Underlying mechanism of shear-banding in soft glasses of charged colloidal rods with orientational domains

Abstract

Soft glasses of colloidal rods ( fd-virus particles) with orientational domains were recently shown to exhibit inhomogeneous flow profiles [Dhont et al., Phys. Rev. Fluids 2, 043301 (2017)]: fracture and accompanied plug flow at small shear rates, which transits to gradient shear-banding on increasing the shear rate, while a uniform flow profile develops at sufficiently high shear rates. These flow profiles coexist with Taylor-vorticity bands. The texture of such glasses under flow conditions consists of domains with varying orientations. The observed gradient shear-banding was solely attributed to the strong shear thinning behavior of the material inside the domains (henceforth abbreviated as domain-interior), without considering the texture stress that is due to interactions between the glassy domains. Here, we present new experiments on the shear-banding transition to assess the role played by the texture stress in comparison to the domain-interior stress. For a large concentration, well into the glassy state, it is found that both texture stress and domain-interior stress contribute significantly to the gradient shear-banding transition in the shear-rate region where it occurs. On the other hand, for a small concentration close to the glass-transition concentration, the domains are shown to coalesce within the shear-rate range where gradient shear-banding is observed. As a result, the texture stress diminishes and the domain-interior stress increases upon coalescence, leading to a stress plateau. Thus, a subtle interplay exists between the stresses arising from the structural order on two widely separated length scales from interactions between domains and from the rod-rod interactions within the domain-interior for both concentrations.

Structural Color from Cellulose Nanocrystals or Chitin Nanocrystals: Self-Assembly, Optics, and Applications

“…353 This alignment under shear is also responsible for a shear-thinning behavior in the rheological characterization of dilute suspensions, but with minimal structural formation upon shear. 354 Shear causes a statistical alignment in which CNCs spend, on average, more time along the direction of the flow, but additional behavior such as periodically tumbling, kayaking, log-rolling or wagging is also expected, 355,356 and as observed experimentally for CNCs 357 (or fd viruses 339,358 ) Chemical Reviews pubs.acs.org/CR Review and supported by theory and simulations. 359 In contrast, elongational flow, such as that occurring at the inlet of a bottleneck, causes an aligning torque on each CNCs, without tumbling.…”

Role of confinement in the shear banding and shear jamming in noncolloidal fiber suspensions

“…Commonly, only two gradient shear banding regions were observed for complex fluids, 51,52 including colloids, 53,54 surfactant solutions, 55 entangled polymers, 56,57 and dense granular suspensions. 58,59 Though shear banding has been implicated in various scenarios for particle-filled suspensions, such as strong shear thinning of yielding fluids, [60][61][62][63][64] shear-induced phase separation, 53,54,65,66 and shear-induced particle migration during shear thickening, 24 only a few experiments have observed three-banding regions under specific conditions, such as wall slip induced phase transition 67,68 and collective swarming of active fluids. 69 The first scenario for gradient shear banding necessitates strong shear thinning typically for yield stress fluids, [60][61][62][63][64] where two shear banding regions were typically observed.…”

“…The second scenario for gradient shear banding involves shear-induced phase separation behaviors (between isotropic and nematic), 53,54,65,66 typically for rigid rod/fiber suspensions or liquid crystals. However, the characteristic size of the nematic domains was typically larger than 150 times the fiber length.…”