Observation of Water-Stimulated Supercontraction of Uniaxially Oriented Poly(vinyl alcohol) and the Related Hierarchical Structure Change Revealed by the Time-Resolved WAXD/SAXS Measurements

A uniaxially oriented poly­(vinyl alcohol) (PVA) film was found for the first time to respond to the humidity change in the two different modes under the restrained condition, which are essentially the same as the modes of the supercontraction and cyclic contraction observed in spider dragline silk. Once the atmospheric humidity started to increase, the PVA film showed at first the irreversible stress generation (supercontraction stress), followed by the reversible stress generation synchronizing with the cyclic change of humidity. These irreversible and reversible stress changes have been connected to the changes of higher-order structure caused by the cyclic change of wet/dry atmosphere as revealed by the detailed <i>in situ</i> measurements of the 2-dimensional wide-angle and small-angle X-ray scatterings during these processes. On the basis of a simple mechanical model and the thus-collected information on the higher-order structural change, it was concluded that the irreversible and reversible stress generations are governed mainly by the irreversible hydration-induced stress relaxation in the highly tensioned amorphous region and the reversible swelling in the normal amorphous region, respectively

Fully Liquid-Crystalline ABA Triblock Copolymer of Fluorinated Side-Chain Liquid-Crystalline A Block and Main-Chain Liquid-Crystalline B Block: Higher Order Structure in Bulk and Thin Film States

Fully liquid-crystalline (LC) ABA-type triblock copolymers were synthesized by atom transfer radical polymerization; the A block was a fluorinated side-chain LC polymer, PFA-C₈, and the B block was a main-chain LC polyester, BB-5­(3-Me). The volume fraction of the A block (φ_A) was 0.11–0.70, and the B block had a constant molecular weight. Nanometer-scale segregated structures in the bulk and thin film states were investigated by synchrotron X-ray diffraction (XRD) in transmission and grazing-incidence (GI) geometries to examine the effect of competition between the LC orientation and polymer chain dimensions on the morphology. When φ_A is 0.11, matching of the mesogen orientation in the A and B blocks dominates the main-chain orientation, whereas when φ_A exceeds 0.28, matching of the lateral dimensions of the A and B blocks dominates the mesogen orientation, although all the polymers showed lamellar structure before isotropization of BB-5­(3-Me). GI-XRD revealed that the lamellar structure in the thin film with φ_A = 0.70 was completely perpendicular to the Si substrate without surface modification or solvent annealing

Transformation of Coiled α‑Helices into <i>Cross</i>-β-Sheets Superstructure

The fibrous silk produced by bees, wasps, ants, or hornets is known to form a four-strand α-helical coiled coil superstructure. We have succeeded in showing the formation of this coiled coil structure not only in natural fibers, but also in artificial films made of regenerated silk of the hornet <i>Vespa simillima xanthoptera</i> using wide- and small-angle X-ray scatterings and polarized Fourier transform infrared spectroscopy. On the basis of time-resolved simultaneous synchrotron X-ray scattering observations for in situ monitoring of the structural changes in regenerated silk material during tensile deformation, we have shown that the application of tensile force under appropriate conditions induces a transition from the coiled α-helices to a <i>cross</i>-β-sheet superstructure. The four-stranded tertiary superstructure remains unchanged during this process. It has also been shown that the amorphous protein chains in the regenerated silk material are transformed into conventional β-sheet arrangements with varying orientation

Design of High-Density Helical Polymer Brush on Silica Nanoparticles for the Size Recognition of Fullerene Molecules

High-density syndiotactic poly­(methyl methacrylate) (<i>st-</i>PMMA) brushes form a helical structure and encapsulate fullerene molecules in their helical cavities, leading to a PMMA brush/fullerene inclusion complex. The brushes recognize the size of guest molecules and spontaneously adapt their helical diameter to the guest molecules. Both polymer brush/C₆₀ and polymer brush/C₇₀ inclusion complex on the flat substrate were characterized on the basis of grazing incidence wide-angle X-ray diffraction (GIWAXD) measurements, and it is revealed that the main chains oriented perpendicular to the substrate. Moreover, high-density <i>st</i>-PMMA brushes grafted onto nanoparticles efficiently separate C₇₀ molecules from the mixture of C₆₀ and C₇₀ solution. Even after 5× repeating process, the selectivity for C₇₀ molecules remains at 99%

Confinement-Induced Crystal Growth in One-Dimensional Isotactic Polystyrene Nanorod Arrays

This work demonstrates the anomalous crystal growth of isotactic polystyrene (iPS) in nanorod arrays with different rod sizes. At the bottom of the nanorods, the crystals in bulk film grow into nanorods along either the [110] or [100] direction parallel to the rod axis. On the top side of the nanorods, the polymer exhibits different orientations corresponding to weak or strong confinement. In the weaker confinement (bigger nanorods of 300 nm diameter), the crystals grow with the [100] direction along the nanorod, which is similar to the crystals developed in the radial of spherulite. In the stronger confinement (smaller nanorods of 65 nm diameter), the splaying of crystals in the rod is significantly suppressed, and the preferred growth direction of iPS crystals is kept in either the [110] or [100] direction. The precise control of polymer crystal orientation and crystallinity at a local scale opens important perspectives for the design of one-dimensional nanomaterials whose performance depends on the anisotropic crystal properties

Salt Dependence of the Chain Stiffness and Excluded-Volume Strength for the Polymethacrylate-Type Sulfopropylbetaine in Aqueous NaCl Solutions

A series of zwitterionic polyelectrolytes poly­[3-(<i>N</i>-2-methacryl­oyloxy­ethyl-<i>N</i>,<i>N</i>-dimethyl)­ammonato­propane­sulfonate] (PMAPS) with a wide range of weight-average molecular weight (<i>M</i>_w) between 5.5 × 10³ and 1.6 × 10⁶ g mol^–1 with narrow molecular weight distribution (<i>M</i>_w/<i>M</i>_n = 1.07–1.19) were thoroughly characterized in aqueous NaCl solutions for salt concentration (<i>C</i>_s) over a range from theta <i>C</i>_s (0.074 M) to 1.0 M by synchrotron radiation small-angle X-ray scattering (SAXS), light scattering, and viscometry at 25 °C. To determine the chain stiffness parameter (λ^–1) and the excluded-volume strength (<i>B</i>) of PMAPS in an aqueous NaCl solution, SAXS profiles and the <i>M</i>_w dependences of the radius of gyration, the second virial coefficient, the interpenetration function, the hydrodynamic radius, and the intrinsic viscosity for PMAPS were analyzed on the basis of the (un)­perturbed cylindrical wormlike chain model. The experimental λ^–1 value for PMAPS chains in aqueous NaCl solutions barely decreased but was almost constant with the increasing <i>C</i>_s, whereas the value of <i>B</i> was increased gradually with the increasing <i>C</i>_s. Thus, the dominant factor for the chain dimension of PMAPS in aqueous NaCl solutions was the long-range interaction (i.e., <i>B</i>) than the short-range interaction (i.e., λ^–1). The observed <i>C</i>_s dependences of λ^–1 and <i>B</i> for PMAPS chains in aqueous NaCl solutions were fairly described by the theories of the polyampholyte with the nonrepulsive, the repulsive, and the attractive electrostatic interactions

Molecular Aggregation States and Physical Properties of Syndiotactic Polystyrene/Hydrogenated Polyisoprene Multiblock Copolymers with Crystalline Hard Domain

Molecular aggregation structure and mechanical as well as thermal properties of novel well-defined multiblock copolymers consisting of crystalline syndiotactic polystyrene (sPS) and rubbery hydrogenated polyisoprene (hPIp) were investigated. The morphology and crystalline ordered structure of the multiblock copolymer films prepared by solvent casting from 1,2-dichlorobenzene solution depended on the volume fraction of sPS (VF_sPS) and number of blocks. The multiblock copolymer films exhibited ordered morphology with low crystallinity. The crystallinity of the sPS reduced with decreasing the VF_sPS. The pentablock copolymer produced more ordered morphology and less crystallinity than the triblock copolymers. The anisotropic orientation and mechanical stability of the δ form sPS crystals in the spherical sPS domains during uniaxial stretching were demonstrated. Tensile testing and dynamic mechanical analysis indicated that these multiblock copolymer films with appropriate sPS fraction are strong, tough, and elastic and thus could be potential candidates for a new type of thermoplastic elastomer with discrete crystalline hard domains

Hierarchical Structural Change in the Stress-Induced Phase Transition of Poly(tetramethylene terephthalate) As Studied by the Simultaneous Measurement of FTIR Spectra and 2D Synchrotron Undulator WAXD/SAXS Data

The simultaneous measurement of Fourier transform infrared (FTIR) transmission spectra and 2-dimensional wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) patterns has been performed successfully to investigate the hierarchical structure changes occurring in the stress-induced phase transition phenomenon of uniaxially oriented poly­(tetramethylene terephthalate) film. The molar fraction of the β-crystal form, evaluated from the IR and WAXD data analyses, increased steeply in the plateru region of the stress–strain curve as already known well. The 2D SAXS data have revealed the remarkable and reversible change in the stacked lamellar structure just after the α-to-β phase transition was completed, where the tilting angle of the stacked lamellae measured from the draw axis of the oriented sample became zero, and the lamellar thickness increased due to the inclusion of amorphous region located in the boundary part of the crystalline lamellae. In parallel, the X-ray reflection spots in a wider diffraction angle region became diffuse in the observed WAXD pattern of the β form, indicating the packing disorder of the mechanically stressed chains. In this way, the simultaneous combination of the 3 different types of equipments has allowed us to deduce the detailed structural change from the various levels: the stress-induced α–β transition was found to occur not only with the remarkable changes in the molecular chain conformation and chain packing mode in the crystal lattice, but also with the large and reversible change in the lamellar stacking structure. The stress-induced changes in lamellar thickness and long period were simulated using a mechanical model with these hierarchical structure changes taken into account, giving relatively good reproduction of the observed data

Hydrophobic Molecules Infiltrating into the Poly(ethylene glycol) Domain of the Core/Shell Interface of a Polymeric Micelle: Evidence Obtained with Anomalous Small-Angle X‑ray Scattering

Polymeric micelles have been extensively studied as nanoscale drug carriers. Knowing the inner structure of polymeric micelles that encapsulate hydrophobic drugs is important to design effective carriers. In our study, the hydrophobic compound tetrabromocathecol (TBC) was chosen as a drug-equivalent model molecule. The bromine atoms in TBC act as probes in anomalous small-angle X-ray scattering (ASAXS) allowing for its localization in the polymeric micelles whose shape and size were determined by normal small-angle X-ray scattering (SAXS). Light scattering measurements coupled with field flow fractionation were also carried out to determine the aggregation number of micelles. A core–corona spherical model was used to explain the shape of the micelles, while the distribution of bromine atoms was explained with a hard-sphere model. Interestingly, the radius of the spherical region populated with bromine atoms was larger than the one of the sphere corresponding to the hydrophobic core of the micelle. This result suggests that the TBC molecules infiltrate the PEG hydrophilic domain in the vicinity of the core/shell interface. The results of light scattering and SAXS indicate that the PEG chains at the shell region are densely packed, and thus the PEG domain close to the interface has enough hydrophobicity to tolerate the presence of hydrophobic compounds

Depth-Resolved Characterization of Perylenediimide Side-Chain Polymer Thin Film Structure Using Grazing-Incidence Wide-Angle X‑ray Diffraction with Tender X‑rays

Polymers with a perylenediimide (PDI) side chain (PAc12PDI) consist of two kinds of crystalline structures with various types of orientations in a thin film. Understanding the population of the microcrystalline structure and its orientation along the thickness is strongly desired. Grazing-incidence wide-angle X-ray diffraction (GIWAXD) measurements with hard X-rays, which are generally chosen as λ = 0.1 nm, are a powerful tool to evaluate the molecular aggregation structure in thin films. A depth-resolved analysis for the outermost surface of the polymeric materials using conventional GIWAXD measurements, however, has limitations on depth resolution because the X-ray penetration depth dramatically increases above the critical angle. Meanwhile, tender X-rays (λ = 0.5 nm) have the potential advantage that the penetration depth gradually increases above the critical angle, leading to precise characterization for the population of crystallite distribution along the thickness. The population of the microcrystalline states in the PAc12PDI thin film was precisely characterized utilizing GIWAXD measurements using tender X-rays. The outermost surface of the PAc12PDI thin film is occupied by a monoclinic lattice with <i>a</i> = 2.38 nm, <i>b</i> = 0.74 nm, <i>c</i> = 5.98 nm, and β = 108.13°, while maintaining the <i>c-</i>axis perpendicular to the substrate surface. Additionally, the presence of solid substrate controls the formation of the crystallite with unidirectional orientation