distance between particle clusters resulting from the demixing process that occurs already in the
bulk liquid and is not related to the front instability at all. Note that one ﬁnds a similar sequence
of regimes (i) to (iv) when increasing the particle-particle interaction strengths for ﬁxed εnl (see
Ref. [41]) for further details.
1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2
εnl
0
5
10
15
20
25<f>
(i)(ii)(iii)(iv)
FIG. 3: (Colour online) Dependence of the mean ﬁnger number left behind by the unstable dewetting
front on the particle-liquid interaction strength εnl. The regions marked (i) to (iv) are discussed in the
main text. The insets display typical snapshots obtained in the four different regions. Particles are black,
liquid is grey (green online) and the empty substrate is white. The remaining parameters are kT = 0 .2,
M = 20, µ = −2.2, ρav
n = 0.1, ϵnn = 2.0, domain size 1200 ×1200. For the insets, from left to right,
ϵnl = 1.2,1.4,1.45,1.8.
We note also that the ﬁngering process may be viewed as self-optimising the front motion – i.e.
the front keeps its average velocity constant by expelling particles into the ﬁngers. A similar effect
exists for dewetting polymer ﬁlms [18], where liquid is expelled from the growing moving rim
which collects the dewetted polymer. There, the surplus liquid is left on the surface as a droplet
pattern.
The kinetic Monte Carlo model is a very useful tool that helps one to understand the pattern
formation in drying nanoparticle suspensions. One has, however, to keep in mind the restrictions
13