ABSTRACT
Imagine a polyelectrolyte molecule of contour length ∼6μm and radius of gyration ∼500 nm having to find a tiny hole of radius ∼2 nm embedded in a wall that is essentially of infinite dimensions. This apparently daunting task of placing one end of the polymer at the pore entrance is the necessary first step for polymer translocation across a nanopore to occur. The same mechanisms discussed in the last chapter for the transport of small ions through pores, namely the diffusion, drift, and barriers, are operative for the transport of polyelectrolytes as well. The significant difference now is that the chain connectivity and the counterions of the polymer substantially modify these contributing factors. In addition, the electroosmotic flow (EOF) generated by charge-bearing pores in the presence of an electric field can lead to dramatic changes in the way the polymer is captured by the pore. There have been many experiments on the capture rate of the polymer by a nanopore, in terms of its dependence on the chain length, polymer concentration, salt concentration, and the strength of the applied voltage difference. We shall discuss the experimental findings in light of the various contributions arising from the diffusion, drift, barriers, and EOF, by assembling the various essential conceptual elements already described in the previous chapters. In the present chapter, we focus on the steady-state capture rate of the center-of-mass of the polymer and relegate the details of threading of the polymer through the pore to the next chapter.
