ABSTRACT
The effect of the surface charge of nucleation agents on the crystallization behavior of poly(vinylidene fluoride) (PVDF) has been investigated. Ion-dipole interaction between the positive surface of nucleation agents and the partially negative CF(2) dipoles of PVDF is established as a main factor for further lowering the free energy barrier for nucleation, and thus increasing significantly the crystallization kinetics. This is in contrast to the behavior observed for nucleation agents possessing either negative surface or neutral charges. Positive nucleation agents led to a remarkable increase in the crystallization temperature of PVDF (lower supercooling) as compared with that of neat PVDF. The dispersion of each type of nucleation agent is also important. The melting temperatures of nucleation agents need to be higher than the melting temperature of PVDF. The melting point and degree of crystallinity of PVDF can also be raised by using specific nucleation agents. The detailed crystallization kinetics and conformational changes of the PVDF chain have been investigated. With the addition of positive nucleation agents, the γ and ß chain conformations, instead of the α phase, dominate.
