A uniform to accelerated crystal twisting transition is observed in deuterate polyethylene/poly(ethylene-

alt

-propylene) (d-PE/PEP) blend films. 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 lamellae 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.