salts. [ABSTRACT FROM AUTHOR]

Load-bearing biological tissues, such as muscles, are highly fatigue-resistant, but how the exquisite hierarchical structures of biological tissues contribute to their excellent fatigue resistance is not well understood. In this work, we study antifatigue properties of soft materials with hierarchical structures using polyampholyte hydrogels (PA gels) as a simple model system. PA gels are tough and self-healing, consisting of reversible ionic bonds at the 1-nm scale, across-linked polymer network at the 10-nm scale, and bicontinuous hard/soft phase networks at the 100-nm scale. We find that the polymer network at the 10-nm scale determines the threshold of energy release rate G0 above which the crack grows, while the bicontinuous phase networks at the 100-nm scale significantly decelerate the crack advance until a transition Gtran far above G0.In situ small-angle X-ray scattering analysis reveals that the hard phase network suppresses the crack advance to show decelerated fatigue fracture, and Gtran corresponds to the rupture of the hard phase network. [ABSTRACT FROM AUTHOR]

As a strategy for regulating entropy, thermal annealing is a commonly adopted approach for controlling dynamic pathways in colloid assembly. By coupling DNA strand-displacement circuits with DNA-functionalized colloid assembly, we developed an enthalpy-mediated strategy for achieving the same goal while working at a constant temperature. Using this tractable approach allows colloidal bonding to be programmed for synchronization with colloid assembly, thereby realizing the optimal programmability of DNA-functionalized colloids. We applied this strategy to conditionally activate colloid assembly and dynamically switch colloid identities by reconfiguring DNA molecular architectures, thereby achieving orderly structural transformations; leveraging the advantage of room-temperature assembly, we used this method to prepare a lattice of temperaturesensitive proteins and gold nanoparticles. This approach bridges two subfields: dynamic DNA nanotechnology and DNA-functionalized colloid programming. [ABSTRACT FROM AUTHOR]

Combining a homemade film blowing machine and an in situ synchrotron radiation source with small- and wide-angle X-ray scattering (SAXS and WAXS) capability, an investigation of film blowing of polyethylene (PE) has been studied. From the die exit to the positions above the frost line, four zones defined with different structural features are observed with SAXS and WAXS measurements. In zone I, precursor and crystal structures emerge from the polymer entanglement network during cooling and extension, which lead to the formation of a deformable crystal-cross-linked network at the boundary between zones I and II. The occurrence of the crystal-cross-linked network enhances the effective chain stretching during further deformation in zone II. Crystallization is largely accelerated, which generates crystals with high orientation. Further increasing the crystallinity results in the deformable crystal-cross-linked network transforming into a nondeformable crystal scaffold at the frost line (the boundary between zones II and III), which stabilizes the bubble and prevents further deformation. In zones III and IV, the scaffold and the entire sample are gradually filled up by crystals, respectively. Interestingly, increasing the take-up ratio (TUR) does not influence the critical crystallinity (χI-II) for the formation of the deformable crystal-cross-linked network, while the crystallinity (χf) at the frost line or for the formation of nondeformable scaffold does vary with TUR. This suggests that the former (χI-II) is mainly controlled by molecular parameters, while the latter (χf) is determined by both processing and molecular parameters of PE material. [ABSTRACT FROM AUTHOR]

The stretch-induced coil-helix transition (CHT) of isotactic polypropylene (iPP) was studied with full-atom molecular dynamics (MD) simulations during the uniaxial stretch process. The results show that imposing stretch induces CHT, which increases both the content and the average length of helices. As strain exceeding a certain value, long helices initially not presented in melt start to emerge, which mainly follow a kinetic pathway of merging adjacent short helices, while overstretch at large strain leads to the helix-extended coil transition. Based on statistics on the distribution of helical length and theoretical calculation, stretch is found to reduce free energy gap for CHT. At small strain, the single-chain model is sufficient to account stretch-induced CHT for the formation of short helices, but the gap reduction is mainly contributed by intrachain energy rather than entropy, which is different from current theories for stretch-induced CHT. While the formation of long helices at large strain requires interchain cooperative interactions, which is accompanied by the formation of helix-rich clusters. Additionally, we found that the content of helices with odd atoms in backbone is higher than their even counterparts, which exhibits an odd-even effect due to their corresponding helical lengths. [ABSTRACT FROM AUTHOR]

The effects of temperature on the nonlinear mechanical behaviors of hard-elastic isotactic polypropylene films are systematically studied with in-situ ultrafast synchrotron radiation small- and wide-angle X-ray scattering techniques (SAXS/WAXS) during uniaxial tensile deformation at temperatures from 30 to 160 °C. Based on the mechanical behaviors and structural evolutions in strain-temperature two-dimensional space, three temperature regions (I, II, and III) are clearly defined with the α relaxation temperature (Tα ≈ 80 °C) and the onset of melting temperature (Tonset ≈ 135 °C) as boundaries, where different mechanisms dominate the nonlinear deformations after yield. In region I, microstrain in lamellar stacks εm obtains an accelerated increase after yield and reaches a value significantly larger than corresponding macrostrain ε, during which neither slipping, melting, nor cavitation occurs. We propose stress-induced microphase separation of interlamellar amorphous to be responsible to the hyperelastic behavior in region I. Above Tα in region II, due to reduced cohesive strength and enhanced chain mobility, the irreversible reduction of crystallinity and the formation of slender cavities suggest that crystal slipping overwhelms microphase separation and plays the major role in nonlinear deformation, during which chains in lamellar crystals are pulled out and recrystallize into nanofibrillar bridges. In region III above Tonset, melting-recrystallization dictates the nonlinear deformation. A schematic roadmap for structural evolution is constructed in strain-temperature space, which may guide the processing of microporous membranes for lithium battery separators as well as other high performance polymer fibers and films. [ABSTRACT FROM AUTHOR]

Adding silica nanofiller in silicone rubber can toughen the matrix 3 orders in terms of fracture energy, which is far larger than most other nanofiller-rubber systems. To unveil the astonishing toughening mechanism, we employ in situ synchrotron radiation X-ray nanocomputed tomography (Nano-CT) technique with high spatial resolution (64 nm) to study the structural evolution of silica nanofiller in silicone rubber matrix at different strains. The imaging results show that silica nanofiller forms three-dimensional connected network, which couples with silicone chain network to construct a double-network structure. Stress-induced phase separation between silica nanofiller and silicone polymer chain networks is observed during tensile deformation. Unexpectedly, though the spatial position and morphology of nanofiller network changes greatly at large strains, the connectivity of nanofiller network shows negligible reduction. This indicates that nanofiller network undergoes destruction and reconstruction simultaneously, during which silica nanofiller serves as reversible high functionality cross-linker. The reversible bonding between silica nanofiller and silicone rubber or between nanofiller particles can dissipate mechanical energy effectively, which may account for the 3 orders enhancement of toughness. [ABSTRACT FROM AUTHOR]

Temperature effects on deformation behaviors of extracted ultrahigh molecular weight polyethylene (UHMWPE) precursor fibers are studied with the in situ synchrotron radiation wide-angle X-ray scattering technique (WAXS) during tensile deformation at temperatures from 25 to 130 °C. The structural and mechanical evolution behaviors during tensile deformation can be divided into four temperature regions with boundaries located at temperatures of αI and αII relaxations and the onset of melting, respectively, which reveal that the deformation behaviors of polymer crystals are determined by the interplay between intrinsic structural dynamic or chains mobility and external stress field. Irrespective of temperature, yield and strain-softening proceed via partial melting while crystal slip via cutting crystal planes occurs in the strain-hardening zone. Finally we construct morphological diagrams containing crystallinity, crystal size, and orientation in temperature-strain space, which may serve as a roadmap for UHMWPE fibers processing. [ABSTRACT FROM AUTHOR]

Using a pressuring and shearing device (PSD), we explored the simultaneous effects of pressure and flow on β-crystal formation. Interestingly, pressure plays a versatile role in β-crystal formation in isotactic polypropylene (iPP) mixed with β-nucleating agent (β-NA) when a flow field exists simultaneously. At a low pressure (5 MPa), a mass of β-crystals can be obtained over the entire range of applied shear rates (0.0-24.0 s-1). As the pressure increases (50-100 MPa), a weak shear flow (3.2 s-1) can profoundly suppress the β-crystal formation. When elevating the pressure to 150 MPa, β-crystals cannot be generated. The pressure and flow window to produce β-crystals in iPP mixed with β-NA were successfully summarized for the first time. The diversified β-crystal formation behaviors in iPP mixed with β-NA under the simultaneous effects of pressure and shear flow were well elucidated by combining classical nucleation theory and the growth of different crystalline phases. Our current work lays a solid foundation to tailor β-crystals in iPP mixed with β-NA in practical processing and thus to optimize the mechanical properties of iPP products. [ABSTRACT FROM AUTHOR]

The sequence and coupling of intra- and interchain orderings in flow-induced crystallization (FIC) of partially cross-linked isotactic polypropylene (iPP) is studied with in situ Fourier transform infrared spectroscopy (FTIR) and synchrotron radiation X-ray scattering techniques, which reveal that multiscale structural intermediates emerge prior to the onset of crystallization. Upon imposing flow, intrachain conformational ordering or coil-helix transition (CHT) occurs first, which is directly correlated with external stress. As helical content is built up at large strain, density fluctuation happens, and sufficient long helices may result in orientation ordering before FIC. The results demonstrate that stress induced intrachain CHT is the essential structural intermediate in FIC, which can be further coupled with interchain orientation and density providing either helical content or length meets the criterions for the phase transitions. We propose that coupling among external stress, intrachain conformational, and interchain orientation and density orderings to be the molecular mechanism for FIC of polymer forming helical structures. [ABSTRACT FROM AUTHOR]

We demonstrate the use of a pump-probe setup based on two mid-infrared quantum cascade lasers (QCLs) to investigate the melting and crystallization of materials through resonant absorption. A combination of pump and probe beams fulfills the two-color synchronous detection. Furthermore, narrow linewidth advances the accuracy of measurements and the character of broad tuning range of QCLs enables wide applications in various sample and multiple structures. 1-Eicosene was selected as a simple model system to verify the feasibility of this method. A pulsed QCL was tuned to the absorption peak of CH2 bending vibration at 1467 cm-1 to resonantly heat the sample. The other QCL in continuous mode was tuned to 1643 cm-1 corresponding the C=C stretching vibration to follow the fast melting dynamics. By monitoring the transmission intensity variation of pump and probe beams during pump-probe experiments, the resonant absorption induced fast melting and re-crystallization of 1-Eicosene can be studied. Results show that the thermal effect and melting behaviors strongly depend on the pump wavelength (resonant or non-resonant) and energy, as well as the pump time. The realization and detection of melting and recrystallization can be performed in tens of milliseconds, which improves the time resolution of melting process study based on general mid-infrared spectrum by orders of magnitude. The availability of resonant heating and detections based on midinfrared QCLs is expected to enable new applications in melting study. [ABSTRACT FROM AUTHOR]

By combining extensional rheological and in situ small-angle neutron and synchrotron X-ray scattering (SANS, SR-SAXS) techniques, the correlation between chain deformation and morphology of nucleus in a lightly cross-linked deuterated PE (D-PE)/hydrogenated PE (H-PE) blend has been studied at different draw ratios. The deformation of molecular chain obtained by SANS shows that shish forms at a rather small chain deformation of about 1.3, which does not support either coil-stretch transition or the simple stretch network model. Combining these data with the SAXS results, we speculate that the conformation ordering couples with density, instead of single chain conformation, is the key factor for shish formation. Meanwhile, due to the different alignment of the center of mass of the stretched network in samples with different draw ratios, a periodic concentration modulation of D-PE appears after crystallization of the samples stretched to the hardening zone, which, however, does not occur under the small draw ratio. [ABSTRACT FROM AUTHOR]

The room-temperature stretching process of polypropylene annealed film with row-nucleated crystalline structure was studied by in-situ small-angle X-ray scattering (SAXS) setup and off-line wide-angle X-ray scattering (WAXS), temperature-modulated differential scanning calorimetry (TMDSC) and stress–strain curves testing. The formation process of initial connecting bridges and pores was clarified. For the annealed film, except for the initial lamellae structure, the recrystallized part formed by the melting and crystallization of imperfect crystals during annealing, tie chains connecting the lamellae structure among the amorphous region, secondary crystals from the crystallization of tie chains during annealing and daughter crystals from the special cross-hatched crystalline structure of PP coexist. It was found that 10% stretching lead to the pronounced increase of long period and the appearance of a few initial connecting bridges. The stretching of daughter crystal and recrystallized part contributed to the formation of initial bridges. At stretching ratio of 30%, uniform distributed connecting bridges were observed and the stretched film showed maximum structure periodicity. At this stretching ratio, except for the stretching of daughter crystal, the stretching of tie chains and secondary crystals within the amorphous region lead to the formation of more connecting bridges. At higher stretching ratios into the strain-hardening region and beyond the second yield point, except for the stretching of the above mentioned crystalline and amorphous structure, the stretching of mother lamellae occurred and lamellae deformation was inevitable, resulting in lower structure periodicity. During room-temperature stretching, the pores were formed progressively and the stretching ratio of 30%, situated at the transition point from plastic plateau to strain-hardening region in the stress–strain curves, was appropriate for the initiation of pores. [ABSTRACT FROM AUTHOR]

The influence of mixing of iPB-1/iPP blend on the polymorphism of iPB-1 under processing-relevant conditions is studied with emphasis on the competition between the thermodynamically stable form I' crystal and the kinetically favored form II. In situ optical microscopy measurements reveal that the upper critical solution temperature (UCST) of iPB-1/iPP blend locates in the range of 180-200 °C. Unexpectedly, by quenching mixed iPB-1/iPP melt down to temperatures below UCST and melting point, form I/I' can be produced directly which is further identified as form I' by temperature-dependent WAXS and DSC. The formation of form I' is promoted by increasing the annealing time above UCST, while is suppresses by raising the quenching temperature. In addition, the crystallization of iPP also displays a similar trend as iPB-1 does. The correlated crystallization of each constituent with dependence on the initial mixing degree suggests that the crystallization behavior of the binary blends is determined by the interplay between simultaneous processes concomitant with the liquid-solid transition. The experimental results reveal the possibility to modify the crystallization pathway of iPB-1 in iPB-1/iPP blend through the mixing degree which is initially controlled by annealing but is subject to evolve during the subsequent thermal treatment. Possible mechanisms are discussed including the roles of phase separation and concentration fluctuation in crystallization. [ABSTRACT FROM AUTHOR]

The crystallization of poly(ethylene oxide) (PEO)-sodium iodine (NaI) composites is investigated by differential scanning calorimetry (DSC), extensional rheology, and in situ small-angle X-ray scattering (SAXS) with the aim of demonstrating versatile roles played by polymer-ion interactions. In the isothermal quiescent crystallization process, a decrease in the crystal growth rate is observed for PEO-NaI and is attributed to slow chain movement caused by the coordination between cations and polymer. In situ SAXS on extensional flow-induced crystallization (FIC) exhibits enhanced kinetics and orientation for both PEO and PEO-NaI with increasing strain rate. However, an overall weaker strain-rate dependence of FIC is observed for PEO-NaI, which can be interpreted as a synergistic consequence of promoted nucleation under flow and impeded crystal growth by polymer-ion interaction. A possible microscopic mechanism is proposed to account for the experimental observation based on the formation of transient cross-linking points in PEO-NaI and their influence on the entanglement network of polymer under various flow fields. The disclosed strain-rate dependence and various ion effects on the behavior of PEO-salt composites contribute to a comprehensive understanding of polymer-ion solid polyelectrolytes. [ABSTRACT FROM AUTHOR]

Double network structure constructedwith filler network of carbonblack and molecular network of natural rubber possesses excellenttoughness and strength. However, due to lack of proper insituimaging techniques to detect the structural evolutionsunder loading, the reinforcement mechanism of filler network is stillunder debate. Here in situsynchrotron radiationX-ray nano-computed tomography with high spatial resolution (100 nm)is employed to study structural evolution of carbon black in a largevolume of natural rubber matrix. For the first time, strain-induceddeformation, destruction, and reconstruction of filler network aredirectly observed under cyclic loading. Combining mechanical test,the reinforcing and toughening effect of filler network is quantitativelyassigned to three mechanisms, namely elastic deformation, destruction,and friction of filler network. Elastic deformation mainly occursat low strain for energy storage, while network destruction playsthe dominant role at larger strain to dissipate strain energy. Additionally,friction is another energy dissipation mainly at low strain. [ABSTRACT FROM AUTHOR]

In practical processing, polymer melts generally experience flow and pressure fields simultaneously, but their flow-induced crystallization behavior under pressure was barely investigated. For this reason, we provided an insight into the crystallization behavior and crystalline morphology and structure of isotactic polypropylene (iPP) obtained under the combination of flow (2.5-22.5 s-1) and high pressure (200 MPa) by using self-designed pressurizing and shearing device. Unprecedented iPP spherulites were observed, which are composed of oriented thick lamellae (18 nm) with ultrahigh melting temperature (179.5 °C). Such spherulitic crystals with lamellae aligning perpendicular to flow have never been reported. All samples have a double melting peak behavior including an additional low temperature peak (165-169 °C) apart from the ultrahigh melting peak. The in situ synchrotron X-ray measurements show that the parents of cross-hatched structure are responsible for the ultrahigh melting temperature and the daughters give rise to the low temperature melting peak because the parents crystallized much earlier and had a higher growth rate than the daughters. Moreover, the parents are all in α-form while the daughters consist of α- and γ-forms. Our results afford a new method to obtain thick lamellae in a relatively short time. [ABSTRACT FROM AUTHOR]

On the basis of the duality of theshish-kebab superstructure,coil–stretch transition (CST) is well recognized as the molecularmechanism for shish-kebab formation in polymer melts, which, however,is challenged by recent results in flow-induced crystallization (FIC).In this work, we perform a real time investigation on FIC of polyethylenebimodal blends by combing a unique homemade extensional rheometerand synchrotron radiation small-angle X-ray scattering. The resultsshow that the critical strain for shish formation decreases with increasinglong chain concentration, which contradicts the role of CST but agreeswell with stretched network model (SNM). Quantitative analyses indicatethat the formation of shish is determined by the degree of networkdeformation rather than solely by strain or long chain concentrationat a specific temperature. In addition, three types of shish withdifferent stability are observed sequentially by increasing strain.On the basis of our results, strong support is given to the idea thatshish formation is a kinetic process. When stretched to a criticaldeformation degree, the aligned segments couple with each other toform fibrillar-like type I shish, which further transform into typeII shish embedded with sporadic lamellae and type III shish embeddedwith well-defined periodic lamellae sequentially by increasing flowintensity. Our results and the resulting conceptual model not onlydemonstrates that shish formation is derived from SNM but unveilsits kinetic process from initial chain configuration to final stablenuclei. [ABSTRACT FROM AUTHOR]

As an indispensible material for modern society, natural rubber possesses peerless mechanical properties such as strength and toughness over its artificial analogues, which remains a mystery. Intensive experimental and theoretical investigations have revealed the self-enhancement of natural rubber due to strain-induced crystallization. However a rigorous model on the self-enhancement, elucidating natural rubber's extraordinary mechanical properties, is obscured by deficient understanding of the local hierarchical structure under strain. With spatially resolved synchrotron radiation micro-beam scanning X-ray diffraction we discover weak oscillation in distributions of strain-induced crystallinity around crack tip for stretched natural rubber film, demonstrating a soft-hard double network structure. The fracture energy enhancement factor obtained by utilizing the double network model indicates an enhancement of toughness by 3 orders. It's proposed that upon stretching spontaneously developed double network structures integrating hierarchy at multi length-scale in natural rubber play an essential role in its remarkable mechanical performance. [ABSTRACT FROM AUTHOR]

A small-angle x-ray scattering (SAXS) system with a vertical layout (V-SAXS) has been designed and constructed for in situ detection on nanostructures, which is well suitable for in situ study on self-assembly of nanoparticles at liquid interface and polymer processing. A steel-tower frame on a reinforced basement is built as the supporting skeleton for scattering beam path and detector platform, ensuring the system a high working stability and a high operating accuracy. A micro-focus x-ray source combining parabolic three-dimensional multi-layer mirror and scatteringless collimation system provides a highly parallel beam, which allows us to detect the very small angle range. With a sample-to-detector distance of 7 m, the largest measurable length scale is 420 nm in real space. With a large sample zone, it is possible to install different experimental setups such as film stretching machine, which makes the system perfect to follow the microstructures evolution of materials during processing. The capability of the V-SAXS on in situ study is tested with a drying experiment of a free latex droplet, which confirms our initial design. [ABSTRACT FROM AUTHOR]

In this paper, ZnO/Ag core-shell hybrid nanocomposites have been prepared by a very simple chemical methodology. ZnO nanorods were employed as core material for Ag seeds, and subsequent nucleation and growth of Ag nanoparticle by a cationic surfactant cetyltrimethylammonium bromide (CTAB) formed the ZnO NRs/Ag core-shell nanocomposites. In addition, their morphology, microstructure and optical properties have been characterized by X-ray diffraction, Raman Spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, UV-Vis absorption and photoluminescence spectroscopy. It was found that face-center-cubic Ag nanoparticles with an average diameter of 20nm were coated onto the surface of hexagonal phase ZnO nanorods with a minimum of 0.09mmol concentration of CTAB. The excitonic absorption band and surface plasmon absorption band of the ZnO NRs/Ag nanocomposites revealed red-shifts relative to pure ZnO nanorods and metallic Ag nanoparticles. The coating of Ag nanoparticles onto the ZnO nanorods show red-shift in the near band edge (NBE) luminescence spectra and a reasonable detraction in the deep level emission (DLE) spectra compared with the pure ZnO nanorods. These interpretations demonstrated the strong interfacial interaction between Ag nanoparticles and ZnO nanorods. Furthermore, the annealing of ZnO NRs/Ag nanocomposite at 200°C was done and improvement occurs in the crystallinity and binding strength of Ag nanoparticles. [ABSTRACT FROM AUTHOR]

Poly(2,5-dimercapto-1,3,4-thiadiazole) (PDMcT)/sulfonated graphene conductive composite (PDMcT/SGS) was synthesized through in situ oxidative polymerization in the presence of the water-soluble sulfonated graphene sheets (SGS). Raman spectra revealed the existence of the π-π interaction between thiadiazole rings and basal planes of SGS. Scanning electron microscopy and transmission electron microscopy showed that the submicron-sized petals and nanofibers of PDMcT grew onto the surface of SGS. As evidenced by the cyclic voltammetry results, the incorporation of SGS has significantly improved the electrochemical activity and cyclability of PDMcT. The discharge capacity of PDMcT/SGS composite, measured with the charge-discharge tests, was 268 mAh g at the first cycle and 124 mAh g after 10 cycles. [ABSTRACT FROM AUTHOR]

The conformational ordering in spherulites of isotactic polypropylene during growing process is studied with in situ infrared microspectroscopic imaging. A comparison between the intensity distribution of bands representing crystal and conformational ordering indicates that large concentration of conformational ordered segments exist in the growth boundary region of spherulites, which suggests that conformational ordering takes place before packing into crystal lattice in the growth boundary layer. The width of the growth boundary layer is sensitive to temperature but keeps relative constant during isothermal crystallization process. Though the interchain organization of the conformational ordered segments is not clear yet, conformational ordering in the growth boundary layer is assigned to be a preordering step of crystallization. [ABSTRACT FROM AUTHOR]

A combination of extensional rheological and in situ synchrotron radiation small-angle X-ray scattering (SR-SAXS) measurements was introduced to investigate critical strain ε* for shish formation and validate whether coil−stretch transition or stretched-network is responsible for shish-kebab formation in high density polyethylene melt. With strain rates ε̇ larger than a specific value, the critical strain ε* required to induce shish formation turns out to be a constant of about 1.57, which ensure full extension of chain segments with critical entanglement molecular weight locked between two adjacent entanglement points. The results clearly demonstrate that the formation of shish-kebab in polymer melt stems from stretched network instead of coil−stretch transition. [ABSTRACT FROM AUTHOR]

Flow-induced conformational ordering in the supercooled isotactic polypropylene (iPP) is studied with in situ Fourier transform infrared spectroscopy (FTIR) coupled to an extrusion slit die. At temperature around the normal melting point of iPP, helices with monomer numbers up to 12 and 14 can be induced by shear. A window of shear strength exists to induce helices with different lengths, which increases with temperature. After the cessation of shear, the intensity of the 841 cm−1band in FTIR spectra, corresponding to helices with 12 monomers, increases sharply in the first stage, which is followed by a slow growth process, whereas a reduction of shorter helices is observed after the cessation of shear. The different trends of intensity evolutions of the long and short helical bands suggest that a coupling between coil−helix transition and intermolecular ordering occurs with helices with a length of 12 monomers, which eventually leads to an isotropic−liquid-crystal transition. Therefore, the flow-induced precursor may be a liquid crystal phase, which will transform into crystal and initiate crystal growth later. [ABSTRACT FROM AUTHOR]

Whether a phase separation or a cocrystallization occurs in poly(hexamethylene succinate-co-hexamethylene adipate) (P(HS-co-HA)) copolymers was studied with a combination of wide-angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR) spectroscopy. With HA as the majority, the presence of HS comonomers leads to weakening and broadening of (10l) peaks in the X-ray fiber diffraction patterns, while a crystal structure similar to PHS is formed in the copolymer with HS as the majority. The X-ray diffraction patterns imply possible cocrystallization between HS and HA comonomers, but cannot lead to an unambiguous conclusion, which was clarified with the compensative tool of FTIR. Following the characteristic absorption bands of crystals, cocrystallization of HS and HA comonomers was observed in copolymers with HA comonomer as the majority during which HA initiated the nucleation at high temperatures. With HA as minority, cocrystallization of HS and HA can still be achieved with a fast quenching to below 0 °C, while a phase separation occurs and only HS comonomer crystallizes at high temperatures. This demonstrates that P(HS-co-HA) has an asymmetric phase diagram. Because of the sensitivity to local conformations, FTIR spectroscopic method is demonstrated to be a powerful tool on study phase behaviors of polymers with similar crystal structure. [ABSTRACT FROM AUTHOR]

The shear-induced coil−helix transition of isotactic polypropylene (iPP) has been studied with time-resolved Fourier transform infrared spectroscopy at various temperatures. The effects of temperature, shear rate, and strain on the coil−helix transition were studied systematically. The induced conformational order increases with the shear rate and strain. A threshold of shear strain is required to induce conformational ordering. High temperature reduces the effect of shear on the conformational order, though a simple correlation was not found. Following the shear-induced conformational ordering, relaxation of helices occurs, which follows the first-order exponential decay at temperatures well above the normal melting point of iPP. The relaxation time versus temperature is fitted with an Arrhenius law, which generates an activation energy of 135 kJ/mol for the helix−coil transition of iPP. At temperatures around the normal melting point, two exponential decays are needed to fit well on the relaxation kinetic of helices. This suggests that two different states of helices are induced by shear: (i) isolated single helices far away from each other without interactions, which have a fast relaxation kinetic; (ii) aggregations of helices or helical bundles with strong interactions among each other, which have a much slower relaxation process. The helical bundles are assumed to be the precursors of nuclei for crystallization. The different helix concentrations and distributions are the origin of the three different processes of crystallization after shear. The correlation between the shear-induced conformational order and crystallization is discussed. [ABSTRACT FROM AUTHOR]

Magnetic Fe 3O 4hollow spheres were successfully synthesized with a water in oil in water (W/O/W) emulsion. During the facile procedure, no high pressure, high temperature, or other complex reaction conditions were required. Transmission electric microscope (TEM) images showed that all the hollow structural products have a good spherical morphology with an average diameter of 160 nm. The average size and the size distribution were further determined with dynamic light scattering (DLS), which reveals that the hollow nanospheres have a narrow size distribution. The average size from DLS was about 180 nm, which approximated that from TEM data. X-ray diffraction (XRD) demonstrates that the products were all Fe 3O 4phase without any impurity. By increasing or decreasing the dosage of precipitate and precipitant sources, we controlled the shell thickness successfully in the tens of nanometers range. The formation mechanism of those hollow magnetic nanospheres was discussed by using the “reverse micelle transport” mechanism. [ABSTRACT FROM AUTHOR]

The crystal structures of poly(hexamethylene sebacate- co-hexamethylene adipate), P(HSe- co-HA), copolymers have been studied with Fourier transformation infrared spectroscopy (FTIR) and X-ray fiber diffraction. All characteristic FTIR absorption bands of the crystals of HSe and HA comonomers are present in all copolymers, and each copolymer has only one melt temperature, which supports that P(HSe- co-HA) copolymers cocrystallize in a whole range of comonomer compositions. In addition to peak shift, some new diffraction peaks were observed in X-ray fiber diffraction patterns of the copolymers, which correspond to new crystals with different unit cells from those of the homopolymers. The crystal structures of the copolymers were analyzed, which varied with the composition of HA and HSe comonomers. Interestingly, the lattice constants cof P(HSe- co-20 mol % HA) and P(HSe- co-35 mol % HA) crystals are even larger than those of either homopolymers, which implies a new length scale may be induced in the random copolymers. This supports the formation of new crystals instead of normal lattice distortion. [ABSTRACT FROM AUTHOR]

Deformation-induced crystallization of living polymer sulfur was studied with in situ wide-angle X-ray scattering, where chain scission plays a critical role. The onset of crystallization always occurs at the minimum stress point after the yield point, though different drawing rates were applied. With large drawing rates, deformation effect dictates the chain scission and linear chain−ring transition, which leads to the formation of linear chain fibrous phase, while only cyclooctasulfur crystals form at small drawing rates where the thermal effect is mainly responsible for the chain−ring transition. The scission of linear chains not only generates the building units for crystallization but also releases chains from entanglement and consequently enhances their mobility and crystallization rate. A critical point is found at an intermediate drawing rate where no crystallization occurs before the complete breakage of the samples. With the large or small drawing rates, the crystallization rate is faster than rates of chain scission induced by deformation or the thermal effect; crystallization occurs before sample breaking, where fibrous phase and cyclosulfur crystals act as cross-link and filler, respectively. With the critical drawing rate, the nucleation rate of crystals is slower than that of chain scission, and the sample breaks before the onset of crystallization. [ABSTRACT FROM AUTHOR]

Previous research on the binding and gelation of calcium/alginate in aqueous solution were mostly conducted in the (semi-)concentrated regime, and it did not provide details of the binding process and the formation of egg-box junctions. In the present investigation, the binding of calcium to alginate, of low and high molecular weight and different guluronate/mannuronate ratios, was investigated in dilute solutions using isothermal titration calorimetry (ITC), Ca2-selective potentiometry, and viscometry techniques. The results reveal three distinct and successive steps in the binding of calcium to alginate with increased concentration of Ca ions. They were assigned to (i) interaction of Ca2with a single guluronate unit forming monocomplexes; (ii) propagation and formation of egg-box dimers via pairing of these monocomplexes; and (iii) lateral association of the egg-box dimers, generating multimers. The third step has different association modes depending on the molecular weight of alginate. The boundaries between these steps are reasonably critical, and they closely correlate with the Ca/guluronate stoichiometry expected for egg-box dimers and multimers with 2/1 helical chains. The formation of egg-box dimers and their subsequent association are thermodynamically equivalent processes and can be fitted by a model of independent binding sites. The binding of Ca to alginates of different guluronate contents is controlled by a balance between enthalpy and entropy. [ABSTRACT FROM AUTHOR]

In this work, we have carried out 2 dimensional small and wide angle X-ray scattering experiments on the blends of linear low-density polyethylene (LLDPE) and isotactic polypropylene (iPP) obtained by dynamic packing injection molding in which the melt was firstly injected into the mold then forced to move repeatedly in a chamber by two pistons that moved reversibly with the same frequency as the solidification progressively occurred from the mold wall to the molding core part. iPP was found to form a shish-kebab structure with its lamellar stack oriented perpendicularly to the shear flow direction. Very interestingly, the lamellae of LLDPE were found tilted away from shear flow direction with molecular chain still along flow direction, and the tilted angle increases from the skin to the core part. This can be only understood if the intra-lamellar block slip in the chain direction is generally activated during shearing process achieved by dynamic packing injection molding. Our finding is important and seems to provide further support for the idea that the structure of the crystalline lamellae is not continuous but constructed of small building units with thin boundary in between. [ABSTRACT FROM AUTHOR]

Background and Aims: The failure to reduce the mortality of patients with solid tumours is mainly a result of the early dissemination of cancer cells to secondary site, which is usually missed by conventional diagnostic procedures used for tumour staging. The possibility to use easily accessible body fluids as a source for circulating tumour cells (CTCs) detection enables longitudinal observations of the disease. In the study, we evaluated the CTCs in lung cancer following locoregional radiation therapy. Methods: Samples of 5ml peripheral blood was taken from each lung cancer patients (n=15) both before and after the radiotherapy course. Meanwhile tumour size was determined by chest X-ray or computed tomography. Using cytokeratin 19(CK19) as marker,the blood samples were subjected to real time RT-PCR assay. All patients with lung cancer were treated with primary definitive and mediastinal radiotherapy. Results Compare to that of pre-treatment, the value of CK19 mRNA in peripheral blood after therapy decreased dramatically(5.0932±1.0628 vs. 4.2493±0.8323,t=3.192,P=0.007). The change of CK19 mRNA level before and after radiotherapy was closely related to the type (NSCLC vs. SCLC, 0.5389±0.9030 vs. 1.6826±0.9467,t=2.1465,P=0.051). Meanwhile, there appeared to be a close link between the grade (Well/Mod vs. Poor) and the change of CK19 mRNA (0.5024 vs. 1.5271,t=2.017,P=0.065). The change of CK19 mRNA level was related to variation of tumour burden during radiotherapy(r=0.0575,P=0.025). Of the 15 cases studied, 12 cases were positive before radiotherapy (12/15,80%). The positive rate was 53%(8/15) after radiotherapy, meaning that four patients converted into negative after radiotherapy. Conclusions: The disseminated circulating cancer cells can be affected by radiotherapy; meanwhile further more systemic adjuvant treatment should be conducted. Due to concordance between molecular response and radiological remission, assessment of the therapeutic response might be possible by serial quantitative of CTCs. [ABSTRACT FROM AUTHOR]

The designed aromatic amide discotic molecule with sulfonic acid groups at its periphery exhibits a hexagonal supramolecular columnar liquid crystalline phase, which leads to the achievement of anisotropic ionic conductivity through macroscopically aligning the ionic channels. [ABSTRACT FROM AUTHOR]

The designed aromatic amide discotic molecule with sulfonic acid groups at its periphery exhibits a hexagonal supramolecular columnar liquid crystalline phase, which leads to the achievement of anisotropic ionic conductivity through macroscopically aligning the ionic channels. [ABSTRACT FROM AUTHOR]