Rheological characteristics of the theta-shaped polymer under shear flow

Abstract

We present the structural, dynamical, and rheological behaviors of theta chains according to the solution type and the molecular architecture, using extensive bead-rod Brownian simulations, and compare them with the corresponding pure ring chain. Through detailed analysis of the properties of theta chains in each solution system, we found that theta chains have their own chain structure for each solution system and, accordingly, a characteristic dynamical behavior in each solution. For example, due to the absence of intra and intermolecular interactions in the free-draining solution system, the theta chain can have a fully stretched structure and can rotate like a conventional linear chain. On the other hand, due to the presence of intra and intramolecular interactions in the dilute solution system, the theta chain can have a spread (or extended) chain configuration that is aligned parallel to the flow-vorticity plane under shear flow, resulting in a two dimensional (2D) planar sheet-like chain structure. Thus, the theta chain alternates between the 2D planar sheet structure and the folded sheet structure during the chain rotation and tumbling cycle. We also found that the structural, dynamical, and rheological properties of the theta chains are highly dependent on the existence of a bridged linear part of the theta chain irrespective of the solution type. Since the bridged part of the theta chain physically prevents chain extension induced by a strong shear flow, the theta chains tend to have a less deformed chain structure than the corresponding pure ring chain. Depending on the length of the branched part of the theta chain, the rotation and tumbling behavior of the theta chain are greatly modified.