Microgels For Applications Research Articles

Rheology Applied to Microgels: Brief (Revision of the) State of the Art.

The ability of polymer microgels to rapidly respond to external stimuli is of great interest in sensors, lubricants, and biomedical applications, among others. In most of their uses, microgels are subjected to shear, deformation, and compression forces or a combination of them, leading to variations in their rheological properties. This review article mainly refers to the rheology of microgels, from the hard sphere versus soft particles’ model. It clearly describes the scaling theories and fractal structure formation, in particular, the Shih et al. and Wu and Morbidelli models as a tool to determine the interactions among microgel particles and, thus, the viscoelastic properties. Additionally, the most recent advances on the characterization of microgels’ single-particle interactions are also described. The review starts with the definition of microgels, and a brief introduction addresses the preparation and applications of microgels and hybrid microgels.

Aqueous microgels with engineered hydrophobic nano-domains

We evaluate recent developments in the design, synthesis, and application of microgels with an amphiphilic polymer network with regard to the structure of their hydrophobic domains.

Poly(N-isopropylacrylamide) microgels at the oil–water interface: adsorption kinetics

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.

A new approach towards “active” self-healing coatings: exploitation of microgels

Micron sized gel particles (microgel) are a new type of material that can be used as an “active” part of a self-healing coating system. Application of microgels is very advantageous, since they combine the attractive properties of both solids and liquids. The solid state of the particles, provided by a cross-linked polymer network, ensures good mechanical stability of the resulting coating system. The liquid corrosion inhibitor, being entrapped in the solid matrix, retains its mobility, providing the coating system with self-healing capabilities. The synthesis route of the microgel is comparatively easy and can be realized via a one-pot process, which makes the whole approach very promising for application in “real” systems. Superior corrosion protection of the resulting self-healing system containing synthesized microgel particles as an “active” part in comparison to the original coating was demonstrated by means of the scanning vibrating electrode technique and electrochemical impedance spectroscopy.

Functionalised Microgels for Acrylic Coatings

AbstractSummary: Aqueous acrylic dispersions of hydroxy‐functionalised copolymer microgel particles crosslinked with allyl methacrylate were synthesized by emulsion polymerization. The microgels were investigated as reactive polymer fillers in mixtures with a water‐borne film‐forming dispersion. Properties of coatings cast from mixtures of aqueous dispersion of hard microgel particles and film‐forming water‐borne dispersion were investigated. The swelling behaviour of microgels in selected solvents (aliphatic ketones) as a function of microgel composition is discussed as well. It was found that the swelling ability of microgels decreased with growing degree of crosslinking. Microgels comprising copolymerised butyl methacrylate swelled less in aliphatic ketones than microgels without this comonomer. This work was focused mainly on the influence of microgels incorporated in the commercial solvent‐borne acrylic binders on the properties of coatings. It was shown that the application of microgels that were redispersed in acetone did not affect the surface appearance and transparency of coatings. Moreover, the presence of microgel network precursors accelerated film curing at ambient temperature and improved the final hardness of coatings.

Application of microgels as polymer supports for organic synthesis: preparation of a small phthalide library, a scavenger, and a borohydride reagent.

Microgel polymers containing a series of functional groups have been prepared. These microgels were composed of cross-linked poly(styrene) and were prepared by radical polymerization in solution. The microgel polymers exhibit good solubility in an array of different organic solvents, and in addition, they can be efficiently precipitated by the addition of methanol and isolated by filtration. A nine-member phthalide library was synthesized using an aminomethyl-functionalized microgel 5. To further demonstrate the versatility of these microgel polymers, tris(2-aminoethyl)amino microgel 11 was examined as a scavenger reagent to remove unreacted isocyanate after a urea synthesis. Finally, a microgel-supported ammonium borohydride reagent 14 was successfully prepared and used as a reducing agent. Notable features of these microgels are that in all applications the progress of the reaction could be monitored by standard NMR techniques and their preparation is performed using common glassware and techniques found in all organic laboratories.

Preparation of microgels and their industrial application as fluidity controlling agents

AbstractMicrogels, intramolecularly crosslinked macromolecules with sizes of less than 100 nm, were originally manufactured via an emulsion polymerization process involving the use of novel amphiphilic oligomers containing the zwitterion moiety as emulsifiers. Application of microgels as additives to coatings has been studied here. Newtonian flow of an original coating composition was altered to pseudoplastic flow by the addition of microgels. The mechanism of this fluidity alteration was discussed in terms of electron microscopic observation of the coating composition.