22. Melting of polymer crystals below the melting point(poster presentation,Soft Matter as Structured Materials)

この論文は国立情報学研究所の電子図書館事業により電子化されました。高分子鎖は折りたたまれて結晶化することにより、非常に薄い板状単結晶として析出する。そこでGibbs-Thomson効果により、平衡融点以下の温度で融解する。この融解キネティクスに関して、通常の結晶融解の常識に反する非常に特殊な振る舞いを実験的に見いだした。この振る舞いは高分子性に由来するエントロピー障壁により矛盾なく説明できる

Nucleation on active centers in confined volumes

Kinetic equations describing nucleation on active centers are solved numerically to determine the number of supercritical nuclei, nucleation rate, and the number density of nuclei for formation both of droplets from vapor and also crystalline phase from vapor, solution, and melt. Our approach follows standard nucleation model, when the exhaustion of active centers is taken into account via the boundary condition, and thus no additional equation (expressing exhaustion of active centers) is needed. Moreover, we have included into our model lowering of supersaturation of a mother phase as a consequence of the phase transition process within a confined volume. It is shown that the standard model of nucleation on active centers (Avrami approach) gives faster exhaustion of active centers as compared with our model in all systems under consideration. Nucleation rate (in difference to standard approach based on Avrami model) is equal to the time derivative of the total number of nuclei and reaches some maximum with time. At lower nucleation barrier (corresponding to higher initial supersaturation or lower wetting angle of nucleus on the surface of active center) the exhaustion of active centers is faster. Decrease in supersaturation of the mother phase is faster at higher number of active centers

First Direct Observation of Nano-nucleation and Homogeneous Nucleation from the Bulky Melt of Polymer(<Special Topic>Nucleation in Soft-materials)

X線小角散乱法により,技術的問題から80年近く困難であったナノ核生成の直接観察に世界で初めて成功した.ナノ核のサイズ分布f(N,t)を定量的に示し,ナノ核生成の実体を明らかにした.さらに,質量分布関数Q(N,t)を導入して,確率過程における新しい核生成の基礎方程式を提案した.これにより,古典的核生成理論によって提案された核生成の速度論的基礎方程式において,質量保存則を満たさないという重大な問題点を解決した.高分子バルク過冷却融液を,ある臨界の伸長歪み速度以上で結晶化させると,不均一核生成が均一核生成に変わり,形態がマクロな球晶構造からナノメートルサイズのナノ配向結晶体(nano-oriented crystals,NOC)に一変した.NOCは比強度(重量当たりの引っ張り強度)が鋼鉄の数倍で高透明性,高耐熱性を示す"超高性能高分子材料"であることが分かった.We succeeded in observing nano-nucleation by means of small angle X-ray scattering for the first time, which had been impossible to observe for about 80 years due to technical problems. We obtained size distribution f (N, t) of nano-nucleus and clarified the real-image of nano-nucleation. We also introduced "mass distribution function Q (N, t)" and proposed a new basic equation of the mass conservation law. This solved the serious problem in classical nucleation theory, where so called "fundamental kinetic equation" does not satisfy the mass conservation law. Polymer nucleation is the process of disentanglement and chain sliding diffusion along the chain axis due to the topological nature of chain-like polymers. We showed that nucleation and morphology changed under large elongational strain field: they discontinuously changed from heterogeneous to homogeneous ones and from spherulite to "nano-oriented crystals (NOC)", respectively, when the elongational strain rate increased larger than a critical elongational strain rate. Physical properties of the NOC were significantly improved

23. Origin of ringed polymer spherulites(poster presentation,Soft Matter as Structured Materials)

この論文は国立情報学研究所の電子図書館事業により電子化されました。高分子結晶が作る球晶に同心円状のリングパターンがみられる場合がある。球晶内の微結晶が成長方向を軸として捩れ相関を持つことが原因であるが、捩れの機構については未だ明らかでない。今回、成長界面のMullins-Sekerka不安定性と結晶に内在するキラルな歪みの結合により、リング周期が決定される機構を提案し、ポリエチレンのリング球晶について検証した

MOLECULAR WEIGHT DEPENDENCE OF LATERAL GROWTH RATE OF A SINGLE CRYSTAL OF POLYETHYLENE(Session III : Complex Fluids, The 1st Tohwa University International Meeting on Statistical Physics Theories, Experiments and Computer Simulations)

この論文は国立情報学研究所の電子図書館事業により電子化されました

Size distribution of folded chain crystal nuclei of polyethylene on active centers

Kinetic equations describing temporal evolution of the size distribution of crystalline nuclei of folded chain polyethylene on active centers are solved numerically. Basic characteristics of nucleation processes (the total number of supercritical nuclei and the size distribution of nuclei) are determined and compared with the experimental data. It is shown that even though the total number of supercritical nuclei coincides with the experimental data, the size distribution prediction fails. This is caused by the fact that the total number of nuclei (usually used in analysis of the experimental data), in contrast to the size distribution of nuclei, represents an integral quantity. Using the experimental data of the steady state size distribution of nuclei enables us to determine thermodynamic parameters (especially interfacial energies) of the studied system more precisely and consequently to correct kinetic parameters to get coincidence of kinetic model with the experimental data in both, the total number of supercritical nuclei and also the size distribution of nuclei

AFM observation of polyethylene single crystals: selective handedness of screw dislocations in a chair type

The three-dimensional morphology of polyethylene single crystals grown from dilute solution has been examined by atomic force microscopy. Single crystals were deposited on a soft ground of aqueous solution of poly(vinyl alcohol) (PVA) to avoid the collapse of thin lamellar crystals with thickness of 10 nm. The observation of single crystals on dried PVA clarifies the morphology of a chair type crystal as well as well-known hollow pyramidal type. It has been confirmed that the screw dislocations in the chair type follow a selection rule of the handedness in a manner to relieve the distortion in the chair type

Nucleation and size distribution of nucleus during induction period of polyethylene crystallization

The crystallization process from supercooled melt results in the formation of nanosize nuclei in the earlier stage (induction period) through subsequent attachment or detachment of repeating unit to nuclei. The size distribution of nucleus f (Nj, t) in the induction period of nucleation process from the melts has not been experimentally confirmed yet by direct observation. The reason is that the number density of nuclei ν is too small to be detected experimentally. In our previous work, we showed the direct evidence of nucleation experimentally by means of small angle x-ray scattering (SAXS) technique. Further we have succeeded to observe the nucleation and f (Nj, t) of polymer crystallization from the melts by SAXS using synchrotron radiation. We increased ν by adding a nucleating agent to a polymer (polyethylene). The time evolution of f (Nj, t) was observed for the first time. © 2005 American Institute of Physics