MECHANOCHEMICAL DEGRADATION IN TRANSIENT ELONGATIONAL FLOW

作者：NGUYEN TQ^*; KAUSCH HH

来源：Advances in Polymer Science, 1992, 100: 73-182.

Polymer molecules respond to the application of stress by disentanglement, chain orientation and bond rupture. Being the last step in this series of events, the efficiency of flow-induced mechanochemical degradation depends markedly on the details of the pervading flow field. From the results of fluid mechanics, it is usual to distinguish degradation in simple shear flow from degradation in elongational flow. Polymer dynamics require a further subdivision between transient elongational flow, characterized by a short residence time (less than the chain relaxation time tau1) in the high strain rate region, from quasi-steady-state elongational flow which possesses a stagnation point and a long residence time (much greater than tau1). This chapter reviews the main factors which influence the degradation kinetics in transient elongational flow, exemplified by flow through a narrow contraction and ultrasonic irradiation. The experimental results reveal a fundamental difference in the kinetics of chain scission in transient and stagnant conditions. Differences in the characteristic residence time prevalent in each type of flow permits one to probe the different stages of the chain unravelling process up to the point of bond rupture. It is suggested that the intricate degradation behavior observed in transient elongational flow stems from the compact nature of the weakly deformed molecular coil. This favors intramolecular interactions during the dynamics of deformation.

• 出版日期1992