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
發表時間：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