Particles Trapped at the Droplet Interface in Water-in-Water Emulsions

Water-in-water emulsions were formed by mixing incompatible aqueous solutions of dextran and poly­(ethylene oxide) (PEO) in the presence of latex or protein particles. It was found that particles with a radius as small as 0.1 μm become trapped at the interface between the PEO- and dextran-rich phases with interfacial tensions down to 10^–6 N/m. The particles were visualized at the interface of the emulsion droplets using confocal laser scanning microscopy (CLSM) allowing determination of the contact angle. Various degrees of coverage with particles could be observed. On densely covered droplets, the particles had a hexagonal crystalline order. At intermediate coverage, transient clustering of the particles was observed. The diffusion coefficient of the particles at the interface was determined using multiparticle tracking. Fusion of droplets was observed in all cases leading eventually to macroscopic phase separation

Dynamic Mechanical Properties of Networks of Wormlike Micelles Formed by Self-Assembled Comblike Amphiphilic Copolyelectrolytes

The rheological properties of viscoelastic aqueous solutions of wormlike micelles formed by the self-assembly of comblike copolyelectrolytes have been investigated by flow and dynamic measurements. The comblike polymers consisted of a polystyrene backbone grafted with a fixed amount of pendant <i>N</i>,<i>N</i>-dimethyl quaternary ammonium alkyl groups of various lengths ranging from C12 up to C18. Upon increasing concentration, the increase in size of the wormlike micelles and their branching results in the formation of a system spanning network through a percolation process at a critical concentration that decreases when salt is added or when the temperature is decreased. In this manner transient gels are formed with a viscoelastic relaxation time that does not depend on the polymer concentration or on the ionic strength, but their elastic modulus increases with increasing polymer or salt concentration. When the size of the alkyl groups is increased from C12 to C16, the relaxation time increases very strongly, but the temperature dependence remains characterized by the same activation energy. For C18, the systems are frozen at least up to 80 °C

Particles Trapped at the Droplet Interface in Water-in-Water Emulsions

Water-in-water emulsions were formed by mixing incompatible aqueous solutions of dextran and poly­(ethylene oxide) (PEO) in the presence of latex or protein particles. It was found that particles with a radius as small as 0.1 μm become trapped at the interface between the PEO- and dextran-rich phases with interfacial tensions down to 10^–6 N/m. The particles were visualized at the interface of the emulsion droplets using confocal laser scanning microscopy (CLSM) allowing determination of the contact angle. Various degrees of coverage with particles could be observed. On densely covered droplets, the particles had a hexagonal crystalline order. At intermediate coverage, transient clustering of the particles was observed. The diffusion coefficient of the particles at the interface was determined using multiparticle tracking. Fusion of droplets was observed in all cases leading eventually to macroscopic phase separation

Particles Trapped at the Droplet Interface in Water-in-Water Emulsions

Water-in-water emulsions were formed by mixing incompatible aqueous solutions of dextran and poly­(ethylene oxide) (PEO) in the presence of latex or protein particles. It was found that particles with a radius as small as 0.1 μm become trapped at the interface between the PEO- and dextran-rich phases with interfacial tensions down to 10^–6 N/m. The particles were visualized at the interface of the emulsion droplets using confocal laser scanning microscopy (CLSM) allowing determination of the contact angle. Various degrees of coverage with particles could be observed. On densely covered droplets, the particles had a hexagonal crystalline order. At intermediate coverage, transient clustering of the particles was observed. The diffusion coefficient of the particles at the interface was determined using multiparticle tracking. Fusion of droplets was observed in all cases leading eventually to macroscopic phase separation

Particles Trapped at the Droplet Interface in Water-in-Water Emulsions

Water-in-water emulsions were formed by mixing incompatible aqueous solutions of dextran and poly­(ethylene oxide) (PEO) in the presence of latex or protein particles. It was found that particles with a radius as small as 0.1 μm become trapped at the interface between the PEO- and dextran-rich phases with interfacial tensions down to 10^–6 N/m. The particles were visualized at the interface of the emulsion droplets using confocal laser scanning microscopy (CLSM) allowing determination of the contact angle. Various degrees of coverage with particles could be observed. On densely covered droplets, the particles had a hexagonal crystalline order. At intermediate coverage, transient clustering of the particles was observed. The diffusion coefficient of the particles at the interface was determined using multiparticle tracking. Fusion of droplets was observed in all cases leading eventually to macroscopic phase separation

Effect of Arm Exchange on the Liquid–Solid Transition of Dense Suspensions of Star Polymers

Star polymers with dynamic arm exchange are formed in water by self-assembly of amphiphilic diblock copolymers based on poly­(ethylene oxide) end capped with a small hydrophobic block. The arm exchange was arrested <i>in situ</i> by photo-cross-linking of the core. The effect of dynamic arm exchange on the osmotic compressibility and viscosity was investigated systematically as a function of the concentration and temperature. The discontinuous liquid–solid transition reported for dense polymeric micelle suspensions was found to be preserved after dynamic arm exchange was arrested <i>in situ</i>. The effect of cross-linking and aggregation number on the liquid–solid transition was investigated

Stabilization of Water-in-Water Emulsions by Polysaccharide-Coated Protein Particles

The phase diagram of mixtures of xyloglucan (XG) and amylopectin (AMP) in aqueous solution is presented. Water-in-water emulsions prepared from mixtures in the two-phase regime were studied in detail, and the interfacial tension was determined. It is shown that the emulsions can be stabilized by addition of β-lactoglobulin microgels (βLGm), but only at pH ≤ 5.0. Excess βLGm preferentially entered the AMP phase at pH > 5.0 and the XG phase at lower pH. The inversion was caused by adsorption of XG onto βLGm that started below pH 5.5. It is shown that modification of the surface of particles by coating with polysaccharides is a potential lever to control stabilization of water-in-water emulsions

pH-Responsive Water-in-Water Pickering Emulsions

The structure and stability of water-in-water emulsions was investigated in the presence of spherical, pH-sensitive microgels. The emulsions were formed by mixing aqueous solutions of dextran and PEO. The microgels consisted of cross-linked, synthetic polymers with a radius that steeply increased from 60 to 220 nm with increasing pH within a narrow range around 7.0. At all pH values between 5.0 and 7.5, the microgels were preferentially situated at the interface, but only in a narrow range between pH 7.0 and 7.5, the emulsions were stable for at least 1 week. The droplet size was visualized with confocal laser scanning microscopy and was found to be smallest in the stable pH range. Emulsions could be stabilized or destabilized by small changes of the pH. Addition of small amounts of salt led to a shift of the pH range where the emulsions were stable. The effects of varying the microgel concentration and the polymer composition were investigated