Nanogel/Microgel Science and Beyond

Abstract

Since the first report in 1986, tremendous effort has been devoted to developing a deeper understanding of hydrogel colloidal particles (i.e., nanogels/microgels), including their synthesis, characterization, assembly, computer simulation, and various applications. At present, many researchers from diverse scientific backgrounds are using nanogels/microgels for their own research purposes, and thus, there seem to be several miscommunications. Here, in order to further accelerate the development of the nanogel/microgel research field, a personal viewpoint on this research topic is presented.

The compression of deformed microgels at an air/water interface

“…We have already reported that the ordered structure of microgels adsorbed at the air/water interface of a sessile droplet differs from that on a substrate after drying (removal of water), which is mainly due to the decrease of interpenetration between neighboring microgels at the air/water interface. 13 c,d,f ,15 Thus, in this study, the lower crosslinked CS0.60 and CS0.66 microgels with thicker shell layers promote interpenetration with each other and prevent microgel arrays from disordering. Moreover, it was clarified that the disordering of microgel arrays is also related to the degree of compression when transferring them to solid substrates.…”

“…However, this transfer may lead to structural changes of microgel arrays since the structures of microgel arrays are not always the same at fluid interfaces as they are on solid substrates. 13 c ,14 d ,15 Therefore, one could argue that the compression of deformed microgels at fluid interfaces has not yet been fully understood.…”

Thermoresponsive Fluorescent Microgels through In Situ [2 + 2] Photocycloaddition Cross-Linking of Thermally Induced Aggregates of Dendrimers

“…Microgels are colloidal cross-linked polymer networks swollen by the solvents. Microgels display tunable structures, morphologies, viscoelasticity, and easy functionalization, which have shown broad applications in drug delivery, imaging, sensors, and bioseparation. − Microgels can be additionally made responsive to external stimuli to expand their functions, including temperature, pH, redox, light, and force. − Thermoresponsive microgels are particularly interesting as their sizes and physicochemical properties can be reversibly tuned through thermally induced volume phase transition. , Thermoresponsive microgels were conventionally synthesized by precipitation or dispersion polymerization of vinyl monomers such as N -isopropylacrylamide in the presence of chemical cross-linkers. ,,, These methods are simple and easily scaled up to produce uniform microgels but often need to use surfactants or additive stabilizers, which are hard to be removed completely. In addition, the sizes and internal structures of the microgels are strongly affected by polymerization kinetics. ,, …”

Dual-responsive colloidosome-like microgels as the building blocks for phase inversion of Pickering emulsions

“…Microgels are a class of polymer particles that have distinctive interfacial properties, including a combination of surfactant and solid particle characteristics when adsorbed at the oil–water interface. 5–9 Furthermore, the incorporation of numerous monomers through copolymerization enhances the ability of polymer-based microgels to exhibit exceptional sensitivity to diverse environmental stimuli. 10,11 This characteristic renders them highly suitable as soft particles for the preparation of Pickering emulsions that can respond to many stimuli.…”