ABSTRACT:Molecular weight (M) dependence of the primary nucleation rate (I) of an extended chain single crystal of polyethylene crystallized at high pressure (P=0.4 GPa) was studied. We obtained for the first time an experimental formula that 1rxM-1 which we named "power law of primary nucleation". We showed a well-known experimental formula that I= 10 exp( -K/11T 2 ), where IO is a constant proportional to the diffusion constant of molecules (D), K is related to the activation free energy for forming a critical nucleus (!:iG*) and l:!.T is the degree of supercooling. We showed that only / 0 rxD decreases with increase in Mand K does not depend on M. From this results we concluded that M dependence of I is mainly controlled by the "chain sliding diffusion" process not by the formation process of a critical nucleus, that is, l(M) rxD(M)rxP,(M) and l:!.G* =const. Here D can be regarded as an "expanded diffusion constant" and P, is a survival probability defined in "chain sliding diffusion" theory presented before by one of authors (MH). Based on these results we proposed a "chain sliding diffusion theory of primary nucleation" that the primary nucleation is a process of "chain sliding diffusion" within the nucleus which requires disentanglement of molecular chains within the interface between the nucleus and the melt. The theory explained well the observed power law.KEY WORDS Nucleation / Nucleation Rate/ Molecular Weight /Polyethylene/ Power Law / Sliding Diffusion/ Primary nucleation is important onset stage 1 in crystallization of materials from an isotropic phase, such as the melt, the solution, gas and amorphous solid or from other phases, such as liquid crystalline one. The primary nucleation mechanism of atomic or low molecular weight systems has been studied well, 2 -5 while that of polymers has not been studied well and has been left unsolved for long years. 6 -10 (FCC and ECC), that is H = 1.8 and 0. 7 for FCC and for ECC, respectively. From this result, it is concluded that chain sliding diffusion on the interface between the melt and crystal controls the M dependence of the V (Figure 2). Another purpose of this work is to make clear if the "power law" can be also found in M dependence of nucleation rate or not.It is obvious that the molecular weight (M) is one of the most important parameters of poymer systems and it has been well known that M strongly affects the nucleation process of polymers, which strongly controls the crystallization behaviors. But the M dependence of polymer nucleation has not been studied well as far as authors' knowledge, therefore the mechanism of it has not been solved at all, although it is very interesting and important for both polymer science and technology to solve it.The main purpose of this work is to show a reliable experimental formula of M dependence of the primary nucleation rate (I) of polyethylene (PE) for the first time and to propose a new mechanism of the M dependence of the primary nucleation which we will name "chain sliding diffusion theory of primary nu...

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SummarySubcellular localization of calcium in the cells of the abscission layer and adjacent tissues was investigated electronmicroscopically by a Slocum and Roux's antimonate precipitation method using leaf explants of Calamondin (Citrus madurensis Lour.). Calcium localization, which was detected as electron-dense small particles, was determined by comparing the specimens which were fixed with fixatives with or without potassium antimonate. In fresh or IAA-treated explants only a few particles were present in the cells of the abscission layer along the plasmalemma and in the cytoplasm. In the explants which underwent some senescence, more particles were present along the plasmalemma and in the middle lamella of the cell wall, and a few in the cytoplasm and in the vacuole. In abscising explants, which were treated with trifluoperazine (TFP), abundant particles were present in the degenerated middle lamella. The role of calcium in senescence and abscission is discussed.