Title: Modelling the evaporation of nanoparticle suspensions from heterogeneous surfaces,
Abstract: We present a Monte Carlo (MC) grid-based model for the drying of drops of a
nanoparticle suspension upon a heterogeneous surface. The model consists of a
generalised lattice-gas in which the interaction parameters in the Hamiltonian
can be varied to model different properties of the materials involved. We show
how to choose correctly the interactions, to minimise the effects of the
underlying grid so that hemispherical droplets form. We also include the
effects of surface roughness to examine the effects of contact-line pinning on
the dynamics. When there is a `lid' above the system, which prevents
evaporation, equilibrium drops form on the surface, which we use to determine
the contact angle and how it varies as the parameters of the model are changed.
This enables us to relate the interaction parameters to the materials used in
applications. The model has also been applied to drying on heterogeneous
surfaces, in particular to the case where the suspension is deposited on a
surface consisting of a pair of hydrophilic conducting metal surfaces that are
either side of a band of hydrophobic insulating polymer. This situation occurs
when using inkjet printing to manufacture electrical connections between the
metallic parts of the surface. The process is not always without problems,
since the liquid can dewet from the hydrophobic part of the surface, breaking
the bridge before the drying process is complete. The MC model reproduces the
observed dewetting, allowing the parameters to be varied so that the conditions
for the best connection can be established. We show that if the hydrophobic
portion of the surface is located at a step below the height of the
neighbouring metal, the chance of dewetting of the liquid during the drying
process is significantly reduced.