Schaltbare Mikrogele an Öl-Wasser Grenzflächen
Final Report Abstract
This project has successfully shed light on the understanding peculiar properties of microgels at oil-water interfaces. Microgels are strongly swollen, lyophilic particles that lower the interfacial tension of oil-water interfaces and stabilize emulsion droplets. Temperature and pH-sensitive microgels allow preparing temperature and pH-sensitive emulsions and thus enables to prepare and break emulsions on demand. Although such emulsions are sensitive to pH, the stabilization of droplets is not due to electrostatic repulsion, instead the viscoelastic properties of the interface seem to dominate droplet stability. Being soft and porous, microgels behave distinctly different from rigid particles at the interface: they are deformed and strongly flattened especially in the case of oil-in-water emulsions. The microgels are located mainly in the aqueous side of the interface for both oilin-water and water-in-oil emulsions. In contrast to rigid, solid particles, the behavior of microgels at oil-water interfaces does not depend only on the interfacial tension, but the balance between interfacial tension, swelling, elasticity and deformability of the microgel needs to be considered. The softer and more swollen the microgels are, the better they stabilize emulsions. It is obvious that microgels as soft and porous particles are significantly different from classical rigid colloidal stabilizers in Pickering emulsions. They open the door for new, sophisticated applications as, e.g. in bio-technology.
Publications
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Emulsions Stabilized by Stimuli-Sensitive Poly(N-Isopropylacrylamide)-Co-Methacrylic Acid Polymers: Microgels Versus Low Molecular Weight Polymers. Langmuir 2008, 24, 7769–7777
Brugger, B.; Richtering, W.
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Microgels as Stimuli-Responsive Stabilizers for Emulsions. Langmuir 2008, 24, 12202–12208
Brugger, B.; Rosen, B. A.; Richtering, W.
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The Colloidal Suprastructure of Smart Microgels at Oil–Water Interfaces. Angew. Chem. Int. Ed. 2009, 48, 3978–3981
Brugger, B.; Rütten, S.; Phan, K.-H.; Möller, M.; Richtering, W.
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Interfacial Layers of Stimuli-Responsive Poly-(N-Isopropylacrylamide-Co-Methacrylicacid) (PNIPAM-Co-MAA) Microgels Characterized by Interfacial Rheology and Compression Isotherms. Phys Chem Chem Phys 2010, 12, 14573–14578
Brugger, B.; Vermant, J.; Richtering, W.
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Influence of Microgel Architecture and Oil Polarity on Stabilization of Emulsions by Stimuli-Sensitive Core–Shell Poly(N-Isopropylacrylamide-Co-Methacrylic Acid) Microgels: Mickering Versus Pickering Behavior? Langmuir 2011, 27, 9801–9806
Schmidt, S.; Liu, T.; Rütten, S.; Phan, K.-H.; Möller, M.; Richtering, W.
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Non-Coalescence of Oppositely Charged Droplets in pH-Sensitive Emulsions. Proc. Natl. Acad. Sci. U.S.A. 2012, 109, 384–389
Liu, T.; Seiffert, S.; Thiele, J.; Abate, A. R.; Weitz, D. A.; Richtering, W.
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Responsive Emulsions Stabilized by Stimuli-Sensitive Microgels: Emulsions with Special Non-Pickering Properties. Langmuir 2012, 28, 17218–17229
Richtering, W.
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Unraveling the 3D Localization and Deformation of Responsive Microgels at Oil/Water Interfaces: a Step Forward in Understanding Soft Emulsion Stabilizers. Langmuir 2012, 28, 15770–15776
Geisel, K.; Isa, L.; Richtering, W.
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Microgel-Stabilized Smart Emulsions for Biocatalysis. Angew. Chem. Int. Ed. 2013, 52, 576–579
Wiese, S.; Spiess, A. C.; Richtering, W.
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Poly(N-Isopropylacrylamide) Microgels at the Oil–Water Interface: Adsorption Kinetics. Soft Matter 2013, 9, 9939–9946
Li, Z.; Geisel, K.; Richtering, W.; Ngai, T.
