The mechanisms of droplet penetration into porous media are investigated in
etched porous networks. In particular, we investigate the role of pore mor
phology on the rate of penetration, surface and sub-surface spreading rates
, observed contact angle, and resultant spatial distribution of fluid withi
n the porous network. Experiments on a range of pore networks illustrate th
e critical role played by morphology and fluid properties in determining th
e physics of fluid penetration. A description of different local penetratio
n events, the calculation of the associated displacement pressures and the
time scale associated with different events is given. This description is i
n good agreement with the experimental observations of fluid penetration at
the pore scale. From an understanding of the physical mechanisms observed
at the local pore scale one can build a general, but realistic, macroscopic
model for fluid penetration into realistic complex porous substrates. We d
iscuss the development of comprehensive tools for understanding penetration
into large disordered networks of capillaries.