Paper Number
PL2
Session
Plenary Lectures
Title
Molecular rheology and synthetic chemistry: A critical partnership for designing flow-responsive matter
Presentation Date and Time
October 22, 2019 (Tuesday) 8:30
Track / Room
Plenary Lectures / Room 306
Authors
- Vlassopoulos, Dimitris (FORTH, Institute of Electronic Structure & Laser)
Author and Affiliation Lines
Dimitris Vlassopoulos
Institute of Electronic Structure & Laser, FORTH, Heraklion 70013, Greece
Speaker / Presenter
Vlassopoulos, Dimitris
Text of Abstract
An intimate, molecular-level characterization of soft materials is crucially important for understanding their response to external fields. This, in turn, allows tailoring rheology at the molecular scale and designing materials, which frequently relies on bridging polymers and colloids, with desired properties. We discuss this singular interplay of synthetic chemistry and rheology in the context of two material classes. The first is multiarm star polymers, a paradigm for soft colloids with repulsive interactions. We highlight the decoupling of polymeric and colloidal contributions to their viscoelastic response in solutions and in the melt. Mixing such soft colloids is a powerful means of tuning their flow properties, leading to a variety of phases from liquid to glasses and gels. The associated transitions are understood in the context of effective interactions and the osmotic compression of stars. Examples of star – linear polymer mixtures are discussed. Introducing attractions offers a new strategy for obtaining soft patchy particles with complex, albeit tunable rheology. The resulting understanding can be framed into simple dynamic state diagrams and serves as a unifying guide for exploring the hybrid dynamics of soft materials with practical interest, for example grafted nanoparticles. A second material class comprises architecturally complex macromolecules. We address aspects of the dynamics of entangled combs and linear-ring polymer mixtures. The shear and extensional rheology of the former exhibit signatures of hierarchical relaxation due to dynamic dilution. The threading of the rings is responsible for the viscosity enhancement of the linear matrix in the latter case. Shear viscosity and normal stress differences are dominated by the linear chains contribution, which is very different from that of rings. These findings may improve our understanding of entangled polymer dynamics with implications for diverse applications ranging from materials processing to biological function.