| Micro- and nano-particles are used in a wide range of applications in different industries including the pharmaceutical, medical, food, and energy. Their prominence has prompted scientific and technological advances that have lead to both, improved ways to process them more efficiently, as well as to the discovery and understanding of phenomena at small scales. Micro and nanofluidic systems for chemical and biological separation have opened the door for exciting new technologies that will be crucial components of integrated systems in lab-on-a-chip platforms. Particularly promising is vector separation (VC), in which different species in a sample migrate in different directions and can be continuously fractionated with high selectivity. In general, VC can be achieved by driving the particles in one direction and, at the same time, inducing selective transport in the perpendicular direction.;In this thesis, I will present two novel and versatile platforms that take advantage of the control on the geometry and chemistry provided by available fabrication techniques to induce this selective transport.;In the first chapter, I will demonstrate the separation capability of a microfluidic system in which gravity both drives the particles and, along with an array of parallel ramps patterned at the bottom surface of the device, creates a landscape of potential energy barriers. I will describe these results in terms of a unified description of VC in systems in which suspended Brownian particles are driven through 1-D energetic and entropic landscapes. In these systems, driving the particles at an slanted angle with respect to the periodic direction results in a deflection: the particles move uniformly in the invariant direction, but are retarded in the periodic direction as they overcome the energy or entropy barriers.;In the second chapter, I will present another mechanism that leads to VC in devices in which the bottom surface is patterned with slanted cavities instead of ramps. These cavities guide flow along them that induces the VC of suspended particles which size is comparable to the height of the ridges and that move in the vicinity of the patterned surface. Two regimes can be distinguished depending on the settling velocity of the particles compared to their average velocity across the cavities. When these velocities are similar, heavier particles settle deeper into the open cavities and exhibit larger lateral displacements induced by the flow along these cavities. On the other hand, if sedimentation is negligible, the flow advects smaller particles deeper into the cavities and, as a result, they deflect more than larger particles. I will present experiments separating particles based on size and density using these two techniques, and also demonstrate the separation of cells showing that different blood components can be deflected to a different extent. |
