Transport phenomena across nanopores/nanochannels induced by surface wiggling

Transportation through nanopore/ nanochannel is omnipresent in biological systems such as aquaporins. It has its significance also in engineering applications like desalination of water. The efficiency of biological pores in terms of mass flux is substantially high compared to the artificial nanochannels, despite the considerable breakthroughs achieved in recent years to transport fluids at nanoscales. In these biological pores, shape agitation due to the thermal fluctuation primarily facilitates the transport, as shown by Noskov et al. Understanding the underlying flow dynamics through these fluctuating nanopore is not just a matter of curiosity. It allows the identification of critical elements for designing active artificial nanochannels.

Mass flux through a wiggling nanopore varies due to the complex interplay between the diffusive transport and the dynamic agitation of pore shape. The advection in the flow induced by the temporal evolution of the pore-wall increases diffusive transport by the Taylor-Aris mechanism. On the other hand, geometric irregularities can entrap fluid particles, resulting in an entropic barrier and thus producing a low mass flux, as discussed in detail by Reguera and Rubí. In a more recent study, Marbach et al. established a general framework to correlate diffusive transport and the dynamic spectrum of surface fluctuations, which not only regards the situations where structural fluctuations of the confining pore are induced by thermal noise but also takes into account the cases with active fluctuations induced by external excitation. The theory showed pertinence at different length and time scales ranging from nanopore transport to larger-scale configurations such as active contractions in fungal species that facilitate nutrient transport. This study opens up the possibility of identifying the decisive factors to tune transport across artificial nanochannels by external excitations in applications such as nanoscale pumping, filtration, osmosis, DNA sequencing.