Near-infrared (NIR) light irradiation induced the transformation of polypyrrole (PPy) to nitrogen-containing carbon (NCC) material due to its light-toheat photothermal property. The temperature of the PPy increased over 700 °C within a few seconds by the NIR laser irradiation, and elemental microanalysis confirmed the decreases of hydrogen and chloride contents and increases of carbon and nitrogen contents. Monodispersed polystyrene (PS)-core/PPy shell particles (PS/PPy particles) synthesized by aqueous chemical oxidative seeded polymerization were utilized as a precursor toward monodispersed NCC capsules. When the NIR laser was irradiated to the PS/PPy particles, the temperature rose to approximately 300 °C and smoke was generated, indicating that the PS component forming the core was thermally decomposed and vaporized. Scanning electron microscopy studies revealed the successful formation of spherical and highly monodispersed capsules, and Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy studies confirmed the capsules consisted of NCC materials. Furthermore, sunlight was also demonstrated to work as a light source to fabricate NCC capsules. The size and thickness of the capsules can be controlled between 1 and 80 μm and 146 and 231 nm, respectively, by tuning the size of the original PS/PPy particles and PPy shell thickness.
In
this study, we report on the fabrication
of photo/thermo
dual
stimulus-responsive liquid marbles (LMs) that can be disrupted by
light irradiation and/or heating. To stabilize the LMs, we synthesized
micrometer-sized stearic acid (SA) particles coated with overlayers
of polypyrrole (PPy) by aqueous chemical oxidative seeded dispersion
polymerization. The SA/PPy core–shell particles could adsorb
at the air–water interface to stabilize LMs by rolling water
droplets on the particle powder bed. The presence of SA, known as
a phase-change material, which undergoes a transition from solid to
liquid by heating, and PPy, which can transduce light to heat, gives
rise to the photo and thermo dual stimulus-responsive characters of
the LMs. The disruption of the LMs could be induced in a cascade manner:
light irradiation on the LM induced a temperature increase, followed
by melting of the SA component on the LM surface, leading to its disruption
and release of the inner water. The disruption time is linked to the
PPy loading and light irradiation power, and it can be tuned from
quasi-instantaneous to a few tens of seconds. The melting of SA due
to a light-induced phase change from the solid to liquid state is
a new mechanism to trigger the disruption of LMs. We finally demonstrated
two applications of the LMs as a light-responsive microreactor and
a sensor.
Polyhedral liquid marbles were fabricated using hydrophobic polymer plates in the shape of circle, heart and star as a stabilizer and water as an inner liquid phase. Boxes could be...
Phototaxis,
which is the directional motion toward or away from
light, is common in nature and inspires development of artificial
light-steered active objects. Most of the light-steered objects developed
so far exhibit either positive or negative phototaxis, and there are
few examples of research on objects that exhibit both positive and
negative phototaxis. Herein, small objects showing both positive and
negative phototaxis on the water surface upon near-infrared (NIR)
light irradiation, with the direction controlled by the position of
light irradiation, are reported. The millimeter-sized tetrahedral
liquid marble containing gelled water coated by one polymer plate
with light-to-heat photothermal characteristic, which adsorbs onto
the bottom of the liquid marble, and three polymer plates with highly
transparent characteristic, which adsorb onto the upper part of the
liquid marble, is utilized as a model small object. Light irradiation
on the front side of the object induces negative phototaxis and that
on the other side induces positive phototaxis, and the motion can
be controlled to 360° arbitrary direction by precise control
of the light irradiation position. Thermographic studies confirm that
the motions are realized through Marangoni flow generated around the
liquid marble, which is induced by position-selective NIR light irradiation.
The object can move centimeter distances, and numerical analysis indicates
that average velocity and acceleration are approximately 12 mm/s and
71 mm/s2, respectively, which are independent of the direction
of motions. The generated force is estimated to be approximately 0.4
μN based on Newton’s equation. Furthermore, functional
cargo can be loaded into the inner phase of the small objects, which
can be delivered and released on demand and endows them with environmental
sensing ability.
Poly(3,4-ethylenedioxythiophene) (PEDOT) grains were synthesized by solvent-free chemical oxidative polymerization in one-step and one-pot manner. The resulting PEDOT grains had atypical shapes with a volume-average diameter of 57 ± 45 µm and showed an electrical conductivity of 1.9 × 10−3 S cm−1. Furthermore, it was clarified that the PEDOT grains showed light-to-heat photothermal property.
Polypyrrole grains are synthesized by aqueous chemical oxidative polymerization using ferric chloride as an oxidant in the presence of bis(2‐ethylhexyl) sulfosuccinate sodium salt as both a dopant and a hydrophobizing agent. The resulting grain products are characterized in terms of their size, morphology, surface and bulk chemical compositions, hydrophilicity‐hydrophobicity balance, (photo) thermal property, and electrical conductivity. Scanning electron microscopy studies indicate that the grains are aggregates of atypical primary grains with submicrometer size. Elemental microanalysis and thermogravimetric analysis confirm that the polypyrrole is preferably doped with dioctyl sulfosuccinate compared with chloride ion, and dioctyl sulfosuccinate/chloride ion dopant ratio increases with an increase of bis(2‐ethylhexyl) sulfosuccinate sodium salt concentration in the polymerization systems. The grains show near‐infrared light‐to‐heat photothermal property, which is confirmed by thermography. The data obtained through X‐ray photoelectron spectroscopy indicate the presence of dioctyl sulfosuccinate dopants on the surface of the grains, and therefore the dried polypyrrole grains show hydrophobic character. The dried grains can work as a light‐responsive liquid marble (LM) stabilizer. Motions of the LM can be driven by near‐infrared laser irradiation‐induced Marangoni flow on planar air‐water surface. The release of internal liquid can be achieved by controlled disruption of the LM via external stimulus application.
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