Giant intrinsic viscosity coefficients of two-dimensional macromolecules.

Abstract

The intrinsic viscosity coefficient <i>K</i>, which Einstein derived as 2.5 for dilute suspensions of spheres, increases markedly with deviation from spherical shape. Hence, <i>K</i> captures the topological characteristics of suspended particles and reflects the viscosity properties of colloidal dispersions. However, soft two-dimensional macromolecules (2DMs) deform and undergo topology transitions in flow fields, significantly complicating the viscosity properties of their suspensions. Here, we report exceedingly large <i>K</i> values of up to 3.01 × 10⁷ for dilute suspensions of 2D macromolecular graphene oxide (GO) because of its flat-scrolling transition in a shear field. We find that <i>K</i> values for flexible GO suspensions are three orders of magnitude higher than the theoretically predicted <i>K</i> values for a rigid platelet model. Theoretical analysis and experiments reveal that flexible GO undergoes a reversible topology deformation between flat and scroll conformations under shearing. This topology deformation greatly enlarges the hydrodynamic volume of GO, enabling the observed large values of <i>K</i> for flexible 2DMs compared with rigid platelets. We propose a new viscosity model to consider the topology deformation in soft 2DMs, which accurately predicts the large values of <i>K</i> and viscosities of GO suspensions. Our work offers different insights for the rheological study of complex suspensions and emphasizes the significance of complexity arising from topology deformation of individual suspended particles.