title: Microfluidic quadrupole and floating concentration gradient.
abstract: The concept of fluidic multipoles, in analogy to electrostatics, has long been known as a particular class of solutions of the Navier-Stokes equation in potential flows; however, experimental observations of fluidic multipoles and of their characteristics have not been reported yet. Here we present a two-dimensional microfluidic quadrupole and a theoretical analysis consistent with the experimental observations. The microfluidic quadrupole was formed by simultaneously injecting and aspirating fluids from two pairs of opposing apertures in a narrow gap formed between a microfluidic probe and a substrate. A stagnation point was formed at the centre of the microfluidic quadrupole, and its position could be rapidly adjusted hydrodynamically. Following the injection of a solute through one of the poles, a stationary, tunable, and movable-that is, 'floating'-concentration gradient was formed at the stagnation point. Our results lay the foundation for future combined experimental and theoretical exploration of microfluidic planar multipoles including convective-diffusive phenomena.
authors: Biomedical Engineering Department, McGill University, Montréal, Quebec, Canada.
authors: Mohammad A
authors: MA
authors: Qasaimeh
authors: Thomas
authors: T
authors: Gervais
authors: David
authors: D
authors: Juncker
mesh_terms: D044085:Microfluidics