posted on 2021-02-01, 13:40authored byMohammad
J. Inanlu, Behrooz Shojaan, Jafar Farhadi, Vahid Bazargan
Controlling
and suppressing the so-called “coffee-ring effect”
(CRE) is an issue of cardinal importance and intense interest in many
industries and scientific fields. Here, the combined effect of the
particle and surfactant concentration on the CRE is investigated by
gradually adding Triton X-100 surfactant to colloidal suspensions
of SiO2 nanoparticles in ethanol for various particle concentrations.
First, the effect of particle concentration on the contact line dynamics
during the evaporation of a sessile droplet is investigated. It is
shown that increasing the particle concentration leads to an increase
in pinning time and ring width, whereas the droplet’s initial
and dynamic contact angle remains unchanged. Afterward, the effect
of different concentrations of surfactant is studied for different
particle concentrations. It is concluded that the surfactant concentration
at which the CRE is suppressed is dependent on the initial particle
concentration of the colloid, and it increases as the particle concentration
increases. Furthermore, as adding surfactant with a concentration
lower than this critical concentration results in an unsuppressed
CRE, it is shown that surpassing this concentration will result in
a depletion of particles in the contact line. Moreover, it is demonstrated
that this critical surfactant concentration has no significant effect
on the droplet’s geometry and the total evaporation time.