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UNIFORM TO ACCELERATED CRYSTAL TWISTING TRANSITION IN DEUTERATE POLYETHYLENE/POLY (ETHYLENE-ALT-PROPYLENE) BLEND FILM
作者:張麗娜,程賀,史偉超,韓志超
關(guān)鍵字:asymmetric phase separation, crystallization assisted phase separation
論文來源:期刊
具體來源:chinese journal of polymer science
發(fā)表時(shí)間:2014年
A uniform to accelerated crystal twisting transition is observed in deuterate polyethylene/poly(ethylene-alt-propylene) (d-PE/PEP) blend film. And the band period is a function of initial d-PE concentration, quench depth and annealing time of phase separation. As Keith and Padden suggested, twisting of lamella is due to the unbalanced stress on its both sides, which can supply a satisfying explanation to banded spherulites formed in homogeneous systems. When it comes to d-PE/PEP blend system, in homogeneous 99% d-PE/PEP (weight fraction of d-PE) blend film, the formation of banded spherulite is observed as a result of uniform twisting of ribbon like d-PE lamella along the radial direction. With the amorphous PEP piling up, it transfers into accelerated edge-on to flat-on twisting due to crystallization assisted phase separation. The mechanism can be interpreted as following: d-PE molecules must inter-diffuse to the twisting growth front to continue the secondary nucleation and growth process. Meanwhile, the amorphous PEP molecules are rejected and accumulated at the twisting growth front. Once the d-PE lamella begins to twist because of unbalanced stress on both sides, the accumulated rubber phase at the growth front strengthens the unbalance and accelerates the edge-on to flat-on twisting. The concentration wave propagates further away with constant speed, and leads to concentric ring pattern with periodic nonuniform twisting along the radial direction. Since this is a kinetic effect, the band period can be controlled through initial d-PE concentration, quench depth and annealing time of phase separation. Our result shows that crystallization assisted phase separation can modify lamella growth kinetic pathway, thereby assisting concentric ring pattern formation