Thermoreversible morphological transition (MT) of a poly(styrene-Wocfe-isoprene) diblock copolymer was studied by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The cylindrical and spherical microdomains of polystyrene (PS) which are embedded in the polyisoprene matrix were thermoreversibly observed at 150 and 200 °C, respectively. As far as we know, this work may be the first to show that the cylindrical and spherical morphologies can reversibly change with temperature. Using experimentally determined interaction parameters x> we compared SAXS and TEM results with the theory in the weak segregation limit presented by Leibler, which predicts the thermoreversible MT between spheres and cylinders. Consequently, (x-N)t < (x-Wmo °c < (\N), < (xA)i < (x-Wwo "c was obtained, where ixN)t, ixN)" and (xN)i denote the theoretical values of product at the microphase separation transition (MST), at the spinodal point of the MST, and at the MT between spheres and cylinders, respectively, and N is the degree of polymerization of the copolymer.

We present experimental results of a thermoreversible morphological transition between spheres and cylinders for polystyrene-block-polyisoprene diblock copolymers (SI) in dioctyl phthalate solutions. Morphologies were characterized using small-angle X-ray scattering (SAXS), and spherical and cylindrical states were found above and below the order-order transition (OOT) temperature, TOOT, respectively. TOOT increased with an increase of polymer concentration for the range covered in this study (higher than 70 wt % polymer concentration). The concentration dependence of TOOT was found to be given by the relationship of ( effrC)OOT/φprC ) A + B/TOOT, where ( effrC)OOT denotes the critical value of the product of eff and rC at the cylinder-sphere OOT, eff is the effective interaction parameter between styrene and isoprene segments in the presence of solvent, rC is the reduced degree of polymerization of an entire block copolymer, and φp is the volume fraction of the block copolymer in the solution. A and B are constants characterizing the temperature dependence of the segmental interaction parameter SI in bulk, where A ) -0.0258 and B ) 27.9 were evaluated by analyzing SAXS profiles from the disordered state. The critical values( effrC)OOT ) 38.4 for the cylinder-sphere transition and 30.5 e ( effrC)ODT e 32.3 for the order-disorder transition (ODT) were determined from our experimental result on the φp dependence of TOOT and that of TODT, respectively. These critical values were compared to the results of some theoretical studies. The SAXS measurements revealed thermoreversibility of the cylinder-sphere transition between 110 and 120°C for an 80 wt % solution.

Thermally induced morphology transition from cylindrical to lamellar microdomains wan found for a poly(styrenablock-butediene-block-s~ene) (SBS) triblock copolymer having a 0.66 weight fraction of polystyrene blocka by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Polybutadiene (PB) cylinders with hexagonal c l w packing were formed in a polystyrene (PS) matrix when the SBS wan cast from a methyl ethyl ketone solution. It wan found that the PB cylinders were transformed into lamellae on annealing at 160 OC. This is a transition from thermodynamically quasi-stable to stable morphologies. On the baais of SAXS and TEM, the transition turned out to occur via coalescence of cylinders without their translational movementa. It ia propoeed that an undulation of the interface induced by the inatabiIity of the interface might play an important role for the coalescence of the cylinders. It wan also found by TEM that the coherency of lamellar microdomains thus formed became higher with further annealing;i.e., the persistence length of the undulating lamellae became longer.

Gel formation was discovered in an aqueous mixture of enantiomeric triblock copolymers, PLLA‐PEG‐PLLA and PDLA‐PEG‐PDLA. This system is characteristic in that an interesting sol–gel transition was induced by the stereo‐complexation of the PLLA and PDLA segments of the block copolymers around 37°C. The process of gel formation was clearly monitored by the rheological change, and the responsibility of the stereo‐complex formation for the gelation was confirmed by wide‐angle X‐ray scattering. The mechanism of this gel formation is discussed in relation to its potential applications.

An organogel system consisting of trans-(1S,2S)-bis(ureidododecyl)cyclohexane (SS-BUC) and a series of primary alcohols was explored with optical polarizing microscopy (OPM), electron microscopy, circular dichroism (CD), wide-angle X-ray scattering (WAXS), and synchrotron small-angle X-ray scattering (SAXS). OPM, SAXS, and especially WAXS showed that the gel fiber of SS-BUC/methanol gels essentially consists of SS-BUC crystal itself. SAXS showed that the SS-BUC crystal in the gel takes a lamella with a domain spacing of 5.2 nm. When we left the gel at room temperature, the spacing decreased to 3.1 nm after several months. This distance change may correspond to the structural transition from a double-layer structure to an intercalated-layer structure, which was proposed by Feringa et al. (Chem.-Eur. J. 1999, 5, 937-950) as a possible arrangement of the molecular packing. When the gels in ethanol, propanol, butanol, or octanol were examined, they never showed crystalline peaks in WAXS and SAXS, indicating the amorphous nature of the gels. With increasing the alkyl chain length from ethanol to octanol, dramatic changes were observed in the CD spectrum in the 200-500-nm range. Because these CD changes are correlated to the absorbance of urea, those can be considered as the evidence that the solvents strongly relate to the spatial arrangement between the adjacent urea groups. For the amorphous gels, the cross-sectional correlation function [gammaCu] was directly obtained by the inverse Hankel transform of the SAXS data. The value of gammaCu for the gels is decreased with increasing u (distance between the two scattering bodies, see eq 5). Furthermore, it more rapidly decreases than that of the rigid cylinder model. This feature can be explained by the speculation that many solvent molecules permeate into the SS-BUC fiber. There was a clear difference between ethanol and the other gels, indicating that the solvents with a longer alkyl chain give the more permeated and diffused fiber. This permeated fiber (i.e., wet fiber) can rationalize the dramatic CD change, by presuming that the permeated solvent molecules alter the molecular stacking form.

Small-angle X-ray scattering (SAXS) from an organogel system prepared from methyl 4,6-O-benzylidene-α-d-mannopyranoside and p-xylene was carried out with a synchrotron X-ray source at SPring-8, which revealed that hexagonally packed fibrils are formed in the gel state. The spacing between the fibrils can be evaluated to be about 60 Å, and this value was almost independent of both the gelator concentration and the temperature. Furthermore, the spacing is larger than the gelator molecular size. Upon heating, this supramolecular structure completely disappeared. Time-resolved SAXS revealed that phase separation takes place initially and subsequently the hexagonal structure is formed. Wide-angle X-ray diffraction (WAXD) showed that there is no crystalline peak at all and the diffraction pattern is consistent with being amorphous. 1H NMR spectral data show that the gelator molecules still maintain thermal motion in the gel state. The present SAXS, WAXD, and NMR results contrast with those of “dry gels” in which the gel fibers consist of the crystal of the gelators. Our results suggest that the solvent molecules are incorporated into the gel fiber and the present gel can be classified as a “wet gel”.

We have investigated structural changes in a poly(vinyl alcohol) (PVA) film during uniaxial stretching in water by conducting simultaneously the tensile stress−strain measurement with small-angle X-ray scattering (SAXS) using our newly developed drawing apparatus for the in situ SAXS measurements. Below the strain of 70%, the crystalline lamellae orient to the direction perpendicular to the stretching direction and the intervening amorphous regions are elastically expanded with the film drawing in proportion to the macroscopic deformation. Beyond the strain of 70%, the molecular chains in the intermediate amorphous region are relaxed with the lamellar breakup. Above 180% strain, the structural transition of the lamellar structure to the microfibrillar one takes place, as suggested by appearance of the transversal streak with an intensity maximum on each streak and the mechanical transition. Moreover, interfibrillar interaction of the adjacent microfibrils decreases with the film stretching by the pulling-out of the tie chains, which are interpenetrating to the adjacent microfibrils, leading to the macroscopic plastic deformation of the PVA film and stress relaxation of most of the microfibrils, which is shown by the continuous longitudinal long period decrease. In the final stage of deformation, the networking with a long-range connectivity composed of the microfibrils and the interfibrillar extended amorphous chains proceeds associated with the sliding between the adjacent microfibrils with successive drawing. However, the network of the interfibrillar extended amorphous region is considered to be an origin of the strain-induced hardening, which occurs above 180% strain up to a break, because most of the microfibrils are relaxed with strain.

We report the morphology and phase behaviors of binary blends of polystyrene-block-polyisoprene (SI) copolymers, which were studied by a small-angle X-ray scattering (SAXS) technique. The neat SI copolymers employed in this study have almost the same molecular weights but different volume fractions of polystyrene block (φPS = 0.26 and 0.65). Blends with various overall volume fractions of polystyrene block ( ), ranging from 0.41 to 0.60, were prepared from these two SI copolymers. It was found that the morphology can be controlled by adjusting . For the blends with 0.57 ≤ ≤ 0.60, the morphological transition from lamellae to gyroid phases was observed upon increasing the temperature. We present an experimentally determined phase diagram for the blend by plotting χZ vs , where χ is the interaction parameter and Z is the reduced value of the total degree of polymerization of the block copolymer.