posted on 2022-02-17, 16:34authored byGazendra Shakya, Apresio K. Fajrial, Xiaoyun Ding, Mark A. Borden
Vaporizable
hydrocarbon-in-fluorocarbon endoskeletal droplets are
a unique category of phase-change emulsions with interesting physical
and thermodynamic features. Here, we show microfluidic fabrication
of various morphologies, such as solid-in-liquid, liquid-in-solid,
and Janus-type, of complex solid n-C20H42 or n-C21H44 and liquid n-C5F12 droplets.
Furthermore, we investigated the vaporization behavior of these endoskeletal
droplets, focusing on the effects of heat treatment and core size.
Comparison of vaporization and differential scanning calorimetry results
indicated that vaporization occurs prior to melting of the bulk hydrocarbon
phase for C20H42/C5F10 droplets and near the rotator phase for C21H44/C5F10 droplets. We found that heat treatment
of the droplets increased the fraction of droplets that vaporized
and also increased the vaporization temperature of the droplets, although
the effect was temporary. Furthermore, we found that changing the
relative size of the solid hydrocarbon core compared to the surrounding
liquid shell increased the vaporization temperature and the vaporizing
fraction. Taken together, these data support the hypothesis that surface
melting behavior exhibited by the linear alkane may trigger the fluorocarbon
vaporization event. These results may aid in the understanding of
the interfacial thermodynamics and transport and the engineering of
novel vaporizable endoskeletal droplets for biomedical imaging and
other applications.