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 “liquid marbles” were readily prepared by rolling water droplets on a powder bed of dried submicrometer-sized polystyrene latex particles carrying poly­[2-(diethylamino)­ethyl 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 air–water interface of the liquid marbles. The polymeric capsules with aqueous volumes of 250 μL 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, organic–inorganic composite capsules and colloidal crystal capsules were fabricated from liquid marbles containing aqueous SiO₂ dispersions

Microcapsules Fabricated from Liquid Marbles Stabilized with Latex Particles

Millimeter- and centimeter-sized “liquid marbles” were readily prepared by rolling water droplets on a powder bed of dried submicrometer-sized polystyrene latex particles carrying poly­[2-(diethylamino)­ethyl 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 air–water interface of the liquid marbles. The polymeric capsules with aqueous volumes of 250 μL 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, organic–inorganic composite capsules and colloidal crystal capsules were fabricated from liquid marbles containing aqueous SiO₂ 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

Image_1_pH-Responsive Particle-Liquid Aggregates—Electrostatic Formation Kinetics.PDF

<p>Liquid-particle aggregates were formed electrostatically using pH-responsive poly[2-(diethylamino)ethyl methacrylate] (PDEA)-coated polystyrene particles. This novel non-contact electrostatic method has been used to assess the particle stimulus-responsive wettability in detail. Video footage and fractal analysis were used in conjunction with a two-stage model to characterize the kinetics of transfer of particles to a water droplet surface, and internalization of particles by the droplet. While no stable liquid marbles were formed, metastable marbles were manufactured, whose duration of stability depended strongly on drop pH. Both transfer and internalization were markedly faster for droplets at low pH, where the particles were expected to be hydrophilic, than at high pH where they were expected to be hydrophobic. Increasing the driving electrical potential produced greater transfer and internalization times. Possible reasons for this are discussed.</p

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 poly­[2-(diethylamino)­ethyl 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 (PDEA–PS particles) were successfully synthesized in polymerization media with solubility parameters ranging between 22.3 (MPa)^1/2 and 26.0 (MPa)^1/2. The number-average particle diameters were finely controlled between 90 and 460 nm. The PDEA–PS 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 PDEA–PS particles served as an effective gas-responsive stabilizer for liquid marbles. The liquid marbles were stable in H₂O vapor for over 18 h, but disintegrated immediately (<2 s) upon exposure to HCl gas

Gas Bubbles Stabilized by Janus Particles with Varying Hydrophilic–Hydrophobic Surface Characteristics

Micrometer-sized polymer-grafted gold–silica (Au-SiO₂) 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-SiO₂ Janus particles exhibited monolayer adsorption at the air–water interface and could stabilize bubbles, preventing their coalescence for more than 1 month. The hydrophobic PS-grafted Au and hydrophilic SiO₂ surfaces were exposed to the air and water phases, respectively. Bare Au-SiO₂ and poly­(2-(per­fluoro­butyl)­ethyl meth­acrylate) (PPFBEM)-grafted Au-SiO₂ 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-SiO₂ Janus particles, PPFBEM-grafted Au-SiO₂ Janus particles, and SiO₂ particle systems because of the high adsorption energy of the PS-grafted particles at the air–water interface

Polypyrrole–Palladium 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 polypyrrole–palladium (PPy–Pd) nanocomposite by chemical oxidative polymerization of pyrrole using PdCl₂ as an oxidant in aqueous media. Good control over the targeted PPy–Pd nanocomposite loading is achieved for 5.2 μm diameter polystyrene (PS) particles, and PS particles of up to 84 μm diameter can also be efficiently coated with the PPy–Pd 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 PPy–Pd nanocomposite. The Fourier transform infrared (FT-IR) spectrum of the PS particles coated with the PPy–Pd nanocomposite overlayer is dominated by the underlying particle, since this is the major component (>96% by mass). Thermogravimetric and elemental analysis indicated that PPy–Pd 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 PPy–Pd nanocomposite loading. “Flattened ball” 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 PPy–Pd 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 poly­(methyl methacrylate) particles with diameters ranging between 10 and 19 μm have been also successfully coated with PPy–Pd 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 carbon–carbon 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 “supraball” 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 poly­[2-(diethylamino)­ethyl 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 “supraball” 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 poly­[2-(diethylamino)­ethyl 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