Orientation dynamics of dilute functionalized graphene suspensions in oscillatory flow

Abstract

The dynamics of molecularly thin graphene sheets in transient flows are important to understand their behavior in suspension and during processing. Scattering dichroism is used to evaluate changes in the orientation distribution function in dilute suspensions. To evaluate if the graphene sheets behave as flexible sheets or as more rigid flat particles, the results are compared with numerical computations of the single-particle Smoluchowski equation for flat spheroidal particles. In particular, the evolution of the orientation angle in oscillatory flows as a function of increasing amplitude is studied. The results show that even when taking an average rotational diffusivity, the results for the polydisperse graphene sheets show all the hallmarks of the motion of rigid disks, including a frequency doubling of the time-dependent orientation signal. The results indicate that the motion of functionalized graphene sheets in suspension is consistent with flat rigid objects.

Nonlinear “oddities” at the percolation of 3D hierarchical graphene polymer nanocomposites

“…This fits within the framework of both the FT and Chebyshev decomposition results obtained for ϕ = 3.5 wt%. While, thus far the discussion has been overwhelmingly concentrated on conformational and interfacial aspects, the nonlinear dynamics could be dominated by the network orientation dynamics, e.g., see Natale et al (2018). In a first approximation, it could be conjectured that due to the gradual nature of chain conformation and confinement, such effects could be L/SCB PP/HrGO 3[origin = c]90Q 0 (ϕ)/Q 0 (0) ∝ ϕ, e 3/1 ∝ ϕ, v 3/1 ∝ 1/ϕ ϕ < 0.8 wt% MAOS: I 3=1 ∝γ 2 0 e 3/1 > 0; v 3/1 > 0 ϕ = 0.8 wt% MAOS: I 3=1 ∝γ 2 0 weak relative increase in Q 0 (ϕ)/Q 0 (0) e 3/1 > 0; v 3/1 ≈ 0, especially for ω = 0.6 rad/s ϕ = 1 wt% MAOS: I 3=1 ∝γ n 0 , n = n(ω) (ϕ ≈ ϕ c ) n ≈ 0.7 for ω = 0.6 rad/s; n ≈ 1.1 for ω = 1 rad/s; n ≈ 2, for ω > 2 rad/s significant relative increase in Q 0 (ϕ)/Q 0 (0) e 3/1 > 0; v 3/1 = v 3/1 (ω) v 3/1 < 0 for ω < 1 rad/s (v 3 < 0) v 3/1 > 0 for ω > 2 rad/s (v 3 > 0) v 3/1 weak dependence on γ 0 1 < ϕ < 3.5 wt% SAOS-MAOS: I 3=1 ∝γ n 0 , n = n(ω, γ 0 , ϕ) e.g., ϕ = 1.5 wt%: for ω < 2 rad/s, γ 0 ∈ [1, 10] %, n ≈ 0; γ 0 ∈ [10, 40] %, n = 2 for ω ≥ 2, → n = 2 e 3/1 > 0; v 3/1 = v 3/1 (ω, γ 0 , ϕ): e.g., ϕ = 1.5 wt%: for ω < 2 rad/s, γ 0 ∈ [10, 40] %, v 3/1 < 0; γ 0 > 40%, v 3/1 > 0 for ω > 2, v 3/1 > 0 ϕ = 3.5 wt% I 3=1 ∝γ n 0 ; with increasing γ 0 : n ≈ 1.1, n ≈ 0.2 and n ≈ 0.4 significant relative increase in e 3/1 , v 3/1 perhaps associated dominantly to the elastic stiffening response.…”

Hydrodynamic slip can align thin nanoplatelets in shear flow

“…The validity of the theory discussed here could be tested by measuring experimental observables that are sensitive to secondorder statistical moments, such as the 'degree of orientation'. The 'degree of orientation' of the particles, can be assessed by rheooptics experiments [64][65][66] . Contrarily, the average particles orientation angle may not be ideally suitable for discriminating between rotating and aligned particles because highly elongated plate-like particles are expected to align with the flow in a timeaverage sense regardless of the hydrodynamic slip 16,67 .…”

Oscillatory Shear Response of the Rigid Rod Model: Microstructural Evolution

“…44−46 Wagging dynamics was observed at finite Wi numbers and at De number equal to or above D r . 45,46 In the presence of the excluded volume potential, the situation changes drastically as soon as we reach nematic state. In this section, all the results are obtained in nematic state U = 6.66 and at the onset of LAOS, Wi = De = 1.…”

“…In the absence of excluded volume potential, the microstructural dynamics was previously investigated. − Wagging dynamics was observed at finite Wi numbers and at De number equal to or above D r . , …”