非缠结对称缔合链在蠕变过程中的动力学行为研究

Creep Dynamics of Non-entangled Symmetric Associative Polymers

首先介绍具有摩擦系数分布的Rouse链的动力学分析方法,并检验了其应用于预测未缠结缔合高分子动力学行为的可行性.之后利用上述方法研究不同缔合点数量的高分子链分别在固定应变速率的启动剪切(start-up)和固定应力的蠕变(creep)测试过程中,链段的取向函数随时间的变化行为.阐明了缔合体系在蠕变条件下,高分子链从链段相对独立的运动到整链协同运动的转变机制.

In this study,creep dynamics of associative polymers is analyzed on a basis of Rouse model.The association sites,i.e.,the stickers,are introduced via increasing the segmental friction of the associative sites.First,we clarify the relationship between the Rouse model with frictional distribution and the sticky-Rouse model with stickers having fixed“lifetime”.Namely,we explain how to choose the friction coefficient so as to model the associative polymers with stickers of fixed lifetime.Comparison between the prediction of the Rouse model with frictional distribution and either the discrete or the continuous sticky-Rouse model rationalizes the choice.Second,we use the Rouse model with frictional distribution to analyze the conformational evolution of non-entangled symmetric associative polymers during the start-up shear and creep processes.During the start-up shear,the orientation function(representing an average segmental orientation of a given position of the chains)increases with time,and finally reaches the steady state.The orientation function increases from the ends to the center of the chains,akin to that of non-associative polymer chains.Nevertheless,we find a unique stepwise increase of orientation anisotropy at the sticky sites.We attribute this feature to the dynamic roles of the sticky and non sticky segments.Namely,the sticky segments are strongly oriented by the shear flow field,and the non-sticky segments confined between the sticky segments are forced to transmit the orientational force of the sticky segments.During the creep process with fixed stress,the evolution of the conformation function experiences obviously two stages.In the early stage,only the segmental motion is activated,where the sticky and non-sticky segments behave accordingly to their intrinsic nature,i.e.,the sticky and non-sticky segments increase and decrease the orientation function,respectively,so as to maintain the steady stress.In the second stage,the segmental motion extends gradually to the chain dimension and the orientation function of both the sticky and non-sticky segments achieve gradually to the steady-state.