Search

We studied the formation and relaxation of precursors of shish-kebab in isotactic polystyrene after applying pulse shear flow at temperatures above the nominal melting temperatures Tm (=223 °C). It was found that the string-like objects that were assigned to precursors in a previous article appeared in micrometer scale up to ∼285 °C, which was very close to the equilibrium melting temperature T [ABSTRACT FROM AUTHOR]

This paper reviews the authors' investigation into polymer crystallization, especially involving a spinodal decomposition (SD) type phase separation due to the orientation fluctuation of stiff segments prior to crystal nucleation. Evidences for SD obtained from small-angle X-ray and neutron scattering (SAXS and SANS), depolarized light scattering (DPLS), Fourier-transform infrared spectroscopy (FT-IR) are discussed in detail in the case of the glass crystallization of poly(ethylene terephthalate) (PET) just above Tg. SD-like optical micrographs are also shown as a function of crystallization temperature for the melt crystallization of PET; their characteristic wavelengths Λ, which are of the order of μm above 120 °C, follow a van Aartsen equation derived from the Cahn–Hilliard theory for SD. By fitting the equation to the observed characteristic wavelengths the spinodal temperature Ts was determined to be Ts = 213 ± 5 °Cfor the PET melt, above which the SD pattern suddenly changed to the usual spherulite pattern. On the basis of a theory by Olmsted et al. [4], the general mechanisms of polymer crystallization are also discussed; the crystallization from the metastable melt causes the nucleation and growth (N & G) of dense (nematic) domains while that from the unstable melt causes SD into the dense (nematic) and less dense (isotropic) domains. Furthermore, the secondary phase separation of the SD-type phase separation into smectic and amorphous domains subsequently occurs inside the nematic domain for both these cases. [ABSTRACT FROM AUTHOR]

Perfluorosulfonic acid (PFSA) polymers are used as electrolyte membranes in polymer electrolyte fuel cells. To investigate the effect on proton conductivity through structural orientation control, we added 1,2,4-triazole to PFSA films during casting to impart anisotropy to the ion-cluster structure of the films. The proton conductivities of the films were found to be high in the film-surface direction and low in the film-thickness direction. Structural analysis using small-angle X-ray scattering suggested that the anisotropy in proton conductivity was due to anisotropy in the ion-cluster structure, which in turn was attributed to the formation of a phase-separated structure via strong bonding between sulfonic acid groups and 1,2,4-triazole during cast film formation and the surface segregation of fluorine. We expect the findings of this study to aid in the fabrication of PFSA films with controlled ion clusters. [ABSTRACT FROM AUTHOR]

Aliphatic polyurea (PUA) is a promising bioengineering plastic that can be prepared from natural resources: castor oil and carbon dioxide. Thus, PUA production could be used to sequester carbon dioxide while producing an environmentally friendly plastic. However, the crystallization behavior of PUA remains unknown. Herein, we reported the detailed analyses of crystallization behavior of PUA. Initially, upon rapid quenching from the melt, the growth of the δ-form crystallizes. Further, 100-nm scaled density fluctuations and the crystal growth process were observed during annealing. The density fluctuations can be assigned to a nodule-type structure. Three melting points after crystallization from the melt were observed by flash differential scanning calorimetry measurements. These three melting peaks were assigned to the melting of PUA nodules, temperature-dependent crystal thickening, and melting of recrystallization crystals from the nodule-type structure. Image 1 • Aliphatic polyurea (PUA) is a promising bioengineering plastic. • Crystallization of PUA on rapid cooling reported: PUA crystallizes in the δ-form. • On subsequent crystallization above 120 °C, lamellae form. • On crystallization below 120 °C, nodule-type structures form. • Distinct melting temperatures of nodules, lamellae, and recrystallized regions. [ABSTRACT FROM AUTHOR]

The novel hydrophobic surface modification of hydrogel structure, referred to as organohydrogel, was firstly achieved through the utilization of poly(N -vinylamide)s hydrogels, taking advantage of the property of polycation precursor. Following the shrinkage of poly(N -acetamide- co - N -vinylformamide), only the surface moiety was subjected to hydrolysis. Subsequently, a radical initiator was chemically tethered to the amino groups on the hydrogel surface to facilitate atom transfer radical polymerization (ATRP) of hydrophobic monomer, phenylethylacrylate. Hydrophobic layer characteristics were differentiated by varying hydrolysis time (x t) and ATRP time (y t), resulting in the creation of hydrophobic surface-modified gel (HSMgel). All HSMgels resulted in stable swelling ratio (S.R.) regardless of y t. The contact angle of water droplets increased gradually with both increasing x t and y t , from 17.6° to 91.9°, while maintaining a relatively constant S.R. The drying process of hydrophobic surface-modified HSMgels was accelerated, while that of precursor hydrophilic gels was delayed. These unique properties stemmed from the chemical structure of poly(N -vinylamide)s, which led to the formation of a chemically bound hydrophobic layer within the hydrogels. [Display omitted] • Surface modification of poly (N -vinylamide) hydrogels. • Hydrophobic modification on hydrogel. • ATRP approach enable to control hydrophobic layer on hydrogels. [ABSTRACT FROM AUTHOR]

Novel water-dispersible donor–acceptor–donor π-conjugated bolaamphiphiles, having dibenzophenazine as the acceptor and heteroatom-bridged amphiphilic diarylamines as the donors, have been developed. The materials displayed a distinct photoluminescence color change in response to humidity in a poly(vinylalcohol) matrix. [ABSTRACT FROM AUTHOR]

Polymers with crystallizable side chains have numerous applications, and their properties depend on their crystal morphologies and phase separation. Structural analysis on a wide spatial scale plays an important role in controlling the thermal properties and higher-order structures of these polymers. In this study, we elucidated the melting and crystallization processes of copolymers with varying crystallizable side-chain fractions over a wide spatial range. Differential scanning calorimetry revealed that the enthalpies of melting and crystallization increased linearly with increasing crystallizable side-chain fraction. The results of wide-angle X-ray scattering indicated that the crystal lattice was hexagonal. Conversely, spherulite-like higher-order architectures with linear structures and radial spreading were observed in the highly crystallizable components, but no micrometer-scale structures were observed in the less crystallizable components. In situ small-angle X-ray scattering was used to elucidate the phase separation and mixing processes. Lamellar crystallites were observed at crystallizable side-chain fractions of >55 wt.%, whereas small crystallites were observed at fractions of <45 wt.%. At temperatures above the order-disorder transition temperature, density fluctuations caused by correlation holes were observed. These properties have a strong effect on the crystallizable side-chain fraction. [ABSTRACT FROM AUTHOR]