2003 -03 -19
10 :30 at ML J22

A universal quantitative requirement for the formation of the shish-kebab structure

Jan van Meerveld

Institute of Polymers, ETH Zurich

The formation of the shish-kebab morphology is known for about 40 years. However a good understanding which physical process governs the development of these structures is still missing. Based on experiments the development of shish structures is found to correspond to a transition from weak to large rotational isomerization due to chain stretching. For different flexible polymers, and identical polymers of different chain length, this transition follows a universal behavior when expressed in terms of the reduced molecular chain extension. Also for the formulation of the shish-structures in uniaxial deformed poly(ethylene therephthalate) and different natural rubbers, as revealed by real-time simultanious WAXS measurements, is found to follow the same universal behavior. These findings indicate that the shish-kebab structure develops only if a critical molecular chain extension is achieved by the applied flow or deformation field. The formation of a shish during the flow is explained from the observation that the requirement for orientational and conformational order of the chain are satisfied in a more deterministic, rather than a pure stochastic manner. Moreover the nucleus may not be 'trapped' in some metastable state, which limits the nucleation rate.