Changes in the microphase-separated structure of the poly­(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) triblock copolymer (13 wt % polystyrene (PS) block) were investigated during mechanical deformation. In situ synchrotron radiation small-angle X-ray scattering (SAXS)/wide-angle X-ray scattering (WAXS) measurements were successfully performed for SEBS under equi-biaxial deformation as well as under uniaxial deformation. In situ SAXS/WAXS measurements revealed changes in (1) the shape of spherical PS domains, (2) the spacing of PS domains packed in the body-centered cubic structure in the initial state, (3) their ordering, and (4) the orientation of PEB chains during deformations. In terms of the microdomain structure, affine deformation was kept below a certain strain (εd‑A), which are 4 and 1.2 for uniaxial and equi-biaxial deformation, respectively. In contrast, the ordering of the arranged PS domains decreased from the initial strain region. Above the εd‑A value, deviation from affine deformation started to occur. This deviation is related to contact of PS domains under mechanical deformation. Uniaxial stretching still showed the plane-independent behavior, while equi-biaxial stretching did not. Moreover, the εd‑A value for equi-biaxial deformation was smaller than that for uniaxial deformation and further smaller than expected. This might be because the entanglement effect was enhanced for equi-biaxial deformation. Furthermore, after contact of PS domains at around strains of 6 and 2, during uniaxial and equi-biaxial deformation, respectively, the ordering of PS domains suddenly increased with an increase in strain. It is inferred that the locked state between the PS domains and the extended PEB chains formed during deformation may have been released and repacked at a certain strain.

The strength of silica-based mechanochromic nanocomposites was improved by a novel nanocomposite synthesized by grafting poly(butyl acrylate) (PBA)-b-poly(methyl methacrylate) (PMMA) from silica nanoparticles (SiNP). Samples with different PMMA/PBA ratios were prepared to clarify the effect of the rubbery/glassy block copolymer ratios on the mechanical properties of the nanocomposites. The nanocomposites formed a face-centered cubic paracrystal-like structure and exhibited structural color. Timeresolved ultrasmall-angle X-ray scattering was carried out to investigate the structural evolution of the nanocomposites by uniaxial and biaxial mechanical deformation. Changes in color and mechanochromic properties were observed at varying distances between the particles by mechanical deformation. The nanocomposites exhibited elastic and plastic properties and became more rubber-like as the rubbery PBA weight ratio increased. The polymer brush deformed into a prolate spheroid by uniaxial stretching, and the distance between SiNP decreased in the direction perpendicular to elongation, which resulted in the color change by mechanical deformation. Moreover, the distance between SiNP increased isotropically by biaxial stretching. The polymer brush was elongated isotropically toward the in-plane direction and deformed into an oblate spheroid.

The deformation behavior of polythiourethane (PTU) elastomers was investigated using in situ small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), and X-ray absorption fine structure (XAFS) methods. Two PTUs were prepared from poly­(oxytetramethylene) glycol, 1,4-bis­(isocyanatomethyl) cyclohexane, and 1,4-butanedithiol (PTU-B) or 1,5-pentanedithiol (PTU-P). The effect of methylene length of the chain extender on molecular aggregation structure of PTU during the elongation process was evaluated. SAXS measurement revealed that the spacing of hard segment domains of PTUs increased and decreased in the directions parallel and perpendicular to the elongation direction and showed a constant value of strain above 2. The strain calculated from the spacing of the hard segment domains for PTU-B was larger than that for PTU-P, suggesting that well-developed hard segment domains were formed for PTU-B. WAXD measurement showed that strain-induced crystallization of the soft segment occurred at around the strain of 2. XAFS measurement showed that at the strain of 2 or 3, atoms in the vicinity of sulfur became more ordered, which is confirmed by the decrement of the extended XAFS Debye–Waller factor. It seems reasonable from these SAXS, WAXD, and XAFS results that the hard segment domains orientation occurred for both PTUs during the deformation process, followed by strain-induced crystallization of the soft segment. In addition, PTU-B exhibits more ordered hard segment domains that maintain their aggregation structure upon uniaxial deformation in comparison with PTU-P.

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SummaryWe first describe early uses of the centrifuge for deciphering physical properties and molecular organization within living cells, as well as the development and use of centrifuge microscopes for such studies. The rationale for developing a centrifuge microscope that allows high-extinction polarized light microscopy to observe dynamic fine structures in living cells is next discussed. We then describe a centrifuge polarizing microscope (CPM) that we developed for observing fine structural changes in living cells which are being exposed to up to < 11 500 times earth's gravitational field (g).With the specimen housed in a rotor supported on an air spindle motor, and imaged through an external microscope illuminated by a precisely synchronized flash of less than 10 ns duration from a Nd:YAG laser, the image of the spinning object remains steady up to the maximum speed of 11 700 rev min 21 , or up to < 11 500  g. The image is captured, at up to 25 frames s 21 , by an interference-fringefree CCD camera that is synchronized to the centrifuge rotor. At all speeds (in 100 rev min 21 increments), the image is resolved to better than 1 mm, while birefringence of the specimen, housed in a specially designed specimen chamber that suffers low-stress birefringence and prevents leakage of the physiological solutions, is detected with a retardance sensitivity of better than 1 nm. Differential interference contrast and fluorescence images (532 nm excitation) of the spinning specimen can also be generated with the CPM.The second part of this study (Inoue  et al., J. Microsc. 201 (2001) 357±367, describes several biological applications of the CPM that we have explored. Individual live cells, such as oocytes and blood cells, are supported on a sucrose or Percoll density gradient while other cells, such as cultured fibroblasts and Dictyostelium amoebae, are observed crawling on glass surfaces. Observations of these cells exposed to the high G fields (centripetal acceleration/g) in the CPM are yielding many new results that lead to intriguing questions regarding the organization and function of fine structures in living cells and related quasi-fluid systems.