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There is increasing interest in solid particle-stabilized soft dispersed systems, including bubbles/foams (a gas-in-liquid dispersed system) and liquid marbles (a liquid-in-gas dispersed system). The studies on these dispersed systems have mainly been conducted utilizing inorganic particles and research using polymer particles has recently gained attention. Synthetic colloidal polymer particles are attractive stabilizers, as their hydrophilic–hydrophobic character and surface chemistries can be designed and controlled on demand via polymerization with various functional monomers and post polymer reactions. The successful synthesis of polymer particles would inspire the construction of well-defined and functionalized particle-stabilized gas–liquid soft dispersed systems. In this review article, bubbles/foams and liquid marbles stabilized solely with stimulus-responsive polymer particles will be reviewed. The stabilities, structures, and motions of these dispersed systems can be controlled by external stimuli.

Polystyrene particle-stabilized Pickering-type paraffin droplets were successfully coated by polypyrrole overlayers by aqueous chemical oxidative polymerization of pyrrole, and the thickness of polypyrrole overlayer could be controlled simply by changing pyrrole concentration in the polymerization media. Remote motion control of the droplets was realized on a planar air–water surface by site-selective near-infrared light irradiation, due to light-to-heat photothermal property of the polypyrrole. Furthermore, motion control of the paraffin droplet was also possible using sunlight focused using a magnifying glass. A Marangoni flow induced by site-selective light irradiation of the droplet could work as a driving force to move the droplet on the air–water surface, and the direction and timing of irradiation could control those of the motion on demand. Path length, velocity, and decay time of the droplet motions became longer and larger with an increase of thickness of polypyrrole overlayer, which was confirmed by numerical analyses.

Polypyrrole, poly(N-methyl pyrrole) and poly(N-ethyl pyrrole) grains were synthesized by aqueous chemical oxidative polymerization in the presence of sodium dodecyl sulfate as both a dopant and a hydrophobizing agent. The resulting grain products were characterized in terms of their size, morphology, surface and bulk chemical compositions, hydrophilic–hydrophobic balance, (photo)thermal property, and conductivity. Scanning electron microscopy studies indicated that the grains were aggregates of atypical particles with submicrometer size. Elemental microanalysis and thermogravimetric analysis confirmed the production of dodecyl sulfate-doped polypyrrole, poly(N-methyl pyrrole) and poly(N-ethyl pyrrole) materials, and they showed near-infrared light-to-heat photothermal properties, which was confirmed by thermography. The data obtained through X-ray photoelectron spectroscopy indicated the presence of dodecyl sulfate dopants on the surface of the grains. The dried polypyrrole and poly(N-ethyl pyrrole) grains showed hydrophobic character, and therefore, they can adsorb to the air–water interface and act as a light-responsive liquid marble stabilizer. Locomotion of the liquid marble can be driven by near-infrared laser irradiation-induced Marangoni flow on a planar air–water surface. The release of internal liquid can be achieved by controlled disruption of liquid marbles via external stimulus application.Polypyrrole and poly(N-alkyl pyrrole) grains were synthesized by aqueous chemical oxidative polymerization in the presence of sodium dodecyl sulfate as both a dopant and a hydrophobizing agent. The dried polypyrrole and poly(N-ethyl pyrrole) grains showed hydrophobic character and can act as a light-responsive liquid marble stabilizer. Locomotion of the liquid marble can be driven by near-infrared laser irradiation-induced Marangoni flow on a planar air–water surface. Furthermore, the release of internal liquid can be achieved by controlled disruption of liquid marbles via external stimulus application.

The aqueous oxidative coupling polymerization of 3,4-ethylenedioxythiophene was conducted in the presence of heptadecafluorooctane sulfonic acid, which was used as a perfluoroalkyl dopant to synthesize hydrophobic poly(3,4-ethylenedioxythiophene) particles. The poly(3,4-ethylenedioxythiophene) particles were characterized in terms of their size, morphology, surface and bulk chemical compositions, conductivity, hydrophilic–hydrophobic balance and (photo)thermal properties. The electron microscopy studies confirmed that poly(3,4-ethylenedioxythiophene) consisted of aggregates of primary atypical particles of a submicrometer size. X-ray photoelectron spectroscopy and the contact angle measurement indicated that the perfluoroalkyl dopants were present on the surface of the poly(3,4-ethylenedioxythiophene) particles, which caused them to have a hydrophobic character. The electrical conductivity of the pressed pellet was 15.5 S cm−1, which was one order of magnitude higher than that of the poly(3,4-ethylenedioxythiophene) that was synthesized in the absence of the perfluoroalkyl dopant. The dried poly(3,4-ethylenedioxythiophene) particles could be used as a near-infrared-responsive liquid marble stabilizer exhibiting light-to-heat conversion properties. The movement of the poly(3,4-ethylenedioxythiophene) particle-coated liquid marbles on a planar water surface was driven by near-infrared laser-induced Marangoni propulsion. The inner liquid could be released by the disruption of the liquid marbles via an application of an external stimulus.The aqueous oxidative coupling polymerization of 3,4-ethylenedioxythiophene was conducted in the presence of heptadecafluorooctane sulfonic acid, which was used as a perfluoroalkyl dopant to synthesize hydrophobic poly(3,4-ethylenedioxythiophene) particles. The dried poly(3,4-ethylenedioxythiophene) particles could be used as a near-infrared-responsive liquid marble stabilizer exhibiting light-to-heat conversion properties. The movement of the poly(3,4-ethylenedioxythiophene) particle-coated liquid marbles on a planar water surface was driven by near-infrared laser-induced Marangoni propulsion.

In the present study, water-soluble molecular complexes between carboxylic acid-functionalized multiwalled carbon nanotubes (MWCNTs) and biocompatible poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) were prepared by hand grinding. MWCNTs could be solubilized in phosphate-buffered saline using this simple method. The suspended concentration of MWCNTs was found to increase with increasing polymer concentration and pH of the solution. Heat generation from the complexes was studied upon irradiation with near-infrared (NIR) radiation at a wavelength of 808 nm. The results demonstrated that MWCNTs absorbed light and generated heat when the molecular complex was irradiated by NIR. The solution temperature increased with increasing MWCNT concentration and irradiation time.This study presents a facile method for preparation of water-soluble molecular complexes between carboxylic acid-functionalized multiwalled carbon nanotube and poly(2-methacryloyloxyethyl phosphorylcholine) (MWCNTs/PMPC) by hand grinding. MWCNTs could be solubilized in aqueous environment with higher suspended concentrations when increasing polymer concentration and pH of the solution. MWCNTs/PMPC adsorbed light and induced heat generation to reach the temperature required for photothermal therapy (PTT) when the complexes were irradiated by near-infrared (NIR) at a wavelength of 808 nm. The water-soluble MWCNT complex covered by biocompatible PMPC is a promising candidate for PTT application.

Stimuli-responsive emulsions offer a dual advantage, combining long-term storage with controlled release triggered by external cues such as pH or temperature changes. This study establishes that thermo-responsive emulsion behaviour is primarily determined by interactions between, rather than within, interfaces. Consequently, the stability of these emulsions is intricately tied to the nature of the stabilizing microgel particles - whether they are more polymeric or colloidal, and the morphology they assume at the liquid interface. The colloidal properties of the microgels provide the foundation for the long-term stability of Pickering emulsions. However, limited deformability can lead to non-responsive emulsions. Conversely, the polymeric properties of the microgels enable them to spread and flatten at the liquid interface, enabling stimuli-responsive behaviour. Furthermore, microgels shared between two emulsion droplets in flocculated emulsions facilitate stimuli-responsiveness, regardless of their internal architecture. This underscores the pivotal role of microgel morphology and the forces they exert on liquid interfaces in the control and design of stimuli-responsive emulsions and interfaces. Stimuli-responsive emulsions are useful for long-term storage combined with controlled release, but the fundamental mechanism behind this release is not established. Here, the authors report a study into the effect of individual microgel morphology on the destabilisation of responsive emulsions.

The long-term morphological and chemical stabilities of polypyrrole grains in aqueous media (1-year duration) are investigated. Polypyrrole grains doped with chloride ions or heptadecafluorooctane sulfonic acid were extensively characterized using a wide range of analytical techniques. The average sizes of the grains were 13–15 μm and consisted of submicrometer-sized atypical primary particles. The grain size increased in the case of polypyrrole doped with chloride ions, whereas no apparent changes were observed in the case of polypyrrole doped with heptadecafluorooctane sulfonic acid after storage at pH 3 and 10. The size and morphology of the primary particles did not change for each grain system. Appreciable changes in chemical structure and surface chemistry were observed. At pH 10, dedoping occurred easily, and chloride ions and heptadecafluorooctane sulfonic acid were released from the grains in a short time (within one week). On the other hand, the dopants were released slowly at pH 3, which is likely caused by nucleophilic attack by water molecules to the polypyrrole. The release rate of the dopant was slower for polypyrrole doped with heptadecafluorooctane sulfonic acid than for polypyrrole doped with chloride ions. This finding is attributed due to the stronger hydrophobic interaction between polypyrrole and heptadecafluorooctane sulfonic acid.Long-term morphological and chemical stabilities of polypyrrole grains doped with chloride ion or heptadecafluorooctane sulfonic acid in aqueous media (1-year duration) are studied. There were appreciable changes in chemical structure and surface chemistry, although the size and morphology of the polypyrrole primary particles did not change for each grain system. The dopants were released with time, and its rate was slower for the polypyrrole doped with heptadecafluorooctane sulfonic acid, compared to that doped with chloride ion. This should be due to the stronger hydrophobic interaction between polypyrrole and heptadecafluorooctane sulfonic acid.

Surface-templated evaporation-driven (S-TED) synthesis, a technique for producing supraparticles by drying colloidal dispersion droplets on liquid-repellent surfaces, offers numerous advantages over conventional solvent-based synthesis methods. For example, the S-TED method requires no toxic solvent, heating, or additional purification steps. Moreover, this approach allows precise control of supraparticle porosity and size with a narrow size distribution. However, despite extensive efforts, only a limited range of supraparticles shapes with different curvatures have been fabricated. This work introduces a novel approach for three-dimensional manipulation of supraparticle shapes using multiple liquid-repellent surfaces as drying templates. Thin polyethylene terephthalate (PET) plates with varied wettable surfaces and shapes are used as templates. Droplets covered by the PET plates evaporate in two different modes, involving constant contact line or constant height. These modes considerably influence the shape of supraparticles. In the constant contact line mode, the shape of the PET plates determines the supraparticle shape. In addition, polyhedral shapes can be precisely fabricated by varying the numbers of the PET plates, broadening the range of achievable supraparticle shapes.

Hydrophobic skins on fruits play a crucial role in preventing dehydration and shielding against environmental stress. Inspired by this natural structure, hydrophobic encapsulation is widely employed to preserve the functionality and long-term stability of hydrogels. However, instability at the interface between hydrophobic shell and hydrogel remains a critical challenge. Here, we present a hydrogel encapsulation strategy to stabilize the incompatible interface using a concept of liquid marble, where liquid droplet is covered with hydrophobic particles. A uniform nonpolar liquid layer is first formed on the hydrogel surface through interfacial bridges with hydrophobic particles. A secondary hydrophobic particle layer is then deposited onto this liquid layer to prevent leakage, yielding a multi-layered marble (MLM) structure. This MLM-encapsulation is highly versatile, accommodating various hydrogels, liquids, and structural configurations. By maintaining hydrogel performance and functionality across diverse applications, MLM-encapsulation provides a universal and robust solution for overcoming the long-standing interfacial instability problem. Hydrogel encapsulation prevents dehydration, but maintaining interfacial stability with hydrophobic shells remains challenging. Here, the authors use a multi-layered marble strategy composed of two hydrophobic particle layers with sandwiched oil layer that stabilizes the interface.

Liquid marbles are liquid droplets encased by non‐wetting particles. They exhibit elastic and non‐sticking properties that enable applications such as sensors, adhesives, miniature reactors, and material carriers. The formation, stability, and properties of liquid marbles depend on the physico‐chemical characteristics of the solid particles. This study systematically explores the impact of particle surface roughness on liquid marbles by employing colloidal supraparticles as well‐defined model systems. Supraparticles are spherical aggregates of uniform colloidal primary particles, which enable adjusting the characteristic surface roughness by varying the primary particle size. Increasing surface roughness increases the interfacial contact angle, which, in turn, influences the mechanical properties and liquid marble stability. The presence of surface roughness increases the deformation resistance of the liquid marble, which counteracts the spreading of the inner liquid upon mechanical impact, and therefore hinders rupture. The increased contact angle further enables the formation of liquid marbles from increasingly low‐surface‐tension organic liquids. This study thus provides detailed insights into the structure‐property relationships governing the preparation of stable liquid marbles based on particle surface characteristics.