Apparent Slip Due to the Motion of Suspended Particles in Flows of Electrolyte Solutions

Abstract

We consider pressure-driven flows of electrolyte solutions in small channels or capillaries in which tracer particles are used to probe velocity profiles. Under the assumption that the double layer is thin compared to the channel dimensions, we show that the flow-induced streaming electric field can create an apparent slip velocity for the motion of the particles, even if the flow velocity still satisfies the no-slip boundary condition. In this case, tracking of particle would lead to the wrong conclusion that the no-slip boundary condition is violated. We evaluate the apparent slip length, compare with experiments, and discuss the implications of these results.

Microfluidics: The No-Slip Boundary Condition

“…If the particles are charged, their velocity will also include an electrophoretic component in response to the flow-induced potential difference; moreover, if they are sufficiently charged, this velocity will be able to overcome the electro-osmotic back-flow in the bulk and the particles will move faster than the local liquid, leading to an apparent slip length. If we consider the case of a pressure driven flow between two parallel plates separated by a distance 2h, the resulting apparent slip length is given by [99] λ h ∼ ζ w (qζ p − ζ w )(ǫ r ǫ 0 ) 2 2σ e µh 2 + (ǫ r ǫ 0 ζ w ) 2 κh ,…”

The unique properties of the solid-like confined liquid films: A large scale molecular dynamics simulation approach

“…1. Possible influencing factors of the boundary slip: the wettability of the solid surface [32] , surface roughness [33] , the nanoscale vapor bubbles generated at the liquid-solid interface [34] , shear rate [35] , the electric double layer [36] , the shape and the arrangement of the liquid molecules [37] , variation of viscosity near the solid walls [38] .…”

“…The mechanism of the slip at the liquid-solid interface and between the layers of the confined liquid is of particular importance for the understanding of the shear response of the confined ultrathin films. The boundary slip is dependent on various factors, such as the wettability of the solid surface [32] , surface roughness [33] , the nanoscale vapor bubbles generated at the liquid-solid interface [34] , shear rate [35] , the electric double layer [36] , the shape and the arrangement of the liquid molecules [37] , variation of viscosity near the solid walls [38] , as summarized in Fig.1. For the slip of the confined liquid, Jabbarzadeh et al used a united atoms model in MD simulations to study the influence of wall properties on the slip between hexadecane film and the walls [39,40] .…”

Direct measurement of slip length in electrolyte solutions

“…водных растворов в сдвиговом пото-ке на гидрофильной и гидрофобной поверхностях. Однако, некоторые вопросы, в частности, о влиянии электростатических и/или электрокинетических сил на частицы -трейсеры, приводящем к ложному обнару-жению проскальзывания, остались открытыми [12,13]. В данной небольшой работе, представлены измерения длины проскальзывания ионных водных растворов, с использованием ВПВО, а также их сравнение с резуль-татами Хуанга (Huang) и др.…”

“…Электрокинетические эффекты [13] и электро-статическое отталкивание [12] между частицами -трейсерами и стеклянной поверхностью могут являться источниками, вызывающими кажущееся проскальзывание и влияющими на точность измере-ния скорости проскальзывания. Их влияние, однако, как ожидается, уменьшится с увеличением ионной силы испытуемых жидкостей.…”