Isao Wataoka

The sol-gel transition of gellan gum aqueous solutions in the presence of various metal salts

Gellan gum undergoes gelation by forming domains composed of associated double helices. Gellan gum aqueous solutions were prepared with or without adding various metal salts, and their gel-sol transitions were observed by small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC). The SAXS results are analyzed in terms of the molecular models of associated double helices, and the DSC endo-thermic peaks are attributed to the possible dissociation processes of the domains formed upon gelation. The mechanism of the gel-sol transition is discussed from the view point of the role of metal cations.

Structural characterization of polymacromonomer in solution by small‐angle x‐ray scattering

The polymerization of macromonomers provides polymers of extremely high branching density with regular branch length, branching number and branching interval. The intrinsic shape and size of these polymacromonomers were evaluated by small-angle X-ray scattering. The conformation of the backbone and side-chains was discussed. An oblate ellipsoid of revolution was proposed as an approximate shape of the polymacromonomers at a low degree of polymerization by scattering profile fitting. An elliptical cylinder was found to outline the polymacromonomer in solution at larger degrees of polymerization. The 3D molecular model of a polymacromonomer with a low degree of polymerization (DPM=7) suggested a random coil conformation for the backbone and side-chains. The conformational change of the backbone chain is speculated to take place when the total degree of polymerization exceeds a certain limiting value, where the polymacromonomer is represented by a molecular bottle brush as seen by light-scattering measurements. ©1997 SCI

Direct Evidence of Nucleation During the Induction Period of Polyethylene Crystallization by SAXS

Direct evidence that nuclei are formed during the induction period of crystallization is obtained for the first time by means of small-angle X-ray scattering (SAXS). Polyethylene (PE) was used as a model crystalline polymer. The nucleating agent was mixed with PE in order to increase the scattering intensity I x from nuclei as large as 104 times bigger than usual. I x increased soon after quenching to the crystallization temperature from the melt and saturated after some time. A new theory is proposed to estimate the size of the nuclei N, the number density distribution of nuclei with N at time t, f(t,N), and the induction time τ i, by analyzing the SAXS scattering intensity. The volume-averaged size of the nuclei was nearly the same as that of critical nuclei and does not change so much with time during the induction period. Lamellae start stacking much later than nuclei start forming.

Nucleation and Morphology of Polyethylene Under Shear Flow

Effect of the shear flow (γ˙=0.5∼5 s−1) on the nucleation and on the morphology of polyethylene (PE) during crystallization from the melt was studied by means of polarizing optical microscopy and small angle X-ray scattering. In order to analyze the results by the nucleation theory, we observed the effect of shear flow on the equilibrium melting temperature The under shear flow and that under quiescent state are almost the same, Therefore, the shear flow does not affect the The “heterogeneous” primary nucleation rate (I) and the induction onset time of nucleation (τ onset) of the isolated crystals under shear flow are also almost the same as those under quiescent state. The heterogeneous primary nucleation means that isolated nuclei are sporadically generating from the melt with the aid of heterogeneities such as nucleating agents. After the generation of primary nuclei, the “shish” were generated independent of the primary nucleation. We found that the shish were formed by the chain elongation caused by the velocity difference between polymer chains and dust particles, etc. After that, we observed that the “kebabs” were formed on the shish. It was found that the nucleation from the melt after melting of the “shish-kebabs” (at melt annealing temperature T max=160°C for 5 min) was accelerated compared with the ordinary melt crystallization after melting of folded chain crystals. This indicates that the “solid memory effect” of the former solid is significant. This is because of the low entanglement density within the melt of shish kebabs.

Effect of reaction pH and CuSO4 addition on the formation of catechinone due to oxidation of (+)-catechin

A novel hair dyeing technique being milder and safer for a human body is desired. The oxidation product of (+)‐catechin, catechinone, was invented as a safer dyestuff for hair colouring under such the situation. The preparation of catechinone by a chemical oxidation is a practical way and the objective of the study is clarify the effect of the solution pH and in the presence or absence of Cu2+ on the formation rate and yield of catechinone in order to improve the efficiency of the dye formation. The catechinone formation was monitored by ultraviolet‐visible spectroscopy. Catechinone was prepared chemically from (+)‐catechin in aqueous solution with O2 gas introduced over a pH range of 7.1–11.7. The rate and amount of the dye formation increase with increasing pH. Dissociation of the hydroxyl group of the catechol part of (+)‐catechin is significant for the oxidation of (+)‐catechin and promotes the dye production. This is because the deprotonated (+)‐catechin has a higher reactivity with O2. The production of catechinone is accelerated by the addition of CuSO4 and the production rate reaches the maximum at pH = 8.8. (+)‐Catechin ‐ Cu2+ complexes are formed and the formation promotes the oxidation of the catechol part of (+)‐catechin at pH ≤ 8.8. On the other hand, the complex becomes too stable to proceed for the oxidation reaction at pH > 8.8.

Grain coarsening on the free surface and in the thickness direction of a sphere-forming triblock copolymer film

Controlling a block copolymer “grain”, in which the microdomains are regularly ordered in a single lattice, is important for developing high-performance polymeric materials. This is because the grains, which are several micrometers in size, can directly affect the properties of the materials. In this regard, we focused on grain coarsening on the free surface and in the thickness direction of a sphere-forming triblock copolymer film. We evaluated the grain size on the free surface using atomic force microscopy combined with image processing, and in the thickness direction, we used small-angle X-ray scattering edge-view measurements. It was found that the grain growth in the direction parallel to the free surface was very slow in the early stage of thermal annealing. Then, the grain growth shifted to a rapid growth mechanism with a power-law relationship (grain size ~tα, with α = 0.7) after ~30 min. Based on the value of the growth exponent α, the grain growth mechanism is considered to fall between the random and deterministic processes. In contrast, for the thickness direction, a much larger value (α = 1.72) was obtained. For such a large α value, it is impossible to consider the growth mechanism of the grain within the conventional to framework of the growth of domains and droplets. Therefore, our results may require a new framework to explain the behavior of the grain growth in the spherical microdomain system. Another notable finding is that the thickness of the oriented layer near the free surface or near the surface in contact with the substrate can be as thick as 9.5 µm, which is substantially larger than the reported values of the propagation distance of surface-induced orientation of microdomains in block copolymers. Based on the results of the current study, it is speculated that grain growth serves as a propagator for the regular ordering of spherical microdomains and the orientation of the lattice.The grain size was quantitatively evaluated on the free surface, and in the thickness direction. The grain growth on the free surface was very slow in the early stage of thermal annealing, then it shifted to a rapid mode with a power law (~t0.7). While in the thickness direction, the growth followed a power law of t1.72 until 1180 min, then it shifted to a slow mode with t0.21. Furthermore, the oriented layer near the free surface was found to be as thick as 9.5 µm, indicating that grain growth serves as a propagator for the regular ordering of spherical microdomains and orientation of the bcc lattice.