Small but Smart:
Sensitive and Supramolecular Microgel Capsules and Model Colloids
Freie Universität Berlin, Institute of Chemistry and Biochemistry, Berlin, Germany email@example.com
"Smart" microgels are micrometer-sized polymer gel particles that react to external stimuli, either by selective swelling and deswelling or by triggered crosslinking and decrosslinking. The first class of response is achieved through the use of microgels that are composed of polymers with sensitive solubility,1 whereas the second class of response is realized by reversible supramolecular polymer crosslinking rather than permanent chemical crosslinking.2 Both classes of response are attractive for practical applications; they are also useful in fundamental research, where microgels serve to build and investigate complex soft matter.3 A powerful approach to fabricate smart microgels with exquisite control is through the use of droplet-based microfluidic templating.1 The idea of this approach is to use emulsion droplets as templates for the particle synthesis and to control the size, shape, and monodispersity of the microgels by controlling the size, shape, and monodispersity of the pre-microgel droplets. To extend this control towards controlling the microgel material properties, this approach can be combined with the use of functional, macromolecular precursors, allowing the polymer synthesis and the particle gelation to be controlled independently.4 This approach also allows complex particle morphologies such as hollow,4 anisotropic,5 or multi-layered6,7 microgels to be formed and complexed with additives, including living cells.8 Such particles are particularly useful in encapsulation and controlled release applications.6,9 In addition to their utility for encapsulation, responsive microgels can serve as model colloids to study the mechanics and dynamics of soft matter. For example, this approach allows exploring how nanostructural inhomogeneities affect the behavior of sensitive polymer gels. To study this effect, droplet-based microfluidics can be used to fabricate micrometer-sized gel particles that are complexed with a precisely controlled degree of internal inhomogeneities, offering the possibility to study their impact.10 A particularly powerful strategy is to combine droplet-based microfludics and small-angle x-ray scattering.11 In addition, microgels can be used as building blocks to create larger soft materials, providing another means of purposely creating inhomogeneous composite systems to be studied.12 With these approaches, fundamental understanding of the effect and evolution of nanostructural complexity in sensitive gels can be achieved and employed in rational design of advanced soft materials.13
1) Seiffert, S. Macromol. Rapid Commun. 2011, 32, 1600
2) Seiffert, S.; Sprakel, J. Chem. Soc. Rev. 2012, 41, 309
3) Menut, P.; Seiffert, S.; Sprakel, J.; Weitz, D. A. Soft Matter 2012, 8, 156
4) Seiffert, S.; Weitz, D. A. Soft Matter 2010, 6, 3184
5) Seiffert, S.; Romanowsky, M. B.; Weitz, D. A. Langmuir 2010, 26, 14842
6) Seiffert, S.; Thiele, J.; Abate, A. R.; Weitz, D. A. J. Am. Chem. Soc. 2010, 132, 6606
7) Seiffert, S. Macromol. Rapid. Commun. 2012, 33, 1286
8) Rossow, T.; Heyman, J. A.; Ehrlicher, A. J.; Langhoff, A.; Weitz, D. A.; Haag, R.; Seiffert, S. J. Am. Chem. Soc. 2012, 134, 4983
9) Seiffert, S. ChemPhysChem 2013, 14, 295.
10) Seiffert, S. Macromol. Rapid Commun. 2012, 33, 1135
11) Stehle, R.; Goerigk, G.; Wallacher, D.; Ballauff, M.; Seiffert, S. Lab Chip 2013, 13, 1529.
12) Di Lorenzo, F.; Seiffert, S. Macromolecules 2013, 46, 1962.
13) Rossow, T.; Hackelbusch, S.; Van Assenbergh, P.; Seiffert, S. Polymer Chem. 2013, 4, 2515.