Characteristic spatial scale of vesicle pair interactions in a plane linear flow

Abstract

We report the experimental studies on interaction of two vesicles trapped in a microfluidic four-roll mill, where a plane linear flow is realized. We found that the dynamics of a vesicle in tank-treading motion is significantly altered by the presence of another vesicle at separation distances up to 3.2-3.7 times of the vesicle effective radius. This result is supported by measurement of a single vesicle back-reaction on the velocity field. Thus the experiment provides the upper bound for the volume fraction φ = 0.08-0.13 of noninteracting vesicle suspensions.

Long-range hydrodynamic effect due to a single vesicle in linear flow

“…The effect of a single vesicle undergoing tank-treading motion in a planar linear flow remains significant up to a distance of about 4 effective vesicle radii. This value is consistent with the separation distance between two tanktreading vesicles in the same flow, at which their dynamics is altered [5]. Unfortunately, an attempt to reproduce numerically the experimental result on the dependence of the root-mean-squared fluctuations of the deflated vesicle inclination angle as a function of distance from a spherical one, was not successful so far and resulted in very scattered data.…”

“…The images were then filtered by a Laplace filter using Gaussian second derivatives [13], and processed using Gpiv [14] at interrogation windows of 32 × 32 pixels (corresponding to about 8.6 × 8.6 µm 2 ) with 50% overlap. [5] The 2D numerical model used here was introduced in Ref. [6].…”

Continuum- and particle-based modeling of shapes and dynamics of red blood cells in health and disease

“…92 Collective dynamics of many vesicles has also been considered, 93, 94 but only to a limited extent and a systematic numerical study of suspension rheology is still lacking. Such simulations are needed to interpret the experiments on hydrodynamic interactions between vesicles 95 and the effective viscosity of suspensions of RBCs and vesicles, 96 which was found to depend non-monotonically on λ.…”

Dynamics and rheology of vesicle suspensions in wall-bounded shear flow

“…Second, viscosity measurements require a minimum volume fraction φ of vesicles, typically 5% to 10%, and are therefore difficult to extrapolate to the dilute limit [13]. Indeed, experiments have been performed recently [14] which demonstrate that vesicle interactions become relevant for the viscosity for φ around 10%. Therefore, we study here the rheology of vesicle suspensions in the "semi-dilute" regime, where particle interactions are important, but particles are not yet densely packed into a glassy state.…”

“…Following the experimental work in refs. [13,14], we study the interaction between two vesicles with A * = 0.8 in the TT regime (λ = 1.0). Figure 4 displays the relative vertical displacement of the centers of mass ∆Y = y cm1 − y cm2 during scattering with respect to the horizontal displacement ∆X = x cm1 − x cm2 , where (x cm1 , y cm1 ) and (x cm2 , y cm2 ) are the positions of the centers of mass of the two vesicles, for three different shear rates γ * = 2.0, 5.0, and 10.0.…”