(209a) Stochastic and Deterministic Vector Separation of Suspended Particles In 1D Periodic Free-Energy Landscapes

Minituarized systems for chemical and biological analysis have shown great promise to replace their existing counter parts and have open the door for exciting new technologies exploiting phenomena that dominate at the micro and nanoscale. Vector chromatography (VC), in which the different species of a sample migrate in different average directions in a planar microfluidic device, is very promising because it allows great resolution, continuous fractionation and high throughputs. The selective displacement in VC is caused by a force applied at an angle with respect to the direction of the driving field. A number of promising techniques to induce the deflecting force have been previously studied, involving driving the particles through periodic systems that are invariant in one of the directions of the separation plane. Examples include the fractionation through periodic dielectrophoretic and magnetic fields, and periodic entropic traps. In this talk, we present a unified description of these cases heretofore presented independently. Under conditions of fast equilibration in the direction perpendicular to the separation plane, the deflecting force can be identified with a thermodynamic force resulting from gradients in the free-energy of the particles, and thus encompassing the enthalpic and entropic cases. In general, the parameters governing the migration angle of a given species are the ratio between driving and deflecting forces, and the relative magnitude of the potential of mean force and of the driving force with respect to thermal energy. For cases in which the potential of mean-force is given by a constant step-wise function, the deflection angle is governed by a partition ratio and the Peclet number. We will present results of model potentials and study the effect of the relevant parameters and their associated regimes. Experimental results agree well with the theory and confirm the model predictions.