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1  Yonsei University


The rheology studies of complex fluid with deformable particles such as red blood cells (RBCs) are highly interested for a broad range of research works in biological systems, the cosmetic industries, mining and petroleum industries and home products. However, predicting the rheological behavior of soft particles in matrix is one of the most challenging and complicated problems in material and fluid sciences. The complication is arisen by the particles collision and interactions with the surrounding fluid. A full description of the rheology of soft particles requires a complete understanding of the deformation of particles itself [1], interactions among particles, interaction between the particles and the surrounding fluid [2], and interactions between channel and particles. Thus consideration of above factors can lead to a better understanding of the rheological behavior of suspensions with soft particles.


A suspension system of soft particles which is composed of a fluid-filled interior covered by an elastic membrane is simulated to study its rheological characteristics under various condition as shown in Fig. 1. In this study, the rheological behaviors of the soft particle suspension are observed with respect to several variations, for instance, shear rate, volume fraction, deformability of the particles, and various channel. A combination model of the three dimensional lattice Boltzmann method (LBM) and the immersed boundary method (IBM) are used to simulate these suspension systems.


With the aid of a numerical simulation, which can help in visualizing the particle behavior, and correlate it to rheological behavior of each particles, the physics behind the relative viscosity change was analyzed. To validate the soft particle model, the ratio of length to width for the stretching of soft particle was measured. For the single particle deformation in the flow, the boundary thickness was analyzed, which was related to the repulsive force critical for the interaction between the particle and wall, the effect of stiffness of RBCs on transit time in a microchannel was analyzed, which was proven to not be crucial for modeling of the soft particle. To see the interaction between wall property and suspension flow, soft particles in hydrophobic and hydrophilic surface microfluidic channels was simulated. To see the interaction among cells, red blood cells in shear flow with various aggregation condition was simulated


The time for cells to pass through the channel is measured at different values of shear modulus, along with analysis of the degree of deformation and transit time in Fig.2. Moreover, the velocity and deformation of cells as a function of boundary thickness and the effect of volume conservation stiffness were studied in Fig.3. The surface properties of the channel are changed using the tangential momentum accommodation coefficient on the channel boundary to set the hydrophobic surface in the simulation. The relative apparent viscosity is used to calculate systematic flow resistance in Fig.4. The results indicate that the flow rate and flow profile varied with respect to the surface property under a constant pressure gradient in Fig.5.