Study of Flow-Driven Translocation of Flexible Polymer Chains through Cylindrical Nanopores in Unentangled Semidilute Solutions

This work reports our effort in clarifying the effect of solution concentration (C) on polymer translocation in semidilute solutions. By studying the translocation behavior of mono- and polydisperse linear polystyrenes through 20 nm cylindrical nanopores in toluene, we have quantified the relation between the macroscopic critical flow rate (Q) and the reduced concentration (C/C*) in the range of 1.0 < C/C* < 16.0, that is, Q(c) approximate to (C/C*)(gamma) with gamma = -0.8 +/- 0.1, where C* is the overlap concentration. Moreover, the translocation behavior is confirmed to be chain length-independent in semidilute solution. Considering that the critical entanglement concentration (C-e) separating the entangled and unentangled regimes is around 15C* (Polymer Physics: New York, 2003; Chapter 8), our studied concentration range falls in the "unentangled" regime, and the measured vertical bar gamma vertical bar = 0.8 is much smaller than vertical bar gamma vertical bar = 3.75 predicted by Daoudi and Brochard for the entangled regime (Macromolecules. 1978, 11, 751). Further, we have revealed that the translocation mechanism for well-defined hyperbranched systems is still regulated by the property of individual chains because of the suppressed interchain interaction/interpenetration in the semidilute regime, which is different from the "blob" picture for linear system. Finally, a simple theoretical description based on unentangled dynamics model has been utilized to qualitatively interpret our experimental data. By correlating the relaxation time (tau(r)) of translocation dynamics with the higher order of relaxation modes in the unentangled regime, that is, tau(r) approximate to tau(chain)/p(2), where p is the mode index and tau(chain )is the longest relaxation time, we have found that p is concentration-dependent. This finding suggests that the translocation dynamics might be dominated by the fast relaxation dynamics of correlated translocating blobs, rather than the slow relaxation of the whole chain/network.