Effect of Stabilizing Particle Size on the Structure and Properties of Liquid Marbles

Abstract

A liquid marble (LM) describes a liquid droplet that is wrapped by nonwetting micro-or nanoparticles and therefore obtains characteristics of a solid powder particle. Here, we investigate the effect of the stabilizing particle size on the resulting structure and properties of the LM. We synthesize a series of polystyrene particles with ultrathin coatings of heptadecafluorooctanesulfonic acid-doped polypyrrole with diameters ranging between 1 and 1000 μm by an aqueous chemical oxidative seeded polymerization of pyrrole. The methodology produced a set of hydrophobic particles with similar surface characteristics to allow the formation of LMs and to probe size effects in the LM formation and stabilization efficiency. We found that particles with a size above 20 μm adsorb as a particle monolayer to the surface of the LM, while smaller particles are adsorbed as ill-defined, multilayered aggregates. These results indicate that the balance between particle−particle interaction and gravity is an important parameter to control the surface structure of the LMs. The assembly behavior and size of the particles also correlated with the mechanical integrity of the LM against fall impact. The mechanical resistance was affected by the gap distance between the inner liquid of the LM and supporting substrate, the capillary forces acting between the particles at the LM surface, and the potential energy that depended on the particle size. Last, we demonstrate that the broadband light-absorbing properties of the polypyrrole shell also allow manipulating the evaporation rate of the inner liquid.

Synthesis of dioctyl sulfosuccinate‐doped polypyrrole grains by aqueous chemical oxidative polymerization and their use as light‐responsive liquid marble stabilizer

“…Due to its low luminescence efficiency, PPy materials exhibit NIR light‐to‐heat photothermal property 61–65 . The UV–visible‐NIR spectra measured for the PPy‐BEH grains synthesized at Py/BEHSS molar ratios of 3/2, 3/1, 3/0.5, and 3/0.25 were similar to those reported for PPy materials 66 (Figure 6b) with an absorption band in NIR region.…”

Boxes fabricated from plate-stabilized liquid marbles

“…These results indicated that the stability of the LMs against drying increased with the degree of overlap of the plates as the mechanical stability of the LMs increases with an increase of the degrees of steric hindrance and interlocking among the plates. The stability against impact was correlated with the mechanical integrity of the LMs estimated based on the minimum potential energy above which their shapes were destroyed (Em) utilizing a customized drop stability evaluation apparatus 38,46,47 (Table S1, Figure S7). The potential energy (E) was calculated based on the equation 1.…”

“…In all plate systems, polyhedral LMs were formed and an increase of water volume, allowing a larger number of plates to adsorb onto the droplet, increased sphericity. The LMs were stabilized with plate monolayers rather than multilayers, indicating the gravitational force outcompeted plateplate interactions and thus removed plates not in direct contact with the liquid 38 . Due to the gravity effect, the LM shape started to deviate largely from (near)sphere to oblate at and above 50 µL (Note that the capillary length of water is 2.7 mm.…”

“…The LMs were stabilized with plate monolayers rather than multilayers, indicating that the gravitational force outcompeted plate–plate interactions and thus removed plates not in direct contact with the liquid. 38 Due to the gravity effect, the LM shape started to deviate largely from (near) spherical to oblate at and above 50 μL (note that the capillary length of water is 2.7 mm).…”

“…The stability against impact was correlated with the mechanical integrity of the LMs estimated based on the minimum potential energy above which their shapes were destroyed ( E m ) utilizing a customized drop stability evaluation apparatus 38,46,47 (Table S1 and Fig. S7, ESI † ).…”