Thermoresponsive polymer gels exhibit pronounced swelling and deswelling upon changes in temperature, accompanied by dynamic concentration fluctuations that have been interpreted as critical opalescence. These fluctuations span lengthscales similar to that of static structures in the gels, such as the gel polymer-network meshsize (1–10 nm) and static polymer-network crosslinking inhomogeneities (10–1000 nm). To systematically investigate this overlay, we use droplet-based microfluidics and fabricate submillimeter-sized gel particles with varying static heterogeneity, as revealed on a molecular scale by proton NMR. When these microgels are probed by small-angle neutron scattering, the detection of dynamic fluctuations during the volume phase transitions is strongly perturbed by the co-existing static inhomogeneity. Depending of the type of data analysis employed, the temperature-dependent evolution of the correlation length associated to the dynamic fluctuations does or does not agree with predictions by the critical scaling theory. Only the most homogeneous sample of this study, prepared by controlled polymer crosslinking in droplet microfluidics, shows a diverging correlation length in agreement to the critical scaling theory independent of the specific approach of data analysis. These findings suggest that care must be taken about polymer-network heterogeneity when gel volume phase transitions are evaluated as critical phenomena. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1112–1122

Polymer microgels consist of swollen networks of crosslinked macromolecules with particulate dimensions. If these networks exhibit a delicate interplay with their environment that allows them to be swollen and deswollen or to be crosslinked and decrosslinked upon external stimulation, they can serve for a variety of applications in sensing and actuation. Such environmental sensitivity can be realized either by the use of covalently crosslinked polymer networks that exhibit critical miscibility with their swelling medium or by the use of transient and reversible, supramolecular chain crosslinking. This article highlights some achievements in the synthesis and application of sensitive microgels. In one area of focus, the article discusses the use of sensitive microgels as model colloids to study relations between structure, dynamics, and properties of soft matter. In another area of focus, the paper discusses the use of these microgels to encapsulate, host, and release functional additives. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 435–449

Microgel capsules are micrometer-sized particles that consist of a cross-linked and swollen polymer network complexed with additives. These capsules can be actuated by external stimulation if they are formed from sensitive or supramolecular polymer networks. To make this truly useful, it is crucial to control the microgel size, shape, and loading; this can be achieved by droplet-based microfluidic templating.

Microgel capsules are micrometer-sized particles that consist of a cross-linked, solvent-swollen polymer network complexed with additives. These particles have various applications, such as drug delivery, catalysis, and analytics. To optimize the performance of microgel capsules, it is crucial to control their size, shape, and content of encapsulated additives with high precision. There are two classes of microgel-capsule structures. One class comprises bulk microcapsules that consist of a polymer network spanning the entire particle and entrapping the additive within its meshes. The other class comprises core–shell structures; in this case, the microgel polymer network just forms the shell of the particles, whereas their interior is hollow and hosts the encapsulated payload. Both types of structures can be produced with exquisite control by droplet-based microfluidic templating followed by subsequent droplet gelation. This article highlights some early and recent achievements in the use of this technique to tailor soft microgel capsules; it also discusses applications of these particles. A special focus is on the encapsulation of living cells, which are very sensitive and complex but also very useful additives for immobilization within microgel particles.

Thermoresponsive polymer gels exhibit pronounced swelling and deswelling upon changes in temperature, rendering them attractive for various applications. This transition has been studied extensively, but only little is known about how it is affected by nano- and micrometer-scale inhomogeneities in the polymer gel network. In this work, droplet microfluidics is used to fabricate microgel particles of strongly varying inner homogeneity to study their volume phase behavior. These particles exhibit very similar equilibrium swelling and deswelling independent of their inner inhomogeneity, but the kinetics of their volume phase transition is markedly different: while gels with pronounced micrometer-scale inhomogeneity show fast and affine deswelling, homogeneous gels shrink slowly and in multiple steps.

Microgel particles can be fabricated with great control by droplet-based microfluidics; however, to this end, their shape is intrinsically limited to be spherical. Existing approaches to circumvent this limitation rely on the rapid interception of transient non-spherical preparticle shapes, greatly limiting their versatility. This paper presents a facile microfluidic approach that overcomes this limitation. The method utilizes the injection of scaffolding microgel particles into droplets that have insufficient volumes to host the microgels in a spherical shell. As a result, the drops adopt non-spherical equilibrium shapes that serve to template non-spherical soft supraparticles by slow and gentle chemical reactions.