Seeded Emulsion Polymerization of Styrene in the Presence of Water-Swollen Hydrogel Microspheres

Clarification of Surface Deswelling of Thermoresponsive Microgels by Electrophoresis

Although many investigations of thermoresponsive microgels have been reported, their surface properties, which are crucial in colloid science, are still not fully understood. In this study, microgels with surface-localized charged groups were synthesized by precipitation polymerization, and their electrophoretic behaviors were analyzed using a modified version of Ohshima's equation to obtain two surface properties of the soft particles: the softness parameter and the surface charge density. This systematic evaluation allows us to discuss the thermoresponsiveness of the overall microgels and their surfaces separately. Furthermore, the validity of the surface properties obtained from electrophoresis was verified by comparing them with the results of seeded emulsion polymerization in the presence of the microgels and the force-indentation curves obtained via high-speed atomic force microscopy (HS-AFM).

Durable gelfoams stabilized by compressible nanocomposite microgels

Compressible nanocomposite microgels can stabilize the air/water interfaces of gas bubbles for several months, which affords durable gelfoams.

Importance of pH in Synthesis of pH-Responsive Cationic Nano- and Microgels

While cationic microgels are potentially useful for the transfection or transformation of cells, their synthesis has certain drawbacks regarding size, polydispersity, yield, and incorporation of the cationic comonomers. In this work, a range of poly(N-isopropylacrylamide) (PNIPAM) microgels with different amounts of the primary amine N-(3-aminopropyl)methacrylamide hydrochloride (APMH) as the cationic comonomer were synthesized. Moreover, the pH-value during reaction was varied for the synthesis of microgels with 10 mol% APMH-feed. The microgels were analyzed by means of their size, thermoresponsive swelling behavior, synthesis yield, polydispersity and APMH-incorporation. The copolymerization of APMH leads to a strong decrease in size and yield of the microgels, while less than one third of the nominal APMH monomer feed is incorporated into the microgels. With an increase of the reaction pH up to 9.5, the negative effects of APMH copolymerization were significantly reduced. Above this pH, synthesis was not feasible due to aggregation. The results show that the reaction pH has a strong influence on the synthesis of pH-responsive cationic microgels and therefore it can be used to tailor the microgel properties.

Hydrophobic Monomers Recognize Microenvironments in Hydrogel Microspheres during Free-Radical-Seeded Emulsion Polymerization

The three-dimensional structure of nanocomposite microgels was precisely determined by cryo-electron micrography. Several nanocomposite microgels that differ with respect to their nanocomposite structure, which were obtained from seeded emulsion polymerization in the presence of microgels, were used as model nanocomposite materials for cryo-electron micrography. The obtained three-dimensional segmentation images of these nanocomposite microgels provide important insights into the interactions between the hydrophobic monomers and the microgels, that is, hydrophobic styrene monomers recognize molecular-scale differences in polarity within the microgels during the emulsion polymerization. This result led to the formation of unprecedented multi-layered nanocomposite microgels, which promise substantial potential in colloidal applications.

Recent advances in stimuli-responsive core-shell microgel particles: synthesis, characterisation, and applications

Inspired by the path followed by Matthias Ballauff over the past 20 years, the development of thermosensitive core-shell microgel structures is reviewed. Different chemical structures, from hard nanoparticle cores to double stimuli-responsive microgels have been devised and successfully implemented by many different groups. Some of the rich variety of these systems is presented, as well as some recent progress in structural analysis of such microstructures by small-angle scattering of neutrons or X-rays, including modelling approaches. In the last part, again following early work by the group of Matthias Ballauff, applications with particular emphasis on incorporation of catalytic nanoparticles inside core-shell structures—stabilising the nanoparticles and granting external control over activity—will be discussed, as well as core-shell microgels at interfaces.

Hydrophobized nanocomposite hydrogel microspheres as particulate stabilizers for water-in-oil emulsions

Hydrophobized nanocomposite microgels can serve as particulate emulsifiers for water-in-oil (W/O) emulsions with different types of oils, including non-polar oils, which usually do not form W/O emulsions with conventional microgels.