Colloid particle transport in a microcapillary: NMR study of particle and suspending fluid dynamics

• NMR ‘active’ colloidal particles at 22 vol% flowed through a μ-capillary
• Simultaneous measurement of particle and suspending fluid phase dynamics
• Dynamics of suspending fluid contains particle structure information
• Shear induced migration within μ-capillaries
• Results provide experimental data for further investigation and model verification

Precise manipulation of the hydrodynamic interaction between particles is particularly important for operation of microfluidic devices. Shear-induced migration gives rise to dynamical patterns within the flow that have been observed in a range of systems. In this work NMR ‘active’ colloidal particles (a=1.25 µm) at volume fraction of 22% in an aqueous phase are flowed through a µ-capillary (R=126 µm) and the transport dynamics of the particle and suspending fluid phases are studied using dynamic NMR techniques. Simultaneous interrogation of shear rheology of the suspending fluid and particle phases of colloidal suspensions is presented. The dynamic behavior of the suspending fluid is shown to carry within it information about the structure of the colloidal particle ensembles on the time scales investigated (Δ=25 ms→250 ms) providing rich experimental data for further investigation and model verification. The importance of determining the particle concentration profile within μ-capillaries is explicitly demonstrated as shear induced migration causes significant concentration gradients to occur at strong flow conditions (i.e. Pep=270).