Scale-dependent particle diffusivity and apparent viscosity in polymer solutions as probed by dynamic magnetic nanorheology. Issue 32 (27th July 2020)

• Record Type: Journal Article
• Authors: Hess, Melissa; Gratz, Micha; Remmer, Hilke; Webers, Samira; Landers, Joachim; Borin, Dmitry; Ludwig, Frank; Wende, Heiko; Odenbach, Stefan; Tschöpe, Andreas; Schmidt, Annette M.
• Is Part Of: Soft matter. Volume 16:Issue 32(2020)
• Page Start: 7562
• Page End: 7575
• Publication Date: 2020-07-27
• Subjects: Soft condensed matter -- Periodicals; 530.413
• DOI: 10.1039/c9sm00747d
• Languages: English
• ISSNs: 1744-683X

Abstract

Abstract : A systematic survey on magnetic particle nanorheology on polymer solutions using different particle sizes and geometries, and different driving modes. Abstract : In several upcoming rheological approaches, including methods of micro- and nanorheology, the measurement geometry is of critical impact on the interpretation of the results. The relative size of the probe objects employed (as compared to the intrinsic length scales of the sample to be investigated) becomes of crucial importance, and there is increasing interest to investigate the dynamic processes and mobility in nanostructured materials. A combination of different rheological approaches based on the rotation of magnetically blocked nanoprobes is used to systematically investigate the size-dependent diffusion behavior in aqueous poly(ethylene glycol) (PEG) solutions with special attention paid to the relation of probe size to characteristic length scales within the polymer solutions. We employ two types of probe particles: nickel rods of hydrodynamic length L h between 200 nm and 650 nm, and cobalt ferrite spheres with diameter d h between 13 nm and 23 nm, and examine the influence of particle size and shape on the nanorheological information obtained in model polymer solutions based on two related, dynamic-magnetic approaches. The results confirm that as long as the investigated solutions are not entangled, and the particles are much larger than the macromolecular correlation length, a good accordance between macroscopic and nanoscopic results, whereas a strong size-dependent response is observed in cases where the particles are of similar size or smaller than the radius of gyration R g or the correlation length ξ of the polymer solution.