Label-free separation of particles by an intrinsic property can be implemented in microfluidic devices through either an externally imposed field or an inherent flow-induced force. Among the latter type of passive techniques, elastic or elasto-inertial lift-based particle separation in non-Newtonian fluids has received a rapidly growing interest in the past decade. However, current demonstrations of particle separation in non-Newtonian fluids have all taken place in viscoelastic polymer or biological solutions. We demonstrate for the first time a continuous sheath-free separation of polystyrene particles in the flow of weakly elastic xanthan gum (XG) solution through a simple straight rectangular microchannel. This separation is fundamentally different from that in the flow of viscoelastic solutions. We explain the observed particle migrations in XG solutions using the competition of a strong wall-directed (because of the strong shear thinning effect) and a small center-directed (because of the weak elasticity effect) lateral force induced by normal stresses in a Poiseuille flow.

通过固有性质的无标记的颗粒分离可以在微流体装置中通过外部施加的场或固有的流动感应力来实现。在后一种被动技术中，在过去的十年中，非牛顿流体中基于弹性或弹性惯性升力的颗粒分离受到了越来越多的关注。但是，当前在非牛顿流体中进行颗粒分离的演示都在粘弹性聚合物或生物溶液中进行。我们第一次展示了通过简单的直矩形微通道在弱弹性黄原胶（XG）溶液流中聚苯乙烯颗粒的连续无鞘分离。这种分离从根本上不同于粘弹性溶液的流动。