  The translocation of a polymer through a pore in a membrane separating fluids
of different viscosities is studied via several computational approaches.
Starting with the polymer halfway, we find that as a viscosity difference
across the pore is introduced, translocation will predominately occur towards
one side of the membrane. These results suggest an intrinsic pumping mechanism
for translocation across cell walls which could arise whenever the fluid across
the membrane is inhomogeneous. Somewhat surprisingly, the sign of the preferred
direction of translocation is found to be strongly dependent on the simulation
algorithm: for Langevin Dynamics (LD) simulations, a bias towards the low
viscosity side is found while for Brownian Dynamics (BD), a bias towards the
high viscosity is found. Examining the translocation dynamics in detail across
a wide range of viscosity gradients and developing a simple force model to
estimate the magnitude of the bias, the LD results are demonstrated to be more
physically realistic. The LD results are also compared to those generated from
a simple, one dimensional random walk model of translocation to investigate the
role of the internal degrees of freedom of the polymer and the entropic
barrier. To conclude, the scaling of the results across different polymer
lengths demonstrates the saturation of the preferential direction with polymer
length and the non-trivial location of the maximum in the exponent
corresponding to the scaling of the translocation time with polymer length.
