Dynamic viscoelasticity measurement was carried out for dilute and concentrated solutions of a water-soluble polysaccharide (SPS) extracted from soybean. The SPS solutions were able to be prepared up to the SPS concentration (c) of 30 wt% by using an ionic liquid 1-butyl-3-methylimidazolium acetate (BmimAc) as a solvent, while this “water-soluble” polysaccharide was actually soluble in water up to 3 wt%. The obtained dynamic viscoelasticity showed no rubbery plateau region, indicating that there was no entanglement coupling between SPS chains in the solutions. On the other hand, the c-dependence of the relative viscosity for the SPS solutions exhibited the critical concentration (cc) of ca. 9 wt% which in general corresponds to the onset of entanglement coupling between polymer chains in the solutions. The anomalous absence of the entanglement coupling in the SPS solutions above cc was attributed to the branching structure of SPS.
Fractional calculus is a useful mathematical tool to describe viscoelastic materials showing power-law relaxation behavior, characteristic of inhomogeneous systems. In this study, we applied the 3-elements fractional Maxwell model containing a power law element in addition to viscous and elastic elements to the viscoelastic properties of amorphous polymers. In the case of reorientation mode, which is the main relaxation process of the rubbery polymers, the 3-elements fractional Maxwell provides a relatively broad terminal relaxation than the Rouse-Zimm model, which has already been well-established for the viscoelastic response of linear polymers. This result could be attributed to the polymeric systems being well coarse-grained over a long-time scale. On the other hand, the model well described the frequency dependence of the complex modulus of the glassy component of amorphous polymers.
Nonlinear viscoelastic behavior of glassy poly(methyl methacrylate) (PMMA) subjected to high tensile creep stresses was studied. Right after the loading of creep stress, a rapid decrease of strain rate as a function of strain was observed, indicating behavior of linear viscoelastic solid. Then after showing a sharp minimum, the strain rate gradually increased due to nonlinear flow and reached to almost constant maximum values at steady flow state, and then slightly decreased. Strain range in which the nonlinear flow was observed did not strongly depend on the magnitude of creep stress and temperature, although magnitude of strain rate was obviously affected by these conditions. Nonlinear single relaxation time τ for the glass in the nonlinear flow range of strain was evaluated by means of a simple mechanical model. The nonlinear relaxation time τ decreased with increasing time t to a steady value appeared in the steady flow state. A quantity τ/t was found to be an almost unique decreasing function of strain independently of differences in magnitude of creep stress and temperature. This characteristic dependence of relaxation time τ on strain was considered as a result of a constant decreasing slope of τ-t relation, which slightly depends on the magnitude of stress, during transient flow state under constant high stresses.
We investigated the relation between modulus enhancement and reduction of free volume of polycarbonate (PC) by addition of low-mass molecules (LMs) with various sizes and concentrations. The modulus enhancement of PC, which is called “antiplasticization”, is due to the restriction of local chain motion of PC by the LM additives. For PC and antiplasticized PC, the free volume was evaluated at various temperatures below the glass transition temperature through positron annihilation lifetime spectroscopy. The results showed that the free volume decreased in the presence of LMs at all the temperatures in the glassy region, but the free volume of antiplasticized PC became close to that of pure PC at the rotational relaxation temperature for LMs. This result indicated that the LM dynamics strongly affected the PC free volume, which determined the degree of modulus enhancement. Furthermore, storage moduli of PC blends were compared for various LMs at different concentrations. The comparison showed a universal relation between the PC storage modulus at 25 °C and the LM molar concentration. This result suggests that each LM restricts the local motion of PC to the same degree independently of the molecular size.
The crystallization behavior and rheological properties of PP in addition of polysilane which consists of Si-Si conjugation as a main chain were investigated. From the DSC measurement results, it was found that the crystallization temperature, melting point, and equilibrium melting point of PP decreased monotonically as the amount of PMPS added increased. On the SAXS measurement, the addition of PMPS reduces the long period and lamella thickness of PP crystals, while increasing the amorphous phase thickness and reducing the surface free energy. In the crystallization process, the temperature profile of the relative crystallization degree was shifted to the long-term side by adding PMPS to PP, and the crystallization was delayed. As a result of analyzing the compatibility between PP and PMPS with reference to the method of Nishi-Wang, it was deduced that these materials were compatible. From rheological measurements, it was found that PP in the molten state induces a decrease in viscosity due to the addition of PMPS, and the temperature dependence of the change also increased. Regarding the molecular motion in the solid state, it was found that the segment motion of PP near Tg was improved by the addition of PMPS. Finally, the uniaxial tensile test showed that the PP elastic modulus and yield stress decreased, but the elongation at break improved significantly.
Focusing on the melting process of poly(phenylene sulfide) (PPS) crystals, one of the high-performance resins with a very wide range of applications, we attempted to clarify the melting process and derive the equilibrium melting temperature with structural analysis using X-ray scattering and thermal measurements. Two melting points were observed in the crystallized PPS films by DSC measurements. We focused on the low-temperature melting point, in situ small-angle and wide-angle X-ray scattering measurements using synchrotron radiation and DSC thermograms indicate the melting of microcrystals because of thickening of the amorphous part from small-angle X-ray scattering results. In addition, the Hoffman-Weeks plot based on the results of fast scanning calorimetry showed that the melting temperature is almost parallel to the straight line where melting temperature and crystallization temperature are equal, indicating that the melting is of a metastable structure. The melting point on the high temperature side was attributed to the melting of lamellar crystals. The equilibrium melting point was derived from the Hoffman-Week and Gibbs-Thomson plots as 318 °C.
We report experimental findings of spontaneous perpendicular orientation and successive kinking of microdomains in film specimens of block copolymer by solution cast using selective solvent. These phenomena were firstly found out by our experiments. It is notable that only conducting solution cast is a straightforward and sophisticated to obtain perpendicular orientation of cylindrical and lamellar microdomains because mainly reported methods utilize application of external fields such as electric, magnetic, or temperature gradient field. The key point of this method exists in utilization of selective solvent which possesses different degrees of solubility for two respective components of block copolymer. The specimen used is a polystyrene-block-poly(ethylene-butylene)-block-polystyrene triblock copolymer and selective solvents were n-heptane, dichloromethane, and toluene, which are selectively good solvents for PEB (poly(ethylene-butylene)), PS (polystyrene), and PS, respectively. Furthermore, mixtures of n-heptane and dichloromethane were used for more precise control of the degree of selectivity. To analyze the nano structures in the as-cast and annealed specimens, transmission electron microscopy and two-dimensional small-angle X-ray scattering (2d-SAXS) measurements were conducted at room temperature. As a result, the edge-view 2d-SAXS pattern relevant to the kinking was obtained for the as-cast specimens by using toluene for the solution cast. To explain the mechanism, schematic illustrations are presented with the idea of spontaneous parallel orientation of cylinders or lamellae, and successive kinking during further solvent evaporation.
This study investigates the characteristic endothermic peaks of ionomers, Ti, appears at lower temperature than the melting point. We evaluate the thermal properties of ionomers under various heat treatment conditions with DSC. The Ti peak temperature and endothermic peaks area increase with longer heat treatment time. For more detailed analysis, we evaluate the nanoscale structure with small-angle and wide-angle X-ray scattering measurements. The correlation length between polyethylene crystals increases with increasing temperature above Ti. The results showed that the Ti peaks are very sensitive to heat treatment conditions, especially to the nanoscale structure. Furthermore, the radius of core of ion-aggregates and that of the immobile polymer layer was very sensitive of temperature. From these results, precise analysis also showed that the change in Ti peaks is due to the important role of molecular motion in the amorphous regions between crystals. We also showed that the appearance of Ti peaks depends on the interaction of ions with the carboxylic acid ion of polymers.
Strength of structural materials used in corrosive environment will be lowered compared with that of materials used in air due to the effect of corrosion fatigue. In the previous study, fatigue tests on a type 440C stainless steel, which has been used as a part of automobile fuel injection system, in air and petrol environment were conducted by means of a small sized smooth specimen and a fatigue testing machine for the specimen performable in corrosion and flammable liquid under push-pull loading at high frequency region. However, it was difficult to investigate the effect of corrosion due to the difference of fracture morphology. In this study, fatigue tests on the same material were conducted by means of a small sized specimen with notch for matched fracture origin in air and deteriorated petrol under the same test condition. The fracture on fatigue tests with notched specimens initiated from specimen surface regardless of the test environment. In petrol that contains methanol, fatigue fracture was caused on lower stress level because minor intergranular cracks were originated by the effect of corrosion. Fatigue lives of flat specimen were correlated using the size of the inclusions and they were correlated with high accuracy. Fatigue limit was also estimated. It was confirmed that fracture origin was changed to the surface due to immersion to petrol that contains methanol. The relationship with the stress state in notch part and fatigue failure mechanism was discussed in detail.
At Construction sites, curing sheets for temporary scaffolding is used to prevent the building materials from falling and dust from scattering. In this study, it was examined that by using the curing sheet whose inside is black with good transparency and whose outside is white, it is possible to realize an environment with good transparency from the internal space and an environment with good transparency from the external space at night. Within the measurement range of this study, the white-and-black curing sheet has good transparency from internal space like the black curing sheet and has better transparency from internal space at night than the white and gray curing sheets. Further, there is no difference in transparency from external space at night of all color of curing sheets. The white-and-black curing sheet has a small change in the feeling of the internal space at night before and after the curing sheet is installed.