Various aspects of particle-stabilized emulsions (or so-called Pickering emulsions) have been extensively investigated during the last two decades, but the preparation of uniform Pickering emulsion droplets via a simple and scalable method has been sparingly realized. We report the preparation of uniform Pickering emulsions by Shirasu porous glass (SPG) membrane emulsification. The size of the emulsion droplets ranging from 10–50 μm can be precisely controlled by the size of the membrane pore. The emulsion droplets have a high monodispersity with coefficients of variation (CV) lower than 15% in all of the investigated systems. We further demonstrate the feasibility of locking the assembled particles at the interface, and emulsion droplets have been shown to be excellent templates for the preparation of monodisperse colloidosomes that are necessary in drug-delivery systems.

We report here a supramolecular hydrogel displaying a wide array of dynamic desirable properties. The key is using an ABA triblock copolymer containing a central poly(ethylene oxide) block and terminal poly(N-isopropylacrylamide) (PNIPAm) block with ureido pyrimidinone (UPy) moieties randomly incorporated. Rapid hydrogelation is triggered upon increasing temperature above the lower critical solution temperature (LCST) of the supramolecular copolymer, where PNIPAm segments dehydrate and assemble into micelles, which subsequently provide hydrophobic microenvironments promoting UPy dimerization to grab polymer chains, thus forming hydrogen-bonded cross-linking points. The supramolecular hydrogels demonstrate fascinating shear-thinning, self-healable, thermo-reversible, and injectable properties, which allow withstanding repeated deformations and 3D construction of complex objects. Mesenchymal stem cells mixed with the hydrogel and injected through needles remain highly viable (>90%) during the encapsulation and delivery process. With these attractive dynamic physical properties, the supramolecular hydrogel holds great promise to support cell or drug therapies.

Coating a liquid with a particle shell not only renders a droplet superhydrophobic but also isolates a well-confined microenvironment for miniaturized chemical processes. Previously, we have demonstrated that particles at the liquid marble interface provide an ideal platform for the site-selective modification of superhydrophobic particles. However, the need for a special chemical reaction limits their potential use for the fabrication of Janus particles with various properties. Herein, we combine the employment of liquid marbles as microreactors with the remarkable adhesive ability of polydopamine to develop a general route for the synthesis of Janus particles from micrometer-sized superhydrophobic particles. We demonstrate that dopamine polymerization and deposition inside liquid marbles could be used for the selective surface modification of microsized silica particles, resulting in the formation of Janus particles. Moreover, it is possible to manipulate the Janus balance of the particles via the addition of surfactants and/or organic solvents to tune the interfacial energy. More importantly, owing to the many functional groups in polydopamine, we show that versatile strategies could be introduced to use these partially polydopamine-coated silica particles as platforms for further modification, including nanoparticle immobilization, metal ion chelation and reduction, as well as for chemical reactions. Given the flexibility in the choice of cores and the modification strategies, this developed method is distinctive in its high universality, good controllability, and great practicability.

The potential application of Pickering high-internal phase emulsions (HIPEs) in the food and pharmaceutical industries has yet to be fully developed. Herein, we synthesized fairly monodisperse, nontoxic, autofluorescent gelatin particles for use as sole stabilizers for fabricating oil-in-water (O/W) HIPEs in an effort to improve the protection and bioaccessibility of entrapped β-carotene. Our results showed that the concentration of gelatin particles determined the formation, microstructure, droplet size distribution, and digestion profile of the HIPEs. For storage stability, the retention of β-carotene in HIPEs was significantly higher than in dispersion in bulk oil, even after storage for 27 days. In addition, in vitro digestion experiments indicated that the bioaccessibility of β-carotene was improved 5-fold in HIPEs. This study will help establish a correlation between the physicochemical properties of gelatin particle-stabilized HIPEs with their applications in the oral delivery of bioactive nutraceuticals.Keywords: bioaccessibility; gelatin particle; in vitro digestion; Pickering high-internal phase emulsion; β-carotene;

Total internal reflection microscopy (TIRM) measures the interactions between a colloidal particle and a flat surface in aqueous solution. Recently, TIRM has further integrated with video microscopy (VM) and enabled the simultaneous measurements of multi-particle colloid-surface interactions in the same ensemble. However, there still remain challenges about accurate image acquisition due to blooming. Blooming means the number of photons reaching the detector exceeds its maximum capacity, and the excess photons will either spill to adjacent pixels or not be counted, leading to an obstacle from precise determination of intensity. Our result shows that blooming gives rise to a deviation of the measured potential energy from the classical theory of Derjaguin, Landau, Verway, and Overbeek (DLVO). Therefore, a correction method was developed in this work to deduce the real intensity from the experimental measurement. The relationship between scattered light intensity and exposure time deviates from linearity when blooming occurs. A correction equation was developed to recover the real intensity, which was then confirmed by the accordance between the corresponding potential energy profiles and the DLVO theory. This correction method is suitable for VM systems of colloidal probes illuminated by scattered light, broadening the application of VM imaging to investigate colloidal interactions.Download high-res image (168KB)Download full-size image

•POEGMA brush layers with different thickness and graft densities were prepared by SI-ATRP method.•Interactions between polymer brush-modified surfaces and protein-coated particles were quantitatively measured by TIRM.•The adsorbed protein layers were found to regulate the interaction between particles and POEGMA modified surfaces.Hydrophilic poly[oligo(ethylene glycol) methyl methacrylate] (POEGMA) brush layers with different thickness and graft densities were prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) to construct a model surface to examine protein-surface interactions in a serum environment. The thickness of the POEGMA brush layers could be well controlled by the polymerization time and density of the immobilized initiators. The interactions between these brush-modified surfaces and the protein-coated polystyrene (PS) particles in newborn calf serum (NBCS) environment were then measured by total internal reflection microscopy (TIRM). In addition, protein adsorption properties onto the polymer brush surface layers were examined by atomic force microscopy (AFM). Relatively large amounts of protein adsorbed to short (4 nm and 9 nm-thick) POEGMA-coated surfaces or surfaces grafted with a low density of polymer chains. It was considered that shorter polymer chains or chains with low grafted density cannot fully cover the surfaces, proteins in serum could directly interact with the material surface and then deposited to form an adsorbed layer. The TIRM measurements showed that such adsorbed protein layer could mediate the interactions between the two surfaces by generating steric or bridging forces, resulting in different interaction potentials. Some particles were freely diffusing, some experienced intermittent diffusion and more than 50% of particles were irreversibly deposited to the surfaces covered by short polymer brushes. However, for longer (17 and 30 nm-thick) POEGMA brush layer surfaces, material surface would be sufficiently covered by the dense coating and the first step of protein adsorption on surface was avoided. TIRM measurements showed that around 95% of the protein-coated particles could freely move in the serum and no attractive force between two surfaces was detected. The steric repulsion generated from the long POEGMA brush layer in the swollen state was long-range and strong so that the protein adsorption is very unlikely. These results concluded that the adsorbed protein layer on POEGMA surfaces plays an important role in regulating the interaction between protein-coated particles and POEGMA surfaces which are highly repellent toward protein adsorption.Download high-res image (153KB)Download full-size image

Here we report on the successful preparation of open-cellular macroporous 3D scaffolds templated from gelatin nanoparticle-stabilized HIPEs with acrylamide (AM) as the monomer in the continuous phase. Tuning the gelatin nanoparticle concentration or AM content led to different porous structures with void diameters varying between 30 and 78 μm. More importantly, keeping HIPEs at room temperature to undergo a limited kinetic coarsening before polymerization could greatly improve the interconnectivity and pore size of the scaffolds, with the average diameters (approx. 118 μm) being enlarged 1.5-fold. Additionally, the scaffolds had a character of soft tissue with compressive modulus more than 150 kPa. The cell culture assay confirmed that HepG2 cells not only could adsorb on but also were grown inside the scaffolds, representing a characteristic of the good biocompatibility of the scaffolds. Our work suggests that the 3D scaffolds fabricated from gelatin nanoparticle-stabilized HIPE templates are promising culture substrates for a wide range of applications in the biomedical field.

Nanoparticles at the air/liquid interface can serve as solid separating barriers to form stable foams or liquid marbles depending on the wettability of the nanoparticles. This paper presents an effect that enables the insertion and confinement of air bubbles inside a liquid marble, based on encapsulating an air bubble surrounded by surfactant molecules or hydrophilic particles. We have demonstrated that more than one bubble can be inserted and trapped inside one liquid marble so that liquid marbles can be divided into several separate compartments. The findings presented here may stimulate fundamental studies of this novel bubble-marble phenomenon, as well as developments of various practical applications.

HypothesisResponsive poly(N-isopropylacrylamide) microgel (PNIPAM microgel) stabilized Pickering emulsions were investigated in this study. A recent theoretical study of other researchers has suggested that large soft particles at the oil/water interface are less deformable than their small counterparts. Therefore, we expected that our micron-sized microgel particles might not significantly deform at the oil/water interface.ExperimentsWe applied confocal laser scanning microscopy (CLSM) to examine the structure of soft PNIPAM-based microgel particles at the decane–water interface in a microgel-stabilized emulsion. Using micron-sized microgel particles with better labelling techniques, we could compensate the weakness in resolution of using CLSM. Seven PNIPAM-based microgel samples with various softness values and morphologies were examined at different pH values.FindingsOur results demonstrate that the deformation of ordinary micron-sized microgel samples was not significant if they were not in the pH-swollen state. Nevertheless, the soft, pH-swollen microgel particles exhibited anisotropic deformation at the decane–water interface. Such flattening was not reported in previous studies. The studies of microgel particles at the oil–water interface with different imaging techniques and their comparison are valuable to help to elucidate the particles’ roles in stabilizing the Pickering emulsions.Confocal laser scanning microscopy (CLSM) was applied to examine the structure of responsive soft PNIPAM microgel particles at decane/water interface in a microgel-stabilized emulsion. The deformation of ordinary, micron-sized microgel samples was not significant if they were not at pH-swollen state. However, the soft, pH-swollen microgel particles showed anisotropic deformation at the decane–water interface.

In this work, we applied total internal reflection microscopy (TIRM) to directly measure the interactions between three different kinds of macroscopic surfaces: namely bare polystyrene (PS) particle and bare silica surface (bare-PS/bare-silica), PS particle and silica surfaces both coated with bovine serum albumin (BSA) (BSA-PS/BSA-silica), and PS particle and silica surfaces both modified with polyethylene glycol (PEG) (PEG-PS/PEG-silica) polymers, in phosphate buffer solution (PBS) and fetal bovine serum (FBS). Our results showed that in PBS, all the bare-PS, BSA-PS, and PEG-PS particles were irreversibly deposited onto the bare silica surface or surfaces coated either with BSA or PEG. However, in FBS, the interaction potentials between the particle and surface exhibited both free-diffusing particle and stuck particle profiles. Dynamic light scattering (DLS) and elliposmeter measurements indicated that there was a layer of serum proteins adsorbed on the PS particle and silica surface. TIRM measurement revealed that such adsorbed serum proteins can mediate the surface–surface interactions by providing additional stabilization under certain conditions, but also promoting bridging effect between the two surfaces. The measured potential profile of the stuck particle in FBS thus was much wider than in PBS. These quantitative measurements provide insights that serum proteins adsorbed onto surfaces can regulate surface–surface interactions, thus leading to unique moving behavior and stability of colloidal particles in the serum environment.

The assembly and manipulation of charged colloidal particles at oil/water interfaces represent active areas of fundamental and applied research. Previously, we have shown that colloidal particles can spontaneously generate unstable residual charges at the particle/oil interface when spreading solvent is used to disperse them at an oil/water interface. These residual charges in turn affect the long-ranged electrostatic repulsive forces and packing of particles at the interface. To further uncover the influence arising from the spreading solvents on interfacial particle interactions, in the present study we utilize pure buoyancy to drive the particles onto an oil/water interface and compare the differences between such a spontaneously adsorbed particle monolayer to the spread monolayer based on solvent spreading techniques. Our results show that the solvent-free method could also lead particles to spread well at the interface, but it does not result in violent sliding of particles along the interface. More importantly, this additive-free spreading method can avoid the formation of unstable residual charges at the particle/oil interface. These findings agree well with our previous hypothesis; namely, those unstable residual charges are triboelectric charges that arise from the violently rubbing of particles on oil at the interface. Therefore, if the spreading solvents could be avoided, then we would be able to get rid of the formation of residual charges at interfaces. This finding will provide insight for precisely controlling the interactions among colloidal particles trapped at fluid/fluid interfaces.

Surface modification of the nanoparticles using surface anchoring of amphiphilic polymers offers considerable scope for the design of a wide range of brush-coated hybrid nanoparticles with tunable surface wettability that may serve as new class of efficient Pickering emulsifiers. In the present study, we prepared mixed polymer brush-coated nanoparticles by grafting ABC miktoarm star terpolymers consisting of poly(ethylene glycol), polystyrene, and poly[(3-triisopropyloxysilyl)propyl methacrylate] (μ-PEG-b-PS-b-PIPSMA) on the surface of silica nanoparticles. The wettability of the as-prepared nanoparticles can be precisely tuned by a change of solvent or host–guest complexation. 1H NMR result confirmed that such wettability change is due to the reorganization of the polymer chain at the grafted layer. We show that this behavior can be used for stabilization and switching between water-in-oil (W/O) and oil-in-water (O/W) emulsions. For hairy particles initially dispersed in oil, W/O emulsions were always obtained with collapsed PEG chains and mobile PS chains at the grafted layer. However, initially dispersing the hairy particles in water resulted in O/W emulsions with collapsed PS chains and mobile PEG chains. When a good solvent for both PS and PEG blocks such as toluene was used, W/O emulsions were always obtained no matter where the hairy particles were dispersed. The wettability of the mixed polymer brush-coated silica particles can also be tuned by host–guest complexation between PEG block and α-CD. More importantly, our result showed that surprisingly the resultant mixed brush-coated hairy nanoparticles can be employed for the one-step production of O/W/O multiple emulsions that are not attainable from conventional Pickering emulsifiers. The functionalized hairy silica nanoparticles at the oil–water interface can be further linked together utilizing poly(acrylic acid) as the reversible linker to form supramolecular colloidosomes, which show pH-dependent release of cargo.Keywords: hairy particles; multiple emulsions; Pickering emulsions; wettability;

•PNIPAM-based microgels with controlled crosslink distributions were synthesized.•PNIPAM-co-PMAA microgels with controlled charge distributions were synthesized.•Crosslink distribution influences temperature-dependent deswelling of microgels.•Charge distribution influences microgel swelling in response to pH.Microgels are soft particles that consist of chemically cross-linked three-dimensional polymer networks. They are usually synthesized by precipitation polymerization. However, this method often leads to an inhomogeneous spatial distribution of crosslinks and functional groups within the microgel particles caused by differences in the reactivity ratios of the applied monomers, co-monomers, and crosslinkers. This lack of control of the structure has a profound effect on the properties of microgels, which in turn significantly limits their applications. In this work, poly(N-isopropylacrylamide) (PNIPAM)-based microgels with controlled distribution of crosslinks and charges were synthesized by batch polymerization or starve-feeding semi-batch polymerization. The structures of microgels with different crosslink distributions were characterized by laser light scattering (LLS). Our results show that the distributions of crosslinks influence the deswelling behaviors of microgels in response to temperature. When organic acid like methacrylic acid (MAA) was incorporated into the microgel, the resulting microgel particles added responsiveness to pH. The charge distributions, namely the spatial distribution of the functional MMA groups in the microgels were verified by potentiometric titration and electrophoresis. These microgels exhibit different swelling properties in response to pH. The developed approach for improving control of functional group distribution in microgels is essential for the design of more advanced microgel structures for specific applications.

In recent years, inorganic nanoparticles such as Laponite have frequently been incorporated into polymer matrixes to obtain nanocomposite hydrogels with hierarchical structures, ultrastrong tensibilities, and high transparencies. Despite their unique physical and chemical properties, only a few reports have evaluated Laponite-based nanocomposite hydrogels for biomedical applications. This article presents the synthesis and characterization of a novel, hemocompatible nanocomposite hydrogels by in situ polymerization of acrylamide (AAm) in a mixed suspension containing Laponite and gelatin. The compatibility, structure, thermal stability, and mechanical properties of the resulting NC gels with varied gel compositions were investigated. Our results show that the prepared nanocomposite hydrogels exhibit good thermal stability and mechanical properties. The introduction of a biocompatible polymer, gelatin, into the polymer matrix did not change the transparency and homogeneity of the resulting nanocomposite hydrogels, but it significantly decreased the hydrogel’s pH-responsive properties. More importantly, gelatins that were incorporated into the PAAm network resisted nonspecific protein adsorption, improved the degree of hemolysis, and eventually prolonged the clotting time, indicating that the in vitro hemocompatibility of the resulting nanocomposite hydrogels had been substantially enhanced. Therefore, these nanocomposite hydrogels provide opportunities for potential use in various biomedical applications.Keywords: gelatin; hemocompatible; Laponite; nanocomposite hydrogels; PAAm

•This short review demonstrates the use of TIRM in measuring depletion interaction between the particle–surface mediated by polymers, polyelectrolytes, and charged nanoparticles with different softness.•We discuss the detailed connection between neutral polymer density in bulk, the addition of nanoparticles, and soft microgels to the induced interaction.The entropic depletion interaction has been the subject of several studies over the past decade because it plays an important role in many industrial applications and also involves in controlling biological interactions. In this short review, we discuss recent developments associated with using nonintrusive optical techniques for directly measuring kBT-scale depletion interaction. In particular, we limit the scope of this review to the use of total internal reflection microscopy (TIRM) for quantitative measurements of interactions between a single, colloidal particle and a flat surface mediated by the presence of neutral polymers, polyelectrolytes, and charged nanoparticles with different softness based on our recent works. Finally, we conclude with some perspectives on future research efforts in this field.This short review discusses the use of total internal reflection microscopy (TIRM) for quantitative measurements of interactions between a single, colloidal particle and a flat surface mediated by the presence of neutral polymers, polyelectrolytes, and charged nanoparticles with different softness.

•PNIPAM microgels were synthesized and used to construct thermo-responsive surfaces.•A PEI underlayer is indispensable to prepare uniform surfaces via drop-coating.•HepG2 cells fail to detach from the PNIAPM microgel films upon cooling.•Irreversible adsorption of serum proteins may account for the cell behavior.The use of poly(N-isopropylacrylamide) (PNIPAM) as building blocks for engineering responsive coatings and their potential use as switchable substrates such as biosensors have attracted great attention in recent years. However, few studies have been conducted regarding the cell behaviors and the related mechanism on thermos-responsive surfaces consisting of PNIPAM microgel particles. In this work, monodisperse PNIPAM microgels were synthesized and used to prepare PINPAM microgel films. Uniform microgel surfaces can be fabricated by drop-coating with the precoating of a polyethylenimine (PEI) layer. Cell experiments indicate that unlike PNIPAM polymer brushes reported with controllable detachment ability, HepG2, which is a human liver carcinoma cell line, remains adherent on the microgel films upon cooling. Surface plasmon resonance (SPR) experiments show an irreversible adsorption of serum proteins on the microgel surface upon cooling, whose adsorption is a prerequisite of cell adhesion during cell culture. This fact may account for the irreversible adhesion of HepG2 cells.

Understanding the interaction between protein-functionalized surfaces is an important subject in a variety of protein-related processes, ranging from coatings for biomedical implants to targeted drug carriers and biosensors. In this work, utilizing a total internal reflection microscope (TIRM), we have directly measured the interactions between micron-sized particles decorated with three types of common proteins concanavalin A (ConA), bovine serum albumin (BSA), lysozyme (LYZ), and glass surface coated with soy proteins (SP). Our results show that the protein adsorption greatly affects the charge property of the surfaces, and the interactions between those protein-functionalized surfaces depend on solution pH values. At pH 7.5–10.0, all these three protein-functionalized particles are highly negatively charged, and they move freely above the negatively charged SP-functionalized surface. The net interaction between protein-functionalized surfaces captured by TIRM was found as a long-range, nonspecific double-layer repulsion. When pH was decreased to 5.0, both protein-functionalized surfaces became neutral and double-layer repulsion was greatly reduced, resulting in adhesion of all three protein-functionalized particles to the SP-functionalized surface due to the hydrophobic attraction. The situation is very different at pH = 4.0: BSA-decorated particles, which are highly charged, can move freely above the SP-functionalized surfaces, while ConA- and LYZ-decorated particles can only move restrictively in a limited range. Our results quantify these nonspecific kT-scale interactions between protein-functionalized surfaces, which will enable the design of surfaces for use in biomedical applications and study of biomolecular interactions.

Pickering emulsions stabilized by solid particles have been widely studied in the past decades due to improved stability and reduced use of small molecular surfactants. Recently, the application of Pickering emulsions in pharmaceutics has been attracting increasing attention but very limited practical use has been demonstrated, because most of the investigated particles possess poor biodegradability, which is inappropriate in pharmaceutics. Some reported biodegradable particles were too hydrophilic to stabilize emulsions, which needs further particle modification or additional surfactants. Fortunately, biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA) with tunable hydrophilicity makes itself a promising material to prepare Pickering emulsions. However, the mechanism of emulsion stabilization still remains unknown. Moreover, fabrication of large amounts of uniform-sized and size-controlled PLGA particles by traditional methods is very difficult, which further increases the difficulty to perform the research. In the present study, we applied Shirasu Porous Glass (SPG) premix membrane emulsification to solve this problem. The stabilization mechanism of Pickering emulsions stabilized by PLGA particles was systematically studied for the first time. The factors including oil type, particle properties, concentration, molecular weight (Mw) and oil–water volume ratio were analyzed through particle wettability and interfacial influence. We found that octanol was an appropriate oil type, and its small particle size, high particle concentration and high Mw were favorable for emulsion stability. By changing the oil–water volume ratio, stable emulsions were also readily achieved. These studies proved that Pickering emulsions stabilized by PLGA particles had wide potential applications in pharmaceutics and tissue engineering.

Colloidosomes are microcapsules that consist of a hollow core coated by a shell composed of self-assembled colloidal particles. In recent years, they have attracted significant attention as potential vehicles for the controlled delivery of active ingredients. A key challenge in such applications is the production of uniform-sized colloidosomes for the encapsulation of active ingredients such that the actual delivery amount can be well controlled. Based on our previous study on an ethyl acetate-in-water emulsion stabilized by chitosan-coated alginate particles, we further prepared monodisperse colloidosomes with a high yield and low permeability by combining the premix membrane emulsification technique and polymer deposition method. The potential application of the formed colloidosomes as oral insulin delivery vehicles was investigated. Our results revealed that in comparison to conventional PLGA microspheres, the formulated colloidosomes showed high drug encapsulation efficiency (up to 96.7%) and an obvious pH sensitive release profile. Moreover, in animal testing, the colloidosomes formulation achieved a long-term hypoglycemic effect up to 6 h, which confirmed its application as an oral drug delivery system.

In this paper, we report for the first time the use of a well-dispersed gelatin particle as a representative of natural and biocompatible materials to be an effective particle stabilizer for high internal phase emulsion (HIPE) formulation. Fairly monodispersed gelatin particles (∼200 nm) were synthesized through a two-step desolvation method and characterized by dynamic light scattering, ζ-potential measurements, scanning electron microscopy, and atomic force microscopy. Those protein latexes were then used as sole emulsifiers to fabricate stable oil-in-water Pickering HIPEs at different concentrations, pH conditions, and homogenization times. Most of the gelatin particles were irreversibly adsorbed at the oil–water interface to hinder droplet coalescence, such that Pickering HIPEs can be formed by a small amount of gelatin particles (as low as 0.5 wt % in the water phase) at pH far away from the isoelectric point of the gelatin particles. In addition, increasing homogenization time led to narrow size distribution of droplets, and high particle concentration resulted in more solidlike Pickering HIPEs. In vitro controlled-release experiments revealed that the release of the encapsulated β-carotene can be tuned by manipulating the concentration of gelatin particles in the formulation, suggesting that the stable and narrow-size-distributed gelatin-stabilized HIPEs had potential in functional food and pharmaceutical applications.Keywords: controlled release; gelatin particle; high internal phase emulsion; nutraceutical containers; Pickering emulsion

Non-covalent intermolecular forces, such as van der Waals, electrostatic, steric, and hydrophobic interactions, have played essential roles in determining the association, aggregation, adhesion and sedimentation processes of colloidal particles, surfactant micelles, and macromolecules, in solutions and biological systems. These interaction forces, however, are normally weak (<pN) and are challenging and difficult to be directly measured by common force techniques. In this feature article, we discuss recent advances in the development of the non-intrusive optical technique of Total Internal Reflection Microscopy (TIRM) for studying the interactions between a single colloidal particle and a flat surface. We begin with a brief overview of quantitative measurements of particle–surface interactions in aqueous solutions, and then show recent developments associated with TIRM for measuring kT-scale interactions between a single particle and surface in the presence of polymer chains, micelles, and colloidal particles with different softness based on our recent work. We also highlight how TIRM can be used to measure particle–surface interactions after the particle and the flat surface are physically adsorbed or grafted with polyelectrolytes, as well as to investigate the non-specific and specific interactions between proteins and protein–carbohydrate in biological systems. Lastly, we conclude with some perspectives on future research efforts in this field.

Understanding the interfacial properties of soft poly(N-isopropylacrylamide) (PNIPAM) microgels covering an oil–water interface is essential for engineering stimuli-responsive emulsions stabilized by soft microgel particles. This study presents a systematic study on the interfacial properties of the PNIPAM-microgel-laden heptane–water interface as a function of temperature. We measured the interfacial tensions as well as dilatational rheology properties of the microgel-laden heptane–water interface using a pendant drop tensiometer. From fresh droplet experiments, the anomalous interfacial tension minima of the microgels covered oil–water interface were observed around the volume phase transition temperature (VPTT) of the PNIPAM microgels. Such interfacial tension minima are observable regardless of the microgel aggregates. Both dynamic and static parameters contributed to the observed interfacial tension minima around VPTT. The PNIPAM microgel deformability dynamically dominated the microgel spreading at the heptane–water interface in the early states, while PNIPAM microgel packing and interactions dominated the final static equilibrium states. Combining the interfacial tension and the dilatational rheology properties, we propose that the microgels would approach three distinctive states at temperatures below, around, and above VPTT at the heptane–water interface. Single droplet experiments further demonstrate that there exists an irreversible transition among these three states. The results of this study deepen our understanding of soft, porous, and deformable microgels' behaviors at the oil–water interface and have important implications for engineering microgels as stimuli-responsive emulsion stabilizers.

The coating of solid particles on the surface of liquid in air makes liquid marbles a promising approach in the transportation of a small amount of liquid. The stabilization of liquid marbles by polymeric latex particles imparts extra triggers such as pH and temperature, leading to the remote manipulation of droplets for many potential applications. Because the functionalized polymeric latexes can exist either as colloidally stable latex or as flocculated latex in a dispersion, the drying of latex dispersions under different conditions may play a significant role in the stabilization of subsequent liquid marbles. This article presents the investigation of liquid marbles stabilized by poly(styrene-co-methacrylic acid) (PS-co-MAA) particles drying under varied conditions. Protonation of the particles before freeze drying makes the particles excellent liquid marble stabilizers, but it is hard to stabilize liquid marbles for particles dried in their deprotonated states. The static properties of liquid marbles with increasing concentrations of protonating reagent revealed that the liquid marbles are gradually undermined by protonating the stabilizers. Furthermore, the liquid marbles stabilized by different particles showed distinct behaviors in separation and merging manipulated by tweezers. This study shows that the initial state of the particles should be carefully taken into account in formulating liquid marbles.

Due to the softness and deformability, interaction between colloidal surfaces induced by soft particles varies in a more complex way than for solid particles and thus has attracted much attention in recent years. In the present study, we use total internal reflection microscopy (TIRM) to directly measure the interaction between polystyrene (PS) microparticles and a flat glass surface in a poly(N-isopropylacrylamide) (PNIPAM) microgel dispersion with concentration varying from dilute (0.1 wt %) to highly concentrated regime (7.5 wt %). Our result shows that the PS particle–surface interactions mediated by the soft microgels are greatly affected by the particle concentration, the configuration of those microgels adsorbed on the surfaces, and the structure and packing of microgels in bulk solution. With increasing the microgel concentration (Cmicrogel), the interaction between the PS particle and surface turned from bridging attraction to steric repulsion, and then depletion attraction, which were mainly governed by the adsorption amount and configuration of microgels on the two surfaces. By further increasing Cmicrogel to condensed situation, structural force with oscillated energy wells was detected. The variation of interactions induced by the soft microgels was further confirmed by optical imaging. Crystallization of the PS microparticles appeared at moderate Cmicrogel; however, crystallization was hindered at higher Cmicrogel where the microgels are highly packed in the bulk solution. Furthermore, using TIRM, microgel packing with local energy well (0.1–1.0 kBT) at the highly condensed state (7.5 wt %) was resolved from the interaction profiles. Therefore, the shear force and modulus generated by such microgel packing can be determined as ∼0.2 pN and tens of mPa, respectively, which are much weaker than data given by conventional active methods.

Although the carbohydrate–lectin interactions have been intensively investigated, there is little report concerning the factors that affect the carbohydrate–lectin interaction. The interactions between concanavalin A (Con A) and glycopolymers, namely poly(2-(methacrylamido)-glucopyranose) and poly(2-methacrylamido-2-deoxy-glucitol) containing pyranose ring form and open form of glucosamine, respectively, have been investigated by a combination of isothermal titration calorimetry and quartz crystal microbalance-dissipation. Our results show that not only the pyranose ring form of glucosamine but also the open form can bind to Con A. Moreover, we investigate the influence of temperature on the carbohydrate–lectin interaction. As the temperature increases, the carbohydrate–lectin interaction is enhanced.

•Uniform-sized alginate particles of different sizes were controllably prepared.•Stable Pickering emulsions were fabricated by chitosan coated alginate particles.•Particle size, pH and salt concentration had huge effects on emulsion stability.Owing to the absence of surfactants, Pickering emulsion shows little toxicity and emerges as an alternative for preparing potential carriers in biomedical area. Alginate particles are attractive stabilizers for this emulsion owing to their biocompatibility and pH sensitivity. However, their performance is still dissatisfactory due to the difficulty in preparing uniform submicron particles and the inappropriate hydrophilic property. In this study, we developed two strategies to circumvent above shortcomings. Uniform alginate particles with submicron to micron size were successfully prepared by premix membrane emulsification. In addition, the uniform particles were coated with relatively hydrophobic chitosan to overcome the high hydrophilicity of alginate particles. These uniform coated particles effectively stabilized the oil-in-water Pickering emulsion. It was found that the stability of emulsions was tremendously affected by particle size, and the least particle concentrations required for emulsion stability were proportional to the particle radii. Besides the particle size, the pH and salt concentration of aqueous phase was demonstrated to impact the stability of emulsions. The underlying mechanism was discussed in detail, concerning with three different-sized particles. Present work provided an effective strategy to prepare Pickering emulsion, which can be applied to design potent carriers in biomedical area.

•Multiple emulsions with long-term stability can be formed in one-step phase inversion process by using synthesized block copolymer as the stabilizer.•The correlation between the nature of the block copolymer including the hydrophilic-to-hydrophobic segment ratio on multiple emulsion formation and stability has been examined.•This study provides a valuable guidance toward the catastrophic phase inversion and the preparation of stable multiple emulsions using classical block copolymers as stabilizers.Multiple emulsions have attracted significant interests for fundamental study and practical applications. However, the preparation of stable multiple emulsions is difficult in general because the emulsification often involves a two-step process as well as two kinds of surfactants are needed to stabilize the two thermodynamically unstable interfaces. Recently, we described a one-step inversion approach for fabricating multiple emulsions with long-term stability by using a precisely defined amphiphilic copolymer, poly(ethylene glycol)-b-polystyrene (PEG-b-PS), as sole surfactant. Herein we examine the correlation of the nature of this block copolymer with its emulsification performance in more details. Our result shows that the asymmetric ratio, namely the ratio of block length between PS and PEG of the synthesized diblock copolymer, has a great influence on the catastrophic phase inversion as well as the type and stability of the resulting emulsions. The symmetric block copolymer with the asymmetric value close to 1 can lead to stable multiple emulsions because they might have the highest surface covering density not only at the oil-in-water (O/W) normal emulsion interface, but also at the water-in-oil (W/O) inverse emulsion interface. For highly asymmetric block copolymer like PEG45-b-PS150, only W/O emulsion is obtained as the longer PS block will increase the hydrophobicity of the polymer and then it will be preferentially wetted by oil. However, for asymmetric PEG45-b-PS6 block copolymer with shorter PS block, it leads to very different catastrophic phase inversion depending on whether the micelles are formed in the aqueous phase.The asymmetric ratio, namely the ratio of block length between PS and PEG of diblock copolymer, has a dramatic influence on the catastrophic phase inversion as well as the type and stability of the resulting emulsions.

We report a facile method for preparing porous structured TiO2 materials by templating from Pickering high-internal phase emulsions (HIPEs). A Pickering HIPE with an internal phase of up to 80 vol %, stabilized by poly(N-isopropylacrylamide)-based microgels and TiO2 solid nanoparticles, was first formulated and employed as a template to prepare the porous TiO2 materials with an interconnected structure. The resultant materials were characterized by scanning electron microscopy, X-ray diffraction, and mercury intrusion. Our results showed that the parent emulsion droplets promoted the formation of macropores and interconnecting throats with sizes of ∼50 and ∼10 μm, respectively, while the interfacially adsorbed microgel stabilizers drove the formation of smaller pores (∼100 nm) throughout the macroporous walls after drying and sintering. The interconnected structured network with the bimodal pores could be well preserved after calcinations at 800 °C. In addition, the photocatalytic activity of the fabricated TiO2 was evaluated by measuring the photodegradation of Rhodamine B in water. Our results revealed that the fabricated TiO2 materials are good photocatalysts, showing enhanced activity and stability in photodegrading organic molecules.

Various aspects of particle-stabilized emulsions (or so-called Pickering emulsions) have been extensively investigated during the last two decades, but the preparation of uniform Pickering emulsion droplets via a simple and scalable method has been sparingly realized. We report the preparation of uniform Pickering emulsions by Shirasu porous glass (SPG) membrane emulsification. The size of the emulsion droplets ranging from 10–50 μm can be precisely controlled by the size of the membrane pore. The emulsion droplets have a high monodispersity with coefficients of variation (CV) lower than 15% in all of the investigated systems. We further demonstrate the feasibility of locking the assembled particles at the interface, and emulsion droplets have been shown to be excellent templates for the preparation of monodisperse colloidosomes that are necessary in drug-delivery systems.

Well-defined polyurethane (PU)-based grafted copolymers with poly(2-(dimethylamino)ethyl methacrylate) (PDEM) side chains were prepared by a combination of radical polymerization and condensation reaction. They can self-assemble in water to form nanoparticles with PU as the core and hydrophilic PDEM chains as the shell. Tuning the pH value of the solutions allowed these nanoparticles to stabilize either oil-in-water (O/W) or water-in-oil (W/O) Pickering emulsions. Stable O/W emulsions were obtained with PU-based nanoparticles in the pH 3–5 or pH 11–12 range due to their better affinity to the aqueous phase. In contrast, changing the pH value to the range of 8–9 significantly changed the stabilizing behavior of the nanoparticles, leading to the formation of stable W/O emulsions. Additionally, the effect of oil polarity on the emulsification behavior of the PU-based nanoparticles was investigated. For highly non-polar oil like n-hexane, only O/W emulsions were generated and the resulting emulsions showed no response to pH change.

Microgels are colloidal gel particles that consist of chemically cross-linked three-dimensional polymer networks. They are able to dramatically swell or shrink in response to a variety of external stimuli such as temperature, pH, ionic strength, electric field, and enzyme activities. Very recently, microgel particles were employed as stabilizers for emulsions. Being soft, porous and stimuli sensitivity, it has been shown that emulsions stabilized by these microgel particles can offer an unparalleled degree of control on emulsions' stability, well beyond what can be achieved by using small molecular surfactants or conventional solid colloidal particles. In this feature article, we review recent studies where microgel particles were employed as emulsion stabilizers, focusing on the behavior of microgel particles at the liquid–liquid interfaces. We also highlight that emulsions stabilized by soft microgel particles can serve as a template for the fabrication of novel functional materials which will have a great potential to be applied in a variety of applications.

Novel polymeric microspheres with a hierarchical porous structure are facilely fabricated using double Pickering emulsion templates. This unique hierarchical porous structure makes them excellent candidates for adsorption and catalyst scaffold materials.

The manufacturing of switchable surfaces can be achieved when polymer chains are adsorbed or grafted densely on solid surfaces. These so-called “smart” surfaces have been often used to control the adsorption of various colloidal particles and biomolecules. To have an insight into the adsorption process, knowledge of the interaction forces between the surface and colloidal particle or biomolecule is critical. In this work, we used Total Internal Reflection Microscopy (TIRM) to directly measure the interaction potentials between poly(2-(dimethylaminoethyl methacrylate)) (PDMAEMA) brushes with two different lengths grafted on a glass slide and a positively charged polystyrene (PS) particle with pre-adsorbed layers of poly(ethyleneimine) (PEI, Mw = 2000 g mol−1), in aqueous solutions. As can be shown by direct interaction measurements, the interactions were strongly affected by the conformation of the polyelectrolyte brushes, pH values and salt concentrations. For short polymer brushes (∼30 nm), at pH 4.2 and 3.5 the interaction between the partially protonated and swollen PDMAEMA brush and the positively charged PS particle was dominated by repulsive forces at low salt concentrations, originating from diffuse layer overlap. However, when the pH is decreased to 3.0, a long-range attraction sets in. For longer polymer brushes (∼75 nm), the influences of the pH and salinity were more complex. Our results showed that the interaction between the longer polymer brushes and the particle could be switched reversibly between pure repulsion at pH 4.0, medium attraction at pH 3.6 and strong attraction at pH 3.0. The interaction mechanisms that act at these pH values and salt concentrations were discussed.

Understanding the adsorption behaviors of soft poly(N-isopropylacrylamide) (PNIPAM) microgels to the oil–water interface has become increasingly important both in terms of fundamental science and applications of microgels as multi-stimuli responsive emulsion stabilizers. In the present work, we used pendant drop tensiometry to trace the evolution of oil–water interfacial tensions. We investigated two PNIPAM microgels with different cross-link density as well as poly(styrene-co-NIPAM) particles. We found that the adsorption of microgels from the aqueous phase to the oil–water interface is dominated by two steps. Microgels first diffuse to the oil–water interface and this diffusion process depends on microgel concentration in the bulk phase. The second process involves the deformation and spreading of microgels at the interface. The second process depends strongly on microgel deformability. The behavior of the different microgel systems is compared with conventional Pickering stabilizers and proteins. Our results demonstrate that the softness of the microgels dominates their properties at the oil–water interface. The change of microgel shape at the interface resembles the unfolding transitions observed with proteins. On the other hand, microgels are distinctly different from conventional, rigid Pickering stabilizers.

This work presents a facile approach to produce a novel type of Janus microspheres with dual anisotropy of porosity and magnetism based on Pickering-type double emulsion templates. A stable aqueous Fe3O4 dispersion-in-oil-in-water (WF/O/W) double Pickering emulsion is first generated by using hydrophobic silica and hydrophilic mesoporous silica particles as stabilizers. Janus microspheres with multihollow structure possessing magnetite nanoparticles concentrated on one side of the microspheres are obtained after polymerization of the middle oil phase of the double emulsion under a magnetic field. The resultant Janus microspheres are characterized by optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDX). Moreover, we have systematically investigated the influences of Fe3O4 particle concentration, hydrophobic silica particle content, and volume ratio of the inner water phase to middle oil phase (WF/O) on the double emulsion formation and consequently on the structure of the resulting Janus microspheres. Our results show that the distribution of the multihollow structures within the prepared microspheres can be accurately tailored by adjusting the ratio of WF/O. In addition, the obtained Janus microsphere can be fairly orientated under a magnetic field, making them a potential candidate for synthesizing Janus membrane.

Poly(ethylenimine) (PEI) polyelectrolytes have been widely used to tune the stability, rheology, or adhesion properties of colloidal suspensions due to their strong tendency to adsorb to solid surfaces. They have also gained importance as gene carriers in biomedical applications, in which the anionic DNA chains are complexed and condensed to form PEI/DNA polyplexes. Some reported literatures have recently shown that the overdosed PEI chains, which are free in the solution mixture, also play a vital role in promoting the gene transfection, but the reason is unclear. In this work, we present the results of using total internal reflection microscopy (TIRM) to measure the interaction forces between a Brownian colloidal sphere and a flat glass plate in the presence of overdosed free PEI cationic chains, when both surfaces were saturated adsorbed with the PEI chains. The colloidal sphere preadsorbed with PEI chains was chosen to mimic the PEI/DNA polyplex. Results for the potential energy of interaction measured for model polyplex (e.g., PEI-coated sphere) interacting with a PEI-coated glass surface in the presence of overdosed free PEI chains at various pH values and salt concentrations were presented. As can be shown by direct force measurements, the interaction potentials in NaCl salt solution are dominated by repulsive forces originating from diffuse layer overlap and gravitational attraction. However, the presence of free PEI chains in the solution mixture produces a long-ranged (>60 nm) attractive force between two PEI-coated surfaces with the range and magnitude tunable by pH value, PEI, and salt concentrations. The possible mechanisms of this long-ranged attractive force are discussed. A better understanding of this free PEI-induced attractive force will be useful in the development of improved PEI/DNA polyplexes systems for biomedical applications.

Using total internal reflection microscopy (TIRM), we have systematically measured the interactions between a microsphere and a flat hydrophilic surface in the presence of polyethylene oxide (PEO) polymer solution. Our results reveal that PEO significantly mediates the interaction forces between the two surfaces. At low polymer concentration, the interactions between two surfaces in the presence of PEO are mainly dominated by repulsive forces, originating from diffuse layer overlap. At intermediate polymer concentration, a long-range and weak attraction sets in. This force is likely attributed to the depletion attraction due to the presence of free PEO chains in bulk solution; however, a simple hard-sphere AO model fails to precisely describe the attraction. At high polymer concentration where PEO chains overlap, the attraction disappears, and levitation of the microsphere probe is detected. We argue that at this overlapping region, the correlation length of PEO chains is much smaller than the size of single PEO molecule, leading to weakening and disappearing of the depletion attraction. Finally, at very high concentration, oscillatory structural force is obviously found, indicating the significant structural ordering of the PEO chains under confinement.

This Article presents the controlling synthesis and characterization of micrometer-sized, multiresponsive poly(N-isopropylacrylamide-co-methacrylic acid) (PNIPAM-MAA) microgel particles. By combining semibatch and temperature-programmed surfactant-free precipitation polymerization, we have successfully developed a novel approach to the preparation of temperature- and pH-responsive PNIPAM microgels with a dense-shell (DS), dense-core (DC), or homogeneous (HOMO) structure. We then investigated the interaction between the synthesized microgels and some fluorescent dye molecules using confocal laser scanning microscopy (CLSM). Our results have qualitatively revealed that the cross-linkers and the functional carboxylic groups (−COOH) could be homogeneously distributed, predominately localized inside the core, or concentrated near the surface of the synthesized microgels. Moreover, pH-responsive swelling behaviors of the microgels were investigated and discussed with titration and CLSM data. We found that the swelling capability is strongly dependent on the morphology of the PNIPAM microgel. Besides the absorption of fluorescent molecules, the synthesized microgels also showed a strong affinity for fluorescently labeled polypeptide, even at a relatively high salt concentration.

Cationic poly(2-(methacryloyloxy)ethyl trimethylammonium chloride) (PMETAC) brushes are grown from glass slides via surface-initiated atom transfer radical polymerization (SI-ATRP). The interaction potential energy between the surface-grown polyelectrolyte brushes and a 5 μm diameter polystyrene (PS) particle in different electrolyte environments (NaCl and NaClO4) has been directly measured using total internal reflection microscopy (TIRM). At a NaCl concentration of 0.05 mM, the measured interaction potential energy profiles show a long-range repulsion, arising from an electrical double layer interaction between the positively charged PS particle and the charges from the PMETAC layers. Upon addition of 1 mM NaCl, screening effects reduce the separation distance (h) between the PS particle and the surface, accompanied by the collapse of the PMETAC brushes. However, when the sample solution is replaced with a low concentration NaCl (0.05 mM) solution, h returns to the original values, indicating that the brushes resume the extended conformation. A remarkable difference is observed when similar TIRM experiments are carried out in the presence of NaClO4 solution. At the same concentration or ionic strength, NaClO4 causes a much more abrupt decrease in h between the particle and surface than that with NaCl solution. Conversely, flushing the sample cell with highly diluted NaClO4 or pure water cannot restore the original interaction potentials, thus implying an irreversible collapse of the PMETAC brushes in the presence of ClO4− anions. This apparent change in the PMETAC brush characteristics can be associated with the strong ion-pairing interaction between the ClO4− anions and the quaternary ammonium group in the PMETAC brushes, which experiences not only pure charge screening, but also a sharp hydrophilic-to-hydrophobic change of the brush layer. Using TIRM, we have directly measured such an ion-pairing induced collapse transition of surface-confined polyelectrolyte brushes, even at very low specific anion concentrations.

This paper describes a simple and flexible method for fabricating polymeric particles with single-cavity structure by a modified soap-free emulsion polymerization (SFEP). The key is to introduce a functional comonomer (methyl methacrylate, MMA) and a crosslinker (divinylbenzene, DVB) to a conventional three-component SFEP system, followed by polymerization. Anisotropic latex particles with good monodispersity in both size and shape are directly produced in one-pot synthesis with a high yield. The importance of the presence of MMA and DVB in the SFEP with regards to the anisotropic particles formation is discussed.

Bimodal colloidal mixtures of nanoparticles and microparticles may show different phase behaviors depending upon the interparticle interaction of both species. In the present work, we examined the stabilization of spherical microparticles using highly charged, spherical nanoparticles. Total internal reflection microscopy (TIRM) was used to measure the interaction forces between a charged microparticle and flat glass substrate in aqueous solutions at varying volume fractions of nanoparticles of the same sign. We found that, in the system containing of highly charged nanoparticles, microparticle, and glass substrate, non-adsorbing charged nanoparticles in solution did not lead to depletion attraction. Instead, the addition of nanoparticles was to consistently create a repulsive force between the microparticle and glass substrate even at a very low nanoparticle volume fraction. This result might attributed to the formation of thin shells (halos) with a high local nanoparticle volume fraction to the region near the glass surface, resulting in electrostatic repulsion between the decorated surfaces. This study demonstrates that nanoparticle halos can also arise in binary systems of mutually but highly repulsive microparticle/nanoparticle dispersions.

We describe a flexible method for large-scale production of polymeric microspheres by templating a microgel-stabilized oil-in-water (o/w) high internal phase emulsion.

In a mixture of colloidal particles and polymer molecules, the particles may experience an attractive “depletion force” if the size of the polymer molecule is larger than the interparticle separation. This is because individual polymer molecules experience less conformational entropy if they stay between the particles than they escape the inter-particle space, which results in an osmotic pressure imbalance inside and outside the gap and leads to interparticle attraction. This depletion force has been the subject of several studies since the 1980s, but the direct measurement of this force is still experimentally challenging as it requires the detection of energy variations of the order of kBT and beyond. We present here our results for applying total internal reflection microscopy (TIRM) to directly measure the interaction between a free-moving particle and a flat surface in solutions consisting of small water-soluble organic molecules or polymeric surfactants. Our results indicate that stable nanobubbles (ca. 150 nm) exist free in the above aqueous solutions. More importantly, the existence of such nanobubbles induces an attraction between the spherical particle and flat surface. Using TIRM, we are able to directly measure such weak interaction with a range up to 100 nm. Furthermore, we demonstrate that by employing thermo-sensitive microgel particles as a depleting agent, we are able to quantitatively measure and reversibly control kBT-scale depletion attraction as function of solution pH.

Colloidosomes with porous shells have attracted attention in recent years because of the great potential as vehicles for controlled delivery of active ingredients. We present herein a simple and flexible method to prepare colloidosomes by a combination of particle-stabilized emulsion and solvent extraction method. We first generate an oil-in-water (o/w) emulsion where the dispersed phase is slightly soluble in the continuous phase and contains a water-insoluble polymer. Polystyrene particles, suspended in the dispersed phase, absorb onto the surface of oil droplet to stabilize the emulsions. The particles at the interface eventually become the shell of colloidosome microcapsules upon the removal of the oil by solvent-mediated diffusion. In addition, during the oil removal, the dissolved water-insoluble polymer likely deposits at the interface and binds the assembled polystyrene particles together, in turn leading to mechanical stable colloidosomes. We demonstrate that the size and morphology of the resultant colloidosome microcapsules depend on the type of the solvent and the oil extraction rate.Graphical abstractHighlights► Colloidosome microcapsules comprising particles and polymers as the shell can be prepared by combining the Pickering emulsion template and solvent-mediated diffusion method. ► A general method to generate colloidosome microcapsules in a high yield at room temperature without the need of centrifugation or washing. ► The size and morphology of the resultant colloidosome microcapsules can be controlled by the rate of the oil extraction.

Using pH- and thermo-responsive poly(N-isopropylacrylamide-co-methacrylic acid) (PNIPAM-co-MAA) microgels as an solely emulsifier, we have prepared a series of oil-in-water (o/w) highly concentrated emulsions with an internal phase ranging from 65% up to 80%. The resultant emulsions are gel-like and exhibit elastic properties due to the formation of a viscoelastic three-dimensional network of interconnected microgels and emulsion droplets. The dynamical rheology measurements show that elastic modulus (G′) of the emulsion increases as the internal phase volume increases. For a fixed internal phase volume, microgels are shown to stabilize emulsion with a high elasticity at room temperature above a solution pH of 6, but below this threshold, G′ decreases gradually with pH. This indicates that a stronger transient gel network is formed between the interconnected microgels and emulsions droplets at the high pH solutions. On the other hand, for emulsions prepared at pH 4.2, gel-to-fluid transition occurs when the temperature is raised to 37 °C, whereas the emulsions produced above pH 6 are stable even when heat at 60 °C for 12 h. Therefore, the formulated gel emulsion stabilized by the microgels shows their twofold responsiveness to pH and temperature.

Three-dimensionally interconnected, highly porous silica materials with ordering on three different scales, that is, macropores (10–30 μm), interconnecting windows (3–5 μm), and nanoporous walls (∼80 nm), are prepared via a dual-templating approach.

In the past, many laser light-scattering experimental results revealed that besides the fast relaxation mode, there existed an additional slow mode in semidilute solutions. This slow mode has been assigned to a variety of origins, but there has been no clear and well-accepted explanation. As the polymer concentration increases, the slow relaxation mode persists in the concentrated region, in melts and in gels in which polymer chains are crosslinked instead of entangled. The slow relaxation mode has also been reported for charged macromolecules in aqueous and nonaqueous solutions. However, it is generally thought to be different in nature from that observed in semidilute neutral polymer solution. In recent years, armed with novel solution preparation methods and some specially designed polymers, we have reexamined the dynamics of polymer chains, especially the slow mode, in semidilute neutral polymer solutions, dilute polyelectrolyte solutions and gels, which are reviewed here. Our results suggest that the slow mode can be qualitatively considered as hindered motions of interacting chains even though the nature of interaction can be very different; namely, from the weak segment–segment interaction in a less good solvent to strong electrostatic interaction among polyelectrolyte chains, and even to chemical crosslinking inside gel networks.

Total internal reflection microscopy was used to directly measure the interaction potentials between a micron-sized silica sphere and a flat silica surface in the presence of a linear poly(N-isopropylacrylamide) (PNIPAM) aqueous solution. When the PNIPAM concentration was low, no discernible forces were detected. A further increase in PNIPAM concentration resulted in a long-range attraction which was likely due to a combined of the reduced electrostatic interaction between the silica particle and the flat surface after the polymer adsorption and polymer bridges formation. On the other hand, for a fixed PNIPAM concentration, the interaction potential profiles between the particle and flat surface were once again characterized by attraction as temperature was increased. This attractive force can be explained in terms of the conformational changes of PNIPAM chains at the surfaces, which subsequently affected the polymer adsorption and enhanced the segment–segment interaction among the adsorbed polymer chains.

Polydimethylsiloxane-graft-poly(ethylene oxide) (PDMS-g-PEO) copolymers form micelles in water with PDMS as the core and PEO as the corona. The introduction of poly(acrylic acid)-block-polyacrylonitrile (PAA-b-PAN) block copolymers in water leads to the formation of micellar complexes due to the hydrogen bonding between carboxyl groups and ether oxygens among the PAA and PEO chains in the corona of the micelles. The effects of pH, molar ratios (r) of PAA/PEO, and the standing time on the directly mixing these two micelles in water have been investigated using laser light scattering (LLS) and transmission electron microscopy (TEM). Our results showed that the complexation between PAA and PEO in the corona was greatly enhanced at a pH below 3.5. For a fixed pH value, the interactions between these two micelles in water were governed by the value of r. At r < ∼0.6, mixing the two micelles in water resulted in a large floccule because the smaller PAA-b-PAN micelles act as physical cross-links, which are absorbed onto one PDMS-g-PEO micelle and simultaneously bonded to PEO chains on the other micelles, forming bridges and causing flocculation. At ∼0.6 < r < ∼1.2, the mixing led to stable micellar complexes with a layer of PAA-b-PAN micelles absorbed onto the initial PDMS-g-PEO micelles. At r > ∼1.2, the resultant micellar complexes first remained stable, but they precipitated from solution after a long time standing.

The fabrication of hollow microspheres to encapsulate functional molecules, such as drugs, insecticides, and proteins, is of ever-increasing importance. Many chemical and physicochemical methods have been tested for various specific encapsulations, but most of them have not been developed into an industrial process. In this work, we present a straightforward method to prepare liquid core−polymer shell microcapsules by first templating an oil-in-water emulsion stabilized by an interfacial monolayer of polystyrene latex particles (often referred to as “Pickering emulsion”), and subsequently locking the assembled particles into a robust polymeric shell through the precipitation of a biodegradable polymer poly(lactic-co-glycolic acid) (PLGA) at the interface. The resultant microcapsules that have a solid polymeric enveloped around the oil droplets are stable and retain their integrity during the drying in air. Therefore, they should have great potential to serve as vehicles for encapsulating functional molecules especially hydrophobic in nature.

Non-covalent intermolecular forces, such as van der Waals, electrostatic, steric, and hydrophobic interactions, have played essential roles in determining the association, aggregation, adhesion and sedimentation processes of colloidal particles, surfactant micelles, and macromolecules, in solutions and biological systems. These interaction forces, however, are normally weak (