Continuous Microfluidic Particle Separation via Elasto-Inertial Pinched Flow Fractionation.

Many of the fluids encountered in chemical and biomedical applications exhibit non-Newtonian behavior. However, the majority of current particle separation methods have been demonstrated in Newtonian fluids only. This work presents an experimental study of continuous particle separation in viscoelastic solutions via a combined action of elastic and inertial lift forces, which we term elasto-inertial pinched flow fractionation (eiPFF). The parametric effects on eiPFF are systematically investigated in terms of dimensionless numbers. It is found that eiPFF offers much higher particle throughput and separation resolution than the traditional steric effects-based PFF. Moreover, eiPFF works most efficiently when the Reynolds number, Re, is of order 1 and hence fills perfectly into the gap of our recently proposed inertia-enhanced PFF (iPFF) technique (Anal. Chem. 2015, 87, 4560-4565) that favors Re of the order 10 or more. However, the particle separation via eiPFF does not increase monotonically with the elasticity number at higher polymer concentrations and is strongly affected by the aspect ratio of channel width to height, both of which have not been previously reported. More surprisingly, the elasto-inertial deflection of small particles can be even greater than that of large particles in a high-aspect-ratio channel for Re less than 1.