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| Home > Publications database > Orientational Glasses and Phase Behavior of Charged DNA-Rods and their Response to Shear Flow |
| Talk (non-conference) (Invited) | FZJ-2022-04515 |
2022
Abstract: Long and thin, highly charged colloidal rods (fd-virus particles) exhibit a glass transition at a concentration for low ionic strengths, far above the isotropic-nematic coexistence region. The morphology of the system consists of chiral-nematic mesophases with different orientations. The dynamics of single particles within the domains is arrested due to initial caging of the charged rods by their neighbors through long-ranged electrostatic interactions. The microscopic dynamics of the orientation texture in domains is found to freeze at the same concentration where single particles are dynamically arrested [1,2]. Below the glass-transition concentration, the initial morphology with large shear-aligned domains breaks up into smaller domains, and equilibrates after typically 50–100 hours. Two dynamical modes are observed below the glass transition upon equilibration. On approach of the glass-transition concentration, the slow dynamical mode increases in amplitude, while the amplitudes of a fast and slow modes become equal at the glass transition [3-6]. In the first part of this talk I will present experimental results on the glass transition, the dynamics below the glass-transition, and the phase diagram in the fd-concentration versus ionic strength.The second part of the talk will be devoted to the flow behavior of fd-suspensions in the glassy state. Such suspensions exhibit stable inhomogeneous flow profiles, depending on the applied shear rate: fracture and plug flow at low shear rates, shear-banding at intermediate shear rates, and a linear profile at sufficiently high shear rate. These flow profiles coexist with Taylor vorticity bands [7,8]. The mechanism for shear-banding in these systems with a soft, long-ranged repulsive inter-particle potential is not related to shear-gradient induced mass transport that occurs in systems with a short-ranged interaction potential [9], but is due to the classic banding scenario related to strong shear-thinning behavior [7]. It is shown that there is a subtle interplay between the stress originating from inter-particle interactions within the domains and the texture stress due to inter-domain interactions [8,10]. References: [1] Phys. Rev. Lett. 110, 015901 (2013) [2] Soft Matter 9, 4401 (2013)[3] Soft Matter 10, 3311 (2014)[4] Scientific Reports 11, 3472 (2021), [5] J. Phys. Commun. 5, 065011 (2021)[6] J. Phys. Commun. 6, 015001 (2022)[7] Phys. Rev. Fluids 2, 043301 (2017)[8] J. Rheol. 66, 2, March 1st (2022)[9] Soft Matter 10, 9470 (2014) [10] J. Phys. Commun. 5, 045011 (2021)
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