  Dissipative Particle Dynamics (DPD) is becoming a popular particle based
method to study flow through microchannels due to the ease with which the
presence of biological cells or DNA chains can be modeled. Many Lab-On-Chip
(LOC) devices require the ability to manipulate the transport of cells or DNA
chains in the fluid flow. Microchannel surfaces coated with combinations of
hydrophilic and hydrophobic materials have been found useful for this purpose.
In this work, we have numerically studied the hydrodynamics of a steady
nonuniform developing flow between two infinite parallel plates with
hydrophilic and hydrophobic surfaces using DPD for the first time. The
hydrophobic and hydrophilic surfaces were modeled using partial-slip and
no-slip boundary conditions respectively in the simulations. We also propose a
new method to model the inflow and outflow boundaries for the DPD simulations.
The simulation results of the developing flow match analytical solutions from
continuum theory for no-slip and partial-slip surfaces to good accord.
  The entrance region constitutes a considerable fraction of the channel length
in miniaturized devices. Thus it is desirable for the length of the developing
region to be short as most microfluidic devices such as cell or DNA separators
and mixers are designed for the developed flow field. We studied the effect of
a hydrophilic strip near the inlet of a microchannel on the effective
developing length. We find that the presence of the hydrophobic strip
significantly reduces the developing length.

Fluid Dynamics