Locomotion of a Nonaqueous Liquid Marble Induced by Near-Infrared-Light Irradiation

Abstract

Micrometer-sized hydrophobic polyaniline (PANI) grains were synthesized via an aqueous chemical oxidative polymerization protocol in the presence of dopant carrying perfluoroalkyl or alkyl groups. The critical surface tensions of the PANIs synthesized in the presence of heptadecafluorooctanesulfonic acid and sodium dodecyl sulfate dopants were lower than that of PANI synthesized in the absence of dopant, indicating the presence of hydrophobic dopant on the grain surfaces. The PANI grains could adsorb to air–liquid interfaces, and aqueous and nonaqueous liquid marbles (LMs) were successfully fabricated using liquids with surface tensions ranging between 72.8 and 42.9 mN/m. Thermography studies confirmed that the surface temperature of the LMs increased by near-infrared light irradiation thanks to the photothermal property of the PANI, and the maximum temperatures measured for nonaqueous LMs were higher than that measured for aqueous LM. We demonstrated that transport of the LMs on a planar water surface can be achieved via Marangoni flow generated by the near-infrared light-induced temperature gradient. Numerical analyses indicated that the LMs containing liquids with lower specific heat and thermal conductivity and higher density showed longer path length per one light irradiation shot and longer decay time. This is because generated heat could efficiently transfer from the LMs to the water surface and larger inertial force could work on the LMs. The LMs could also move over the solid substrate thanks to their near-spherical shapes. Furthermore, it was also demonstrated that the inner liquids of the LMs could be released on site by an external stimulus.

Controllable Positive/Negative Phototaxis of Millimeter-Sized Objects with Sensing Function

“…This is probably because both LMs have the same shape and mass, and there is no significant difference in the viscous resistance from the water surface. The tetrahedral LMs showed shorter decay times compared with the LMs stabilized with conjugated polymer gains (0.68–1.18 s), which should be because an inertial force works weaker on the lighter tetrahedral LMs, as indicated by eq , (8 and 15 μL water droplets were used to prepare the tetrahedral LMs, and the LMs were stabilized with the conjugated polymer grains). Here, ζ is the drag coefficient and m is the mass of the LM. Friction force working on the LM during motions should also affect the decay time.…”

“…The LMs can move easily on the water surface and can conveniently transport inner encapsulated materials and solid particles/grains adsorbed to the LM surfaces. Recently, we demonstrated remote motion control of the LMs stabilized with conjugated polymer grains as a stabilizer by light irradiation. ,− , The conjugated polymer grains worked as a light-to-heat photothermal transducer as well as an LM stabilizer, and the LMs could move on the planar water surface based on light-induced Marangoni flow generated by light irradiation. Here, the motion of LMs could be induced only in a negative phototactic manner, because the light could not penetrate through the LMs due to light scattering and absorption by the grains on the LM surfaces, and light irradiation was limited only on one side of the LMs.…”

Synthesis of Polypyrrole and Its Derivatives as a Liquid Marble Stabilizer via a Solvent-Free Chemical Oxidative Polymerization Protocol

“…The decay time of the locomotion was 1.10 ± 0.25 s ( Figure S9 ), which was also similar to those determined for the LMs previously reported. 30 , 39 , 52 , 73 , 75 , 76 …”

“…Recently, research on stimuli-responsive LMs, whose stability, structure, shape, and motion can be controlled/tuned by external stimuli, gains increasing interest . Based on their stimuli-responsive characters, potential applications of the LMs have been proposed in areas such as sensors, miniature reactors, microfluidics, pressure-sensitive adhesives, and material delivery carriers. − Recently, we succeeded in synthesis of hydrophobic PPy, PANI, and PEDOT grains by aqueous chemical oxidative polymerizations using perfluoroalkyl dopants and demonstrated that the dried grain powders can work as an LM stabilizer with a light-to-heat photothermal property. − Additionally, the remote locomotion control of LMs on a planar air–water surface was realized by light-induced Marangoni propulsion: anisotropic heat gradient was generated around the LM floating on the water surface by the local NIR-laser irradiation of the LMs. Here, the perfluoroalkyl dopants, which have been used as a hydrophobizing agent for PPy, PANI, and PEDOT, show low biodegradability and are known to be a persistent organic pollutant. , Therefore, development of perfluoroalkyl dopant-free light-responsive LM stabilizers is crucial.…”

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

“…Recently, we successfully synthesized hydrophobic conjugated polymer grains, such as polypyrrole (PPy), 31,32 polyaniline (PANI) 33,34 and poly(3,4‐ethylenedioxythiophene) (PEDOT), 35 by one‐step aqueous chemical oxidation polymerization in the presence of heptadecafluorooctanesulfonic acid, a perfluoroalkyl dopant. Furthermore, we confirmed that these conjugated polymer grains could adsorb to air‐water surface to stabilize LMs.…”