(340d) Electrophoretic Mobility of Nanoparticles Confined in Nanochannels

    We investigate the mobility of a charged nanoparticle confined in a nanochannel driven by a weak electric field. Classic models for electrophoretic mobility are valid only in the linear regime of small particle zeta potential, and for an unbounded fluid domain. However, these models fail to predict electrophoretic mobility estimated from experiments using 50 nm diameter spherical particles in a 100 nm nanochannel.

    We adopt asymptotically-expanded formulations and solve the fully-coupled equations on a 3D finite element domain to investigate such issues. Factors affecting particle mobility include electrolyte concentration, channel size, and zeta potentials on both the particle surface and channel walls. We find that nanochannel confinement combined with overlap of the double layers greatly affect the nanoparticle mobility. When the channel size is decreased from 2.5 um to 100 nm, the mobility is reduced by up to 20%. It also shows a possibility to use nanochannles to separate particles with the same zeta potential but different sizes. Finally, we propose a method to estimate corrected zeta potentials of the particle and walls from the observed mobility of a particle in both microchannels and nanochannels.

    In addition, rotation is important when rod-shape particles are considered. We investigate the motion of a 2 nm diameter and 3.4 nm high rod in a 100 nm nanochannel in a 2D domain. Different initial positions and orientations are considered to observe the confinement effect. It shows the particle would be confined at the center of the channel and aligned with the applied electric field when double layers are thick (> 9 nm).