Role of entanglement in nucleation and 'melt relaxation' of polyethylene
Role of entanglement in nucleation and 'melt relaxation' of polyethylene
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DOI：
10.1016/s0032-3861(02)00592-x
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发表时间：
2002-11
期刊：
影响因子：
4.6
通讯作者：
S. Yamazaki;M. Hikosaka;A. Toda;I. Wataoka;Fangming Gu
中科院分区：
文献类型：
--
作者：
S. Yamazaki;M. Hikosaka;A. Toda;I. Wataoka;Fangming Gu
An experimental formula of the nucleation rate I of polyethylene as a function of number density of entanglement νewithin the melt was obtained as I(νe)∝exp(−γνe), where γ is a constant. In order to obtain a functional form of I(νe), I is determined by changing νewithin the melt. The νewithin the melt can be changed when crystals with different lamellar thickness l are melted. It is shown that the νewithin the melt just after melting is related to l before melting. The νeof folded chain crystals (FCCs) is large, while that of extended chain single crystals (ECSCs) is very small. Therefore, strictly speaking, the experimental formula is a kind of ‘semi-experimental’ one. Because it is obtained by combining an experimental formula of I as a function of l before melting I(l) and a formula between l and νebased on the most probable model. It was found that the νedependence of I is mainly controlled by the topological diffusion process within the interface between the melt and a nucleus and/or within the nucleus not by the forming process of a critical nucleus. The slope of the plots of logI against ΔT−2was constant, irrespective of morphologies, FCCs and ECSCs, where ΔT is the degree of supercooling. From this fact, it was concluded that the fold type nucleus are formed from the melt of ECSCs as well as from the melt of FCCs. In our previous study, we found that I decreases exponentially with increase of annealing time Δt at a temperature above the melting temperature. From these results, we proposed a ‘two-stage melt relaxation’, i.e. fast conformational and slow topological relaxations. When the ECSCs are melted, extended chains within ECSCs are rapidly changed to random coiled chain conformation and then chains gradually entangle each other. We also proposed a formula, νe( Δ t)∝− ln { const. +A exp (− Δ t/τm)}, where A is a constant and τmis the ‘melt relaxation’ time.
