Abstract
How to describe the ``electric double layer'' that is at the root of all electrokinetic phenomena such as electrophoresis and electro-osmosis? A new theoretical approach, introducing the concept of a surface potential trap and applying the constraint of global charge neutrality rigorously, answers this century-old question in the context of contemporary electrokinetics involving nanoscale systems and time-dependent electric fields.
Highlights
Electrokinetics (EK) is a classic subject that dates back nearly two centuries [1]
The consistency requirement leads to the charge-conserving Poisson-Boltzmann (CCPB) equation, which guarantees charge neutrality
(2) A crucial element of our model is the introduction of a surface potential trap that attributes an energy cost to the interfacial charge dissociation process
Summary
Electrokinetics (EK) is a classic subject that dates back nearly two centuries [1]. It involves the interaction of ions in the fluid with the solid surface, and their dynamics under an applied electric field tangential to the fluid-solid interface. The resulting treatment is not mathematically self-contained This can be a problem in treating nanoscale or time-varying electrokinetics, for example, since the interfacial charge layer would necessarily respond to the local fluid conditions, either as a function of time or as a function of separation between two charged surfaces, thereby requiring constant hands-on corrections for achieving charge neutrality. Experimental evidences, mainly obtained from atomic-force-microscope measurements, have indicated a variation of the surface charge density when the channel width decreases below the Debye length, which does not agree with the predictions resulting from either the CP or the CC boundary condition This discrepancy is generally attributed to the “charge regulation” phenomenon, denoting the fact that the interfacial charge layer must vary as a function of local environment. IX with a summary of the main points, and note the challenges ahead
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