Capillary filling is the key phenomenon in planar chromatography techniques such as paper chromatography and thin layer chromatography. While capillary filling in channels of micrometers scale are experimentally verified that obeys well to Washburn’s law, there is evident show that the speed of capillary filling in nanochannels is noticeable lower than described by Washburn’s formula. This paper describes a model for capillary filling phenomenon in nanochannel. Experiments on the filling of electrolytic and nonelectrolytic solutions in polymeric nanochannels were carried out. The filling processes were observed and recorded. Filling distances were measured, from which filling speeds were derived. Formation of air bubbles was also observed with some channel’s geometry. A mathematical model to calculate the electroviscous effect was established. This model shows that contribution of electroviscous effect in the reduction of filling speed is small. This result also agrees well with other previous theoretical works on the electroviscous effect. That means beside electroviscous effect, there are other phenomena that contribute in the reduction of capillary filling speed in nanochannel, such as air bubbles formation. Those phenomena need to be described qualitatively and quantitatively in order to understand more on the capillary filling in nanochannel.

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