17 research outputs found
Formation of Pickering Emulsions Stabilized via Interaction between Nanoparticles Dispersed in Aqueous Phase and Polymer End Groups Dissolved in Oil Phase
The influence of end groups of a polymer dissolved in
an oil phase
on the formation of a Pickering-type hydroxyapatite (HAp) nanoparticle-stabilized
emulsion and on the morphology of HAp nanoparticle-coated microspheres
prepared by evaporating solvent from the emulsion was investigated.
Polystyrene (PS) molecules with varying end groups and molecular weights
were used as model polymers. Although HAp nanoparticles alone could
not function as a particulate emulsifier for stabilizing dichloromethane
(oil) droplets, oil droplets could be stabilized with the aid of carboxyl
end groups of the polymers dissolved in the oil phase. Lower-molecular-weight
PS molecules containing carboxyl end groups formed small droplets
and deflated microspheres, due to the higher concentration of carboxyl
groups on the droplet/microsphere surface and hence stronger adsorption
of the nanoparticles at the water/oil interface. In addition, Pickering-type
suspension polymerization of styrene droplets stabilized by PS molecules
containing carboxyl end groups successfully led to the formation of
spherical HAp-coated microspheres
Microcapsules Fabricated from Liquid Marbles Stabilized with Latex Particles
Millimeter-
and centimeter-sized âliquid marblesâ
were readily prepared by rolling water droplets on a powder bed of
dried submicrometer-sized polystyrene latex particles carrying polyÂ[2-(diethylamino)Âethyl
methacrylate] hairs (PDEA-PS). Scanning electron microscopy studies indicated that flocs of the
PDEA-PS particles were adsorbed at the surface of these water droplets,
leading to stable spherical liquid marbles. The liquid marbles were
deformed as a result of water evaporation to adopt a deflated spherical
geometry, and the rate of water evaporation decreased with increasing
atmospheric relative humidity. Conversely, liquid marbles formed using
saturated aqueous LiCl solution led to atmospheric water absorption
by the liquid marbles and a consequent mass increase. The liquid marbles
can be transformed into polymeric capsules containing water by exposure
to solvent vapor: the PDEA-PS particles were plasticized with the
solvent vapor to form a polymer film at the airâwater interface
of the liquid marbles. The polymeric capsules with aqueous volumes
of 250 ÎŒL or less kept their oblate ellipsoid/near spherical
shape even after complete water evaporation, which confirmed that
a rigid polymeric capsule was successfully formed. Both the rate of
water evaporation from the pure water liquid marbles and the rate
of water adsorption into the aqueous LiCl liquid marbles were reduced
with an increase of solvent vapor treatment time. This suggests that
the number and size of pores within the polymer particles/flocs on
the liquid marble surface decreased due to film formation during exposure
to organic solvent vapor. In addition, organicâinorganic composite
capsules and colloidal crystal capsules were fabricated from liquid
marbles containing aqueous SiO<sub>2</sub> dispersions
Microcapsules Fabricated from Liquid Marbles Stabilized with Latex Particles
Millimeter-
and centimeter-sized âliquid marblesâ
were readily prepared by rolling water droplets on a powder bed of
dried submicrometer-sized polystyrene latex particles carrying polyÂ[2-(diethylamino)Âethyl
methacrylate] hairs (PDEA-PS). Scanning electron microscopy studies indicated that flocs of the
PDEA-PS particles were adsorbed at the surface of these water droplets,
leading to stable spherical liquid marbles. The liquid marbles were
deformed as a result of water evaporation to adopt a deflated spherical
geometry, and the rate of water evaporation decreased with increasing
atmospheric relative humidity. Conversely, liquid marbles formed using
saturated aqueous LiCl solution led to atmospheric water absorption
by the liquid marbles and a consequent mass increase. The liquid marbles
can be transformed into polymeric capsules containing water by exposure
to solvent vapor: the PDEA-PS particles were plasticized with the
solvent vapor to form a polymer film at the airâwater interface
of the liquid marbles. The polymeric capsules with aqueous volumes
of 250 ÎŒL or less kept their oblate ellipsoid/near spherical
shape even after complete water evaporation, which confirmed that
a rigid polymeric capsule was successfully formed. Both the rate of
water evaporation from the pure water liquid marbles and the rate
of water adsorption into the aqueous LiCl liquid marbles were reduced
with an increase of solvent vapor treatment time. This suggests that
the number and size of pores within the polymer particles/flocs on
the liquid marble surface decreased due to film formation during exposure
to organic solvent vapor. In addition, organicâinorganic composite
capsules and colloidal crystal capsules were fabricated from liquid
marbles containing aqueous SiO<sub>2</sub> dispersions
Transfer of Materials from Water to Solid Surfaces Using Liquid Marbles
Remotely controlling
the movement of small objects is desirable, especially for the transportation
and selection of materials. Transfer of objects between liquid and
solid surfaces and triggering their release would allow for development
of novel material transportation technology. Here, we describe the
remote transport of a material from a water film surface to a solid
surface using quasispherical liquid marbles (LMs). A light-induced
Marangoni flow or an air stream is used to propel the LMs on water.
As the LMs approach the rim of the water film, gravity forces them
to slide down the water rim and roll onto the solid surface. Through
this method, LMs can be efficiently moved on water and placed on a
solid surface. The materials encapsulated within LMs can be released
at a specific time by an external stimulus. We analyzed the velocity,
acceleration, and force of the LMs on the liquid and solid surfaces.
On water, the sliding friction due to the drag force resists the movement
of the LMs. On a solid surface, the rolling distance is affected by
the surface roughness of the LMs
Gas Bubbles Stabilized by Janus Particles with Varying HydrophilicâHydrophobic Surface Characteristics
Micrometer-sized
polymer-grafted goldâsilica (Au-SiO<sub>2</sub>) Janus particles
were fabricated by vacuum evaporation followed
by polymer grafting. The Janus particle diameter, diameter distribution,
morphology, surface chemistry, and water wettability were characterized
by optical microscopy, scanning electron microscopy, X-ray photoelectron
spectroscopy, and contact angle measurements. The optical microscopy
results showed that the polystyrene (PS)-grafted Au-SiO<sub>2</sub> Janus particles exhibited monolayer adsorption at the airâwater
interface and could stabilize bubbles, preventing their coalescence
for more than 1 month. The hydrophobic PS-grafted Au and hydrophilic
SiO<sub>2</sub> surfaces were exposed to the air and water phases,
respectively. Bare Au-SiO<sub>2</sub> and polyÂ(2-(perÂfluoroÂbutyl)Âethyl
methÂacrylate) (PPFBEM)-grafted Au-SiO<sub>2</sub> Janus particles
could also stabilize bubbles for up to 2 weeks. By contrast, bare
silica particles did not stabilize bubbles and were dispersed in water.
The bubbles that formed in the PS-grafted Janus particle system were
more stable than those formed in the bare Au-SiO<sub>2</sub> Janus
particles, PPFBEM-grafted Au-SiO<sub>2</sub> Janus particles, and
SiO<sub>2</sub> particle systems because of the high adsorption energy
of the PS-grafted particles at the airâwater interface
pH-Responsive Hairy Particles Synthesized by Dispersion Polymerization with a Macroinitiator as an Inistab and Their Use as a Gas-Sensitive Liquid Marble Stabilizer
We studied dispersion polymerization in detail using <i>well-defined</i> pH-responsive polyÂ[2-(diethylamino)Âethyl methacrylate]-
(PDEA-) based macroinitiators as an inistab (<i>ini</i>tiator
+ <i>stab</i>ilizer). Colloidally stable polystyrene (PS)
latex particles carrying pH-responsive PDEA hair (PDEAâPS particles)
were successfully synthesized in polymerization media with solubility
parameters ranging between 22.3 (MPa)<sup>1/2</sup> and 26.0 (MPa)<sup>1/2</sup>. The number-average particle diameters were finely controlled
between 90 and 460 nm. The PDEAâPS latex particles were dispersed
in acidic aqueous media in which the PDEA hair was protonated and
solvated, and were flocculated in basic aqueous media in which the
PDEA hair was deprotonated and precipitated. The dried PDEAâPS
particles served as an effective gas-responsive stabilizer for liquid
marbles. The liquid marbles were stable in H<sub>2</sub>O vapor for
over 18 h, but disintegrated immediately (<2 s) upon exposure to
HCl gas
PolypyrroleâPalladium Nanocomposite Coating of Micrometer-Sized Polymer Particles Toward a Recyclable Catalyst
A range of near-monodisperse, <i>multimicrometer-sized</i> polymer particles has been coated with ultrathin overlayers of polypyrroleâpalladium
(PPyâPd) nanocomposite by chemical oxidative polymerization
of pyrrole using PdCl<sub>2</sub> as an oxidant in aqueous media.
Good control over the targeted PPyâPd nanocomposite loading
is achieved for 5.2 ÎŒm diameter polystyrene (PS) particles,
and PS particles of up to 84 ÎŒm diameter can also be efficiently
coated with the PPyâPd nanocomposite. The seed polymer particles
and resulting composite particles were extensively characterized with
respect to particle size and size distribution, morphology, surface/bulk
chemical compositions, and conductivity. Laser diffraction studies
of dilute aqueous suspensions indicate that the polymer particles
disperse stably before and after nanocoating with the PPyâPd
nanocomposite. The Fourier transform infrared (FT-IR) spectrum of
the PS particles coated with the PPyâPd nanocomposite overlayer
is dominated by the underlying particle, since this is the major component
(>96% by mass). Thermogravimetric and elemental analysis indicated
that PPyâPd nanocomposite loadings were below 6 wt %. The conductivity
of pressed pellets prepared with the nanocomposite-coated particles
increased with a decrease of particle diameter because of higher PPyâPd
nanocomposite loading. âFlattened ballâ morphologies
were observed by scanning/transmission electron microscopy after extraction
of the PS component from the composite particles, which confirmed
a PS core and a PPyâPd nanocomposite shell morphology. X-ray
diffraction confirmed the production of elemental Pd and X-ray photoelectron
spectroscopy studies indicated the existence of elemental Pd on the
surface of the composite particles. Transmission electron microscopy
confirmed that nanometer-sized Pd particles were distributed in the
shell. Near-monodisperse polyÂ(methyl methacrylate) particles with
diameters ranging between 10 and 19 ÎŒm have been also successfully
coated with PPyâPd nanocomposite, and stable aqueous dispersions
were obtained. The nanocomposite particles functioned as an efficient
catalyst for the aerobic oxidative homocoupling reaction of 4-carboxyphenylboronic
acid in aqueous media for the formation of carbonâcarbon bonds.
The composite particles sediment in a short time
Controlling the Structure of Supraballs by pH-Responsive Particle Assembly
Supraballs
of various sizes and compositions can be fabricated
via drying of drops of aqueous colloidal dispersions on super-liquid-repellent
surfaces with no chemical waste and energy consumption. A âsupraballâ
is a particle composed of colloids. Many properties, such as mechanical
strength and porosity, are determined by the ordering of a colloidal
assembly. To tune such properties, a colloidal assembly needs to be
controlled when supraballs are formed during drying. Here, we introduce
a method to control a colloidal assembly of supraballs by adjusting
the dispersity of the colloids. Supraballs are fabricated on superamphiphobic
surfaces from colloidal aqueous dispersions of polystyrene microparticles
carrying pH-responsive polyÂ[2-(diethylamino)Âethyl methacrylate]. Drying
of dispersion drops at pH 3 on superamphiphobic surfaces leads to
the formation of spherical supraballs with densely packed colloids.
The pH 10 supraballs are more oblate and consist of more disordered
colloids than the pH 3 supraballs, caused by particle aggregates with
random sizes and shapes in the pH 10 dispersion. Thus, the shape,
crystallinity, porosity, and mechanical properties could be controlled
by pH, which allows broader uses of supraballs
Controlling the Structure of Supraballs by pH-Responsive Particle Assembly
Supraballs
of various sizes and compositions can be fabricated
via drying of drops of aqueous colloidal dispersions on super-liquid-repellent
surfaces with no chemical waste and energy consumption. A âsupraballâ
is a particle composed of colloids. Many properties, such as mechanical
strength and porosity, are determined by the ordering of a colloidal
assembly. To tune such properties, a colloidal assembly needs to be
controlled when supraballs are formed during drying. Here, we introduce
a method to control a colloidal assembly of supraballs by adjusting
the dispersity of the colloids. Supraballs are fabricated on superamphiphobic
surfaces from colloidal aqueous dispersions of polystyrene microparticles
carrying pH-responsive polyÂ[2-(diethylamino)Âethyl methacrylate]. Drying
of dispersion drops at pH 3 on superamphiphobic surfaces leads to
the formation of spherical supraballs with densely packed colloids.
The pH 10 supraballs are more oblate and consist of more disordered
colloids than the pH 3 supraballs, caused by particle aggregates with
random sizes and shapes in the pH 10 dispersion. Thus, the shape,
crystallinity, porosity, and mechanical properties could be controlled
by pH, which allows broader uses of supraballs
pH-Sensitive Adsorption Behavior of Polymer Particles at the AirâWater Interface
pH-Sensitive
adsorption of polymer particles bearing polyÂ[2-(dimethylamino)Âethyl
methacrylate] hairs at the airâwater interface was investigated
using a surface tensiometer, a LangmuirâBlodgett trough, and
an X-ray reflectometer. We clarified that the particles are adsorbed
at the interface at basic pH; by contrast, at acidic pH, only a small
number of particles are adsorbed, whereas the majority are dispersed
in the water phase. X-ray reflectometry analysis revealed that a particle
monolayer was formed at the airâwater interface, which was
packed densely under increasing surface pressure, as determined by
the electron density profile change. The contact angles of the particles
at the airâwater interface were estimated to be 29° and
34° at pH 3 and 10, respectively, by direct visualization of
the airâwater interface position of the particles using a polycyanoacrylate
trapping method